ALAT PENGHEMAT PENGGUNAAN BBM

Artikel ini dalah pengalaman penulis sendiri yang sengaja disosialisasikan kepada pembaca, khususnya pembaca yang mempunyai hobi/senang mengutak-atik sendiri kedaraan bermotor (bensin) dengan tujuan untuk menekan biaya operasional penggunaan kendaraan bermotor, khususnya penggunaan BBM (bensin).

Pendahuluan.Karena kita ketahui bahwa dimanapun kita menggunakan kendaraan bermotor terutama dalam kota, kemacetan lalu lintas adalah menjadi masalah yang sukar dihindari dan mengakibatkan banyak kehilangan waktu serta biaya (untuk pembelian bensin) yang kesemuanya itu berdampak pada faktor psikis pemakai/pengguna kendaraan itu sendiri.
Aspek teknis
Berbekal hanya pengetahuan dasar tentang motor bakar ditambah dengan baca sana-sini artikel-artikel automotive, penulis mencoba mengadakan analisa praktis dalam upaya mendapatkan hasil/tenaga yang maksimun dari penggunaan bahan bakar yang paling ekonomis dari suatu motor bakar, khususnya mesin yang menggunakan carburator. Hal dimaksud adalah :
• Bahan Bakar. Kita ketahui bahwa bahan bakar (bensin) mempunyai grade yang ditentukan oleh Octan Number. Kualitas bahan bakar yang baik dimaksud disamping ditentukan oleh Octan Number tadi, juga ditentukan oleh kemurnian bahan bakar itu sendiri. Dalam arti jumlah atau prosentase bahan lain yang terkandung/tercampur dalam bahan bakar tersebut jumlahnya kecil. Akhir-akhir ini banyak penjual-penjual bensin yang mengoplos dengan bahan lain untuk meraup keuntungan yang lebih besar tanpa memperdulikan akibatnya kepada pemakai kendaraan.
• Api/pengapian. Agar supaya bahan bakar yang telah ada diruang bakar terbakar diperlukan api (pengapian). Sedangkan untuk menghasilkan api yang baik, maka sistem pe-ngapian haruslah :
 Voltage yang keluar dari coil harus mencapai 18.000-20.000 V/DC.
 Tidak ada kebocoran arus listrik.
 Titik-titik sambung harus bersih.
 Sekecil mungkin kehilangan tegangan/arus akibat tahanan peralatan sistem (kabel-kabel).
• Campuran bahan bakar dan udara. Bahan bakar sebelum masuk keruang bakar akan dicampur dengan udara oleh Carburator. Baik bahan bakar maupun udara bisa diatur sendiri oleh kita sehingga mendapatkan perbandingan yang tepat. Namun demikian perbandingan yang tepat dari bahan bakar dan udara tersebut belum dapat dikatakan mempunyai kwalitas jika campuran belum merata artinya campuran yang mengisi tiap titik/sudut pada ruang bakar harus sama dalam perbandingan yang tepat.
Aplikasinya.
Dari ketiga hal tersebut diatas, penulis ingin menguraikan 1 hal saja yang sangat berpengaruh dan langsung dapat terasa manfaatnya yaitu memperbaiki kualitas campuran bahan bakar dan udara. Dalam keadaan normal/standar campuran bahan bakar dan udara yang telah ada diruang bakar suatu motor bakar akan terbakar 60-70% saja, sedang sisanya yang masih potensial bisa terbakar dan menghasilkan tenaga terbuang begitu saja. Prosentase yang terbakar tersebut masih bisa dinaikkan lagi menjadi 70-90% dengan cara campuran bahan bakar dan udara sebelum masuk ruang bakar diputar (cyclone) terlebih dahulu sehingga campuran tersebut betul-betul merata. Memang pada dekade tahun 90-an ada produk alat pemutar udara yang masuk carburator.
Analisa penulis, alat pemutar udara tersebut akan efektif jika dipasang pada “in take”/dimulut masuk ruang bakar artinya bahan bakar dan udara di campur dahulu baru diputar, bukan udara diputar dahulu lalu dicampur bahan bakar seperti produk pabrik yang ada dipasaran. Namun demikian jika alat pemutar tersebut dipasang pada “in take” tiap ruang bakar, maka sungguh sangat repot dan memerlukan biaya yang cukup besar untuk peralatan dan pemasangannya, karena jumlahnya ba-nyak (sesuai jumlah cylinder) dan pemasangannya menjadi tidak praktis/harus membongkar monifold. Dengan tetap berpegang pada prinsip bahan bakar dan udara di campur dahulu baru diputar, penulis mencoba mengambil jalan te-ngah yaitu dengan memasang alat pemutar tersebut dibawah carburator. Hal terpenting dari pemasa-ngan alat pemutar ini adalah tidak mempunyai dampak lain, terutama kenaikan suhu mesin karena kita tidak memaksakan mesin untuk mengikuti kehendak kita, tapi sebaliknya kita mengikuti kehendak mesin. Berikut cara pembuatan dan pemasangan alat pemutar/pe-ngirit pemakaian bahan bakar dimaksud :
• Kita ambil packing carburator dimaksud, kalau tidak ada terpaksa kita membongkar dulu dudukan carburator dan mencetaknya dalam karton (seperti halnya membuat pac-king) untuk dipakai sebagai ukuran standard (untuk carburator yang 2 lobang dipasang kedua-duanya).


• Sesuai dengan ukuran dan bentuk packing tersebut lalu dibuat dari bahan seng yang agak tebal (±0,5 mm), namun diameter lubang carburatornya dibuat lebih kecil 2 kali ketebalan seng yang dipakai.

• Membuat bahan pemutar dari seng sebanyak 8 lembar dengan ukuran panjang = jari-jari lubang carburator dan lebar ±1,5 cm – 2 cm.

• Kedelapan lembar bahan pe-mutar di las pada lubang carburator tersebut.

• Masing-masing daun pemutar ditekuk 45° dengan tang (se-perti baling-baling)

• Buat penutup samping dari daun-daun pemutar sesuai diameter lubang carburator dan panjang sesuai daun pemutar.

• Di las menutupi daun-daun pemutar.

• Setelah benjolan-benjolan las dirapikan/dihaluskan lalu alat tersebut dipasang dibawah carburator dengan packing atas bawah alat pemutar (seperti memakai packing biasa).

Gambar 8 Carburator dengan paking atas bawah alat pemutar.
• Cara penyetelannya. Sebelum mesin dinyalakan/dijalankan, sebaiknya kita siapkan terlebih dahulu beberapa buah spuyer yang ukurannya lebih kecil dari spuyer yang telah terpasang dalam carburator. Syukur kalau kita tahu pasti ukuran spuyer yang terpasang tersebut, jadi kita tinggal menyiapkan spuyer-spuyer pengganti yang lebih kecil ukurannya 15-25%. Untuk mencegah adanya kebocoran pada pemasangan alat ini, kedua sisi (atas dan bawah) alat pemutar ini dipasang packing (lihat gambar 8).
Setelah alat pemutar ini terpasang dengan rapi, dan pada saat kita coba menjalankan mesin maka putaran mesin akan menjadi tinggi dari pada sebelum alat ini dipasang, walaupun dalam keadaan stationer (Idle RUN). Jalan satu-satunya untuk mengembalikan putaran mesin kepada/menjadi putaran sebelum alat terpasang yaitu dengan mengganti spuyer yang lebih kecil (sebelumnya telah kita siapkan).
Penutup. Apabila spuyer baru yang telah dipasang masih belum cocok (mesin berputar masih ter-lalu cepat atau terlalu lambat). Kita ganti lagi spuyer tersebut sehingga mesin dapat berputar dengan kecepatan relatif sama dengan saat alat pemutar ini belum dipasang. Yang jelas dalam hal ini adalah spuyer yang dipasang dengan mengikuti kei-nginan mesin. Setelah yakin bahwa spuyer yang cocok terpasang para pembaca tinggal mencoba menjalankan kendaraan anda, dan jangan lupa untuk selalu mengevaluasi dan menganalisanya selama memakai alat pemutar/pengirit bensin tadi. Demikian sekilas tulisan populer tentang Alat Penghemat Penggunaan BBM.

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MANFAAT KULIT PISANG

Pisang memiliki banyak manfaat, antara lain :
a.Sebagai sumber tenaga
Gula pisang merupakan gula buah, yaitu terdiri dari fruktosa yang mempunyai indek

glikemik (laju perubahan makanan diubah menjadi gula dalam tubuh) lebih rendah dibandingkan dengan glukosa, sehingga cukup baik sebagai penyimpan energi karena sedikit lebih lambat dicerna. Untuk melakukan aktivitasnya, otak memerlukan energi berupa glukosa.

Glukosa darah sangat vital bagi otak untuk dapat berfungsi dengan baik, antara lain diekspresikan dalam kemampuan daya ingat. Glukosa darah terutama didapat dari asupan makanan sumber karbohidrat. Pisang adalah alternatif terbaik untuk menyediakan energi di saat-saat istirahat atau jeda, pada waktu otak sangat membutuhkan energi yang cepat tersedia untuk aktivitas biologis

b.Obat diare
Potasium (K) dan magnesium yang terkandung di dalam pisang amat sesuai merawat orang yang mengalami mencret. Potasium adalah mineral penting dalam nutrisi tubuh manusia yang juga menyeimbangkan elektron dalam tubuh. Kekurangan potassium dapt menyebabkan diare. Sementara pisang dapat menggantikan potasium yang diperas saat diare

c. Mengatasi kolestrol
Pisang rendah dari segi kalori lemak dan sodium (Na), serta mengandung potasium yang membantu merendah kolestrol. Potasium bekerja dengan sodium untuk mengatur keseimbangan cairan, denyut jantung, kontraksi otot, dan rangsangan saraf. Ketika tingkat potasium meningkat, tingkat sodium akan turun. Ini artinya makan kaya potasium dapat membantu mengimbangi pengaruh konsumsi sodium berlebihan seperti retensi cairan dan tekanan darah tinggi

d. Penderita anemia
Anemia ialah penyakit kurang darah. Dua pisang yang dimakan oleh pasien anemia setiap hari sudah cukup, karena mengandung Fe (zat besi) tinggi. Kerena pisang kaya dengan zat besi, ia boleh merangsang penghasilan hemoglobin di dalam darah.

e. Manfaat bagi luka bakar
Daun pisang juga dapat unutk mengaobati luka bakar, yaitu dengan cara kulit dioles campuran abu daun pisang ditambah minyak kelapa mempunyai pengaruh mendinginkan kulit.

f. Mengatur berat badan
Pisang juga mempunyai peranan dalam penurunan berat badan dan menaikkan berat badan. Telah terbukti seseorang kehilangan berat badan dengan berdiet empat buah pisang dan empat gelas susu non fat atau susu cair per hari sedikitnya 3 hari dalam seminggu, jumlah kalori hanya 1250 dan menu tersebut cukup menyehatkan. Selain itu, diet tersebut membuat kulit wajah tidak berminyak dan bersih. Pada sisi lain, mengkonsumsi satu gelas banana milk-shake dicampur madu, buah-buahan, kacang, dan mangga sesudah makan dapat menaikkan berat badan. ( KI - Henry-A2 )

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ISTILAH YUNANI DAN LATIN DALAM KIMIA

Sebaiknya kita mengenal beberapa istilah Yunani ataupun Latin yang sringkali kita gunakan dalam bekajar ilmu kimia. Misalnya : mono- uni- satu, di- bi- dua, tri- ter- tiga

tetra- quadri- empat
penta- quinti- lima
hexa- sexti- enam
hepta- septi- tujuh
octa- octi- delapan
nona- novi- sembilan
deca- deci- sepuluh
hemi- semi- setengah
hecto- centi- seratus
kilo- milli- seribu
poly- multi- banyak
pan- omni- semua
macro- maxi- besar
micro- mini- kecil
a- non- tidak
an- in-(un-) bukan
amphi- ambi- dua-duanya
iso- equi- sama
hyper- super- atas
hypo- sub- bawah
endo- intra- dalam
exo- extra- luar
ortho- cis- dekat
para- ultra- seberang
peri- circum- keliling
dia- trans- melalui
pra- pre- sebelum
meta- post- setelah
ana- pro- maju, pergi
cata- re- mundur, kembali
syn- co- bersama-sama
anti- contra- lawan
dis- de- hilang
hydro- aqua- air


AWALAN-AWALAN SATUAN

10(1) deka (da)
10(2) hekto (h)
10(3) kilo (k)
10(6) mega (M)
10(9) giga (G)
10(12) tera (T)
10(15) peta (P)
10(18) exa (E)
10(21) zetta (Z)
10(24) yotta (Y)

10(-1) deci (d)
10(-2) centi (c)
10(-3) milli (m)
10(-6) micro (m)
10(-9) nano (n)
10(-12) pico (p)
10(-15) femto (f)
10(-18) atto (a)
10(-21) zepto (z)
10(-24) yocto (y

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ISTILAH-ISTILAH PENTING DALAM KIMIA

agen pengoksidaan = zat pengoksidasi
agen penurunan = zat pereduksi
air liat = air sadah
ampaian = suspensi
bes = basa

campuran mesra = campuran homogen
campuran tak sekata = campuran heterogen
formula am = rumus umum
formula mudah = rumus empiris

gangsa = perunggu
gas adi = gas mulia
gas asli = gas alam
gas unggul = gas ideal
gelang benzena = cincin benzena
getah tiruan = karet sintetis
haba = kalor
haba tindakbalas = kalor reaksi
hasil darab keterlarutan = hasil kali kelarutan
hukum keabadian jisim = hukum kekekalan massa
jadual berkala = sistem periodik
kadar tindakbalas = laju reaksi
kakisan = korosi
keluli = baja
kepekatan = konsentrasi
kesan ion sepunya = pengaruh ion sejenis
kontang = anhidrat
kumpulan alkali bumi = golongan alkali tanah
larutan muak (tepu) = larutan jenuh
loyang = kuningan
mangkin = katalis
nombor pengoksidaan = bilangan oksidasi
pemendakan = pengendapan
pempolimeran penambahan = polimerisasi adisi
penapaian = peragian, fermentasi
penceraian = penguraian, disosiasi
pengimbangan tindakbalas = penyetaraan reaksi
penimbal = penyangga, buffer
penukargantian = substitusi
penunjuk = indikator
penunu Bunsen = pembakar Bunsen
penurunan = reduksi
penyingkiran = eliminasi
penyiringan = dekantasi
perendahan takat beku = penurunan titik beku
sebatian = senyawa
sebatian berkutub = senyawa polar
tatarajah elekron = konfigurasi elektron
tepu, muak = jenuh
tertib tindakbalas = orde reaksi
teruja = tereksitasi
tindakbalas = reaksi
unsur peralihan = unsur transisi
unsur wakilan = unsur utama
zarah asas = partikel dasar

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ETIMOLOGI UNSUR-UNSUR KIMIA

Sebaiknya kita mengenal sejarah, bagaimana pemberian nama untuk unsur-unsur kimia yang ada di alam. Bagian ini akan memberikan informasi etimologi dari beberapa unsur kimia yang sering kita jumpai .
Hidrogen, H (Yunani: hydor = air; genes = pembentuk}
Helium, He (Yunani: helios = matahari)
Karbon, C (Latin: carbo = batubara)

Litium , Li (Yunani: lithos = batu)
Berilium, Be (Latin: beryl = manis)
Boron, B (Arab: buraq = jernih)
Nitrogen, N (Yunani: nitron = basa; genes = pembentuk)
Oksigen, O (Yunani: oxys = asam; genes = pembentuk)
Fluor, F (Latin: fluere = mengalir)
Neon, Ne (Yunani: neos = baru)

Natrium, Na (Latin: natri = basa)
Magnesium, Mg (Magnesia, daerah di Yunani)
Aluminium, Al (Latin: alum = pahit)
Silikon, Si (Latin: silex = batu api)
Fosfor, P (Yunani: phosphoros = pembawa cahaya)
Belerang, S (Latin: sulphur = belerang)
Klor, Cl (Yunani: chloros = hijau)
Argon, Ar (Yunani: argos = malas)
Kalium, K (Arab: qali = abu)
Kalsium, Ca (Latin: calx = kapur)

Skandium, Sc (Skandinavia)
Titanium, Ti (Yunani: titan = besar tubuh, raksasa)
Vanadium, V (Vanadis, dewi cinta Skandinavia)
Krom, Cr (Yunani: chroma = warna)
Mangan, Mn (Latin: magnes = bermagnet)
Besi, Fe (Latin: ferrum = besi)
Kobal, Co (Jerman: kobold = ruh jahat)
Nikel, Ni (Jerman: kupfernickel = tembaga palsu)
Tembaga, Cu (Yunani: Kypros = Siprus)
Seng, Zn (Jerman: zink = seng)

Galium, Ga (Latin: Gallia = Perancis)
Germanium, Ge (Latin: Germania = Jerman)
Arsen, As (Arab: az-zirnikh = kuning emas)
Selenium, Se (Yunani: selene = bulan)
Brom, Br (Yunani: bromos = pesing)
Kripton, Kr (Yunani: kryptos = tersembunyi)
Rubidium, Rb (Latin: rubidus = merah)
Strontium, Sr (Strontian, daerah di Skotlandia)
Itrium, Y (Ytterby, daerah di Swedia)
Zirkonium, Zr (Arab: zarqun = kemilau)

Niobium, Nb (Niobe, dewi Yunani)
Molibdenium, Mo (Yunani: molybdos = timbal)
Teknesium, Tc (Yunani: technetos = buatan)
Rutenium, Ru (Latin: Ruthenia = Rusia)
Rodium, Rh (Yunani: rhodos = merah jambu)
Paladium, Pd (Asteroid Pallas)
Perak, Ag (Latin: argentum = perak)
Kadmium, Cd (Kadmos, raja Thebe di Yunani)
Indium, In (Latin: indicum = nila)
Timah, Sn (Latin: stannum = timah)

Antimon, Sb (Yunani: stibi = cincin)
Telurium, Te (Latin: tellus = tanah)
Iodium, I (Yunani: iodes = ungu)
Xenon, Xe (Yunani: xenos = asing)
Sesium, Cs (Latin: caesius = biru)
Barium, Ba (Yunani: baros = berat)
Lantanum, La (Yunani: lanthanein = tercecer)
Serium, Ce (Asteroid Ceres)
Praseodimium, Pr (Yunani: praseos = hijau tua; dymos = kembar)
Neodimium, Nd (Yunani: neos = baru; dymos = kembar)

Prometium, Pm (Prometheos, tokoh mitos Yunani)
Samarium, Sm (Kolonel Samarski, ahli tambang Rusia)
Eropium, Eu (Benua Eropa)
Gadolinium, Gd (Johan Gadolin, 1760-1852, orang Finlandia)
Terbium, Tb (Ytterby, daerah di Swedia)
Disprosium, Dy (Yunani: dysprositos = sukar didapat)
Holmium, Ho (Latin: Holmia = Stockholm)
Erbium, Er (Ytterby, daerah di Swedia)
Tulium, Tm (Yunani: Thule = Swedia)
Iterbium, Yb (Ytterby, daerah di Swedia)

Lutetium, Lu (Latin: Lutetia = Paris)
Hafnium, Hf (Latin: Hafnia = Kopenhagen)
Tantalum, Ta (Tantalus, dewa Yunani)
Wolfram, W (Jerman: wolfram = batu berat)
Renium, Re (Latin: Rhenus = Sungai Rhine)
Osmium, Os (Yunani: osme = bau)
Iridium, Ir (Latin: iris = pelangi)
Platina, Pt (Spanyol: platina = perak kecil)
Emas, Au (Latin: aurora = fajar)
Raksa, Hg (Yunani: hydrargyre = air perak)

Talium, Tl (Yunani: thallos = hijau muda)
Timbal, Pb (Latin: plumbum = timbal)
Bismut, Bi (Arab: bismuth = cerah)
Polonium, Po (Latin: Polonia = Polandia)
Astatin, At (Yunani: astatos = tidak tetap)
Radon, Rn (Latin: radius = sinar)
Fransium, Fr (Perancis)
Radium, Ra (Latin: radius = sinar)
Aktinium, Ac (Yunani: aktis = sinar)
Torium, Th (Thor, dewa Skandinavia)

Protaktinium, Pa (Yunani: pertama menjadi aktinium)
Uranium, U (Planet Uranus)
Neptunium, Np (Planet Neptunus)
Plutonium, Pu (Planet Pluto)
Amerisium, Am (Benua Amerika)
Kurium, Cm (Marie Sklodowska Curie, 1867-1934)
Berkelium, Bk (Berkeley di Amerika Serikat)
Kalifornium, Cf (California di Amerika Serikat)
Einsteinium, Es (Albert Einstein, 1879-1955)
Fermium, Fm (Enrico Fermi, 1901-1954)

Mendelevium, Md (Dmitri Ivanovich Mendeleyef, 1834-1907)
Nobelium, No (Alfred Bernhard Nobel, 1833-1896)
Lawrensium, Lr (Ernest Orlando Lawrence, 1901-1958)
Ruterfordium, Rf (Ernest Rutherford, 1871-1937)
Dubnium, Db (Dubna di Rusia)
Seaborgium, Sg (Glenn Theodore Seaborg, 1912-1999)
Bohrium, Bh (Niels Henry David Bohr, 1885-1962)
Hassium, Hs (Hasse di Jerman)
Meitnerium, Mt (Lise Meitner, 1878-1968)
Darmstadtium, Ds (Darmstadt di Jerman)

Rontgenium, Rg (Wilhelm Konrad Rontgen, 1845-1923)

Catatan:
IUPAC menetapkan bahwa sejak unsur nomor atom 96, nama unsur mengabadikan nama ilmuwan atau nama tempat penelitian unsur.
Unsur-unsur ununbium (112, Uub), ununtrium (113, Uut), ununquadium (114, Uuq), ununpentium (115, Uup), dan ununhexium (116, Uuh) sudah berhasil disintesis, tapi belum diberi nama resmi oleh IUPAC.

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Kembang Api

Membuat warna warni kembang api bukanlah suatu usaha yang mudah. Hal tersebut memerlukan pertimbangan baik dari segi seni dan juga aplikasi ilmu fisika. Cahaya yang dikeluarkan oleh kembang api secara umum memerlukan zat penghasil oksigen, bahan bakar, pengikat (binder), dan bahan Membuat warna warni kembang api bukanlah suatu usaha yang mudah.

Hal tersebut memerlukan pertimbangan baik dari segi seni dan juga aplikasi ilmu fisika. Cahaya yang dikeluarkan oleh kembang api secara umum memerlukan zat penghasil oksigen, bahan bakar, pengikat (binder), dan bahan penghasil warna. Ada dua mekanisme utama pembentukan warna dalam kembang api, yaitu incandescence dan luminescence.

Incandescence adalah cahaya yang dihasilkan dari proses pemanasan. Proses tersebut akan menyebabkan suatu bahan menjadi panas dan menyala. Pada awalnya akan mengeluarkan cahaya inframerah, kemudian berubah menjadi merah, oranye, kuning, dan putih. Perubahan-perubahan warna tersebut terjadi seiiring dengan bertambah panasnya suatu bahan. Jika suhu kembang api dapat dikontrol, nyala dari komponen atau bahan, misalnya arang, dapat dimanipulasi menjadi warna yang kita inginkan. Logam-logam seperti aluminium, magnesium, dan titanium terbakar dengan nyala yang sangat terang sehingga dapat digunakan untuk meningkatkan suhu kembang api yang pada akhirnya dapat menghasilkan perubahan perubahan warna cahaya kembang api yang sangat menarik.

Luminiscence adalah cahaya yang dihasilkan menggunakan sumber energi selain panas. Kadang-kadang luminescence disebut juga dengan cahaya dingin karena ia dapat terjadi pada suhu ruang bahkan pada suhu yang lebih rendah. Untuk menghasilkan luminescence, energi diserap oleh elektron suatu atom atau molekul. Hal tersebut menyebabkan elektron berada dalam keadaan tereksitasi dan tidak stabil. Kemudian, ketika elektron kembali ke energi yang lebih rendah, ia akan melepas energi dalam bentuk foton (cahaya). Energi foton tersebut akan menentukan panjang gelombang atau cahaya di keluarkan.
Kadang-kadang senyawaan gram yang diperlukan untuk menghasilkan warna yang diinginkan tidak stabil pada kondisi tertentu. Barium klorida, yang biasanya dipakai untuk menghasilkan warna hijau, tidak stabil pada suhu ruang. Untuk mengatasi hal tersebut, barium harus dikombinasikan dengan senyawa yang lebih stabil, misalnya klorin. Dalam hal ini, klorin dilepaskan ke dalam panas untuk kemudian bereaksi dengan barium sehingga membentuk barium klorida yang menghasilkan warna hijau. Sebaliknya tembaga klorida (biru) tidak stabil pada suhu tinggi sehingga kembang api perlu didesain untuk tidak terlalu panas tetapi cukup terang untuk di lihat.

Kualitas
Kualitas warna kembang api ditentukan oleh kemurnian bahan yang dipakai. Semakin murni bahannya, maka akan semakin baik pula warna warni yang dihasilkan. Gangguan dari garam natrium (kuning-orange) walaupun dalam jumlah yang kecil, dapat mengalahkan warna lain yang diharapkan. Komposisi bahan-bahan yang dipakai untuk membuat kembang api juga perlu diperhatikan agar tidak menghasilkan terlalu banyak asap yang dapat menutupi warna-warni yg dipancarkan. Tentu juga secara ekonomi, harga-harga bahan akan mempengaruhi kualitas kembang api juga. Skill pembuatnya dan waktu/kapan kembang api tersebut dibuat akan sangat berpengaruh besar terhadap hasil akhir kembang api.

Beberapa contoh senyawa penghasil warna kembang api tertera pada tabel di bawah ini:

Warna Senyawa
Merah garam-garam stronsium dan litium
litium karbonat = merah
stronsium karbonat = merah terang
Orange garam-gram kalsium
kalsium klorida
kalsium sulfat
Kuning - Emas incandescence besi-karbon, arang
Kuning Senyawaan natrium
natrium nitrat
kriolit (Na3AlF6)
Putih neon magnesium , aluminium, barium oksida
Hijau Senyawa barium + klorin
Biru Senyawaan tembaga + klorin
tembaga asetoarsenit = biru
tembaga klorida = biru pirus
Ungu campuran senyawa-senyawa stronsium (merah) dengan tembaga (biru)
Perak pembakaran aluminium, titanium, atau magnesium powder

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The Periodic Table

Select the elements you wish to work with in the PERIODIC TABLE window by clicking individual element buttons or labeled buttons that select categories of elements.
To make a graph, in the GRAPH window, select the property you wish to plot on the x–axis from the X menu and the property you wish to plot on the y–axis from the Y menu. The graph appears automatically.

To use the sorting table, in the TABLE window, select the properties that interest you from the TABLE FIELDS menu. You can select up to 3 properties. Click a column header to sort the information by the data in that column.
Detailed information about each of the windows and the options and features they contain is found below.

PERIODIC TABLE Window
The PERIODIC TABLE window, located in the upper left corner of the browser window, is the heart of the applet. It is illustrated in Figure 2.1. Only data for the elements selected in the PERIODIC TABLE window are displayed in the GRAPH and TABLE windows. The PERIODIC TABLE window contains a standard periodic table (elements 1 through 112), as well as buttons that can be used to select or deselect elements. Elements can also be selected or deselected by performing a search in the GRAPH and TABLE windows. See the sections of the documentation on Searching in the GRAPH or TABLE window for more information.
Figure 2.1 – The PERIODIC TABLE window is used to select elements used in the TABLE and GRAPH windows.The elements Zn, Ga, Ge, As, Se, Br and Kr are selected and all other elements are deselected.
Each element in the periodic table is a button. Clicking one of these buttons will select or deselect the element. When the applet starts, all elements are selected (see Fig. 1.1).
Buttons for selected elements appear darker than those of deselected elements. In the Figure 2.1, the elements Zn, Ga, Ge, As, Se, Br and Kr are selected and all other elements are deselected.
An element’s name and atomic number can be displayed in a pop–up label by positioning the mouse cursor over the element button. The pop-up label for germanium (Ge) is displayed in Figure 2.1.
All of the other buttons in the PERIODIC TABLE window are used to select or deselect categories of elements. On the left–hand side of each period (row) in the periodic table is a numbered button that will either select or deselect all of the elements in that period. Similarly, at the top of each group (column), there is a numbered button that will either select or deselect all of the elements in that group. The buttons labeled MAIN GROUP ELEMENTS, TRANSITION METALS, and INNER TRANSITION METALS select or deselect the corresponding elements. If none or only some of the elements in a category are selected, are selected, clicking one of these buttons selects all of the elements in the category. Only if all of the elements in that category are already selected will clicking one of these buttons result in deselecting the elements.
The toolbar at the top of the PERIODIC TABLE window contains five additional buttons. These buttons can be used to select all of the elements in the periodic table (Select All), deselect all of the elements (Deselect All), select all of the metals (Select Metals), select all of the non-metals (Select Non-Metals ), and select all of the semi–metals (Select Semi–Metals).

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Sorbitol : Sweetener syntetic

Sorbitol is used in "sugar-free" mints and various cough syrups and is usually listed under the inactive ingredients.

Sorbitol is a

sugar substitute often used in diet foods (including diet drinks and ice cream) and sugar-free chewing gum. It also occurs naturally in many stone fruits and berries from trees of the genus Sorbus. Sorbitol is also referred to as a nutritive sweetener because it provides dietary energy: 2.6 kilocalories (11 kilojoules) per gram versus the average 4 kilocalories (17 kJ) of sugar and starch, while retaining 60% of the sweetness.[citation needed] As a food additive it has an E number E420, categorized as a sweetener, emulsifier and humectant.
Laxative
Sorbitol can be used as a non-stimulant laxative as either an oral suspension or suppository. The drug works by drawing water into the large intestine, thereby stimulating bowel movements. Sorbitol has been determined safe to use in the elderly although it is by no means recommended.

Miscellaneous
Sorbitol is often used in modern cosmetics as a humectant and thickener. Some transparent gels can only be made with sorbitol as it has a refractive index sufficiently high for transparent formulations. It is also used as a humectant in some cigarettes.
Sorbitol is used as a cryoprotectant additive (mixed with sucrose and sodium polyphosphates) in the manufacture of surimi, a highly refined, uncooked fish paste most commonly produced from Alaska (or walleye) pollock (Theragra chalcogramma).
Furthermore, Sorbitol, combined with Kayexalate, helps the body rid itself of excess potassium ions in a hyperkalaemic state. The Kayexalate exchanges sodium ions for potassium ions in the bowel, while sorbitol helps to eliminate it.[citation needed]
Sorbitol when combined with potassium nitrate has found some success as an amateur solid rocket fuel.
Sorbitol is often used in Mouthwash, as it said that when mixed with other certain ingredients it can help fight plaque.
Sorbitol is identified as a potential key chemical intermediate from biomass resources. Complete reduction of sorbitol opens the way to alkanes such as hexane which can be used as a biofuel. Sorbitol itself provides much of the hydrogen required for the transformation.
19 C6O6H14 → 13 C6H14 + 36 CO2 + 42 H2O
The above chemical reaction is exothermic and 1.5 mole of sorbitol generates 1 mole of hexane. When hydrogen is co-fed, no carbon dioxide production takes place.
Overdose effects
Ingesting large amounts of sorbitol can lead to some abdominal pain, gas, and mild to severe diarrhea. Sorbitol ingestion of 20g/d as sugar-free gum has led to severe diarrhea leading to unintended weight loss of 24 lbs in an 114 lb woman; another patient required hospitalization after habitually consuming 30g/d. Sorbitol can also aggravate irritable bowel syndrome and fructose malabsorption. Even in the absence of dietary sorbitol, cells also produce sorbitol naturally. When too much sorbitol is produced inside cells, it can cause damage. Diabetic retinopathy and neuropathy may be related to excess sorbitol in the cells of the eyes and nerves. The source of this sorbitol in diabetics is excess glucose, which goes through the polyol pathway

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Sorbitol

Sorbitol is a bulk sweetener with good taste and reduced calories. It does not promote tooth decay. Sorbitol is suitable for a variety of products reduced in calories, sugar or fat and has been safely used for almost half a century.

Sorbitol, a polyol (sugar alcohol), is a bulk sweetener found in numerous food products. In addition to providing sweetness, it is an excellent humectant and texturizing agent. Sorbitol is about 60 percent as sweet as sucrose with one-third fewer calories. It has a smooth mouthfeel with a sweet, cool and pleasant taste. It is non-cariogenic and may be useful to people with diabetes. Sorbitol has been safely used in processed foods for almost half a century. It is also used in other products, such as pharmaceuticals and cosmetics. A French chemist first discovered sorbitol in the berries of the mountain ash in 1872. It occurs naturally in a wide variety of fruits and berries. Today it is commercially produced by the hydrogenation of glucose and is available in both liquid and crystalline form. Sorbitol has been affirmed as GRAS (Generally Recognized As Safe) by the U.S. Food and Drug Administration and is approved for use by the European Union and numerous countries around the world, including Australia, Canada and Japan. In the United States, sorbitol is provided by a number of manufacturers, including Archer Daniels Midland, Cargill Inc., Roquette America, Inc. and SPI Polyols, Inc.
Functional Advantages Sorbitol is used as a humectant in many types of products for protection against loss of moisture content. The moisture-stabilizing and textural properties of sorbitol are used in the production of confectionery, baked goods and chocolate where products tend to become dry or harden. Its moisture-stabilizing action protects these products from drying and maintains their initial freshness during storage. Sorbitol is very stable and chemically unreactive. It can withstand high temperatures and does not participate in Maillard (browning) reactions. This is an advantage, for example, in the production of cookies where a fresh color with no appearance of browning is desired. Sorbitol also combines well with other food ingredients such as sugars, gelling agents, proteins and vegetable fats. It functions well in many food products such as chewing gums, candies, frozen desserts, cookies, cakes, icings and fillings as well as oral care products, including toothpaste and mouthwash.
Sorbitol
Provides bulk and sweetness with a clean, cool pleasant taste
Provides one-third fewer calories than sugar--about 2.6 calories per gram
Is an excellent humectant, texturizing and anti-crystallizing agent
Can be used in a wide variety of products, including sugar-free candies, chewing gums, frozen desserts and baked goods
Does not contribute to the formation of dental caries
May be useful as an alternative to sugar for people with diabetes on the advice of their health care providers
Does Not Promote Tooth Decay Polyols, including sorbitol, are resistant to metabolism by oral bacteria which break down sugars and starches to release acids that may lead to cavities or erode tooth enamel. They are, therefore, non-cariogenic. The usefulness of polyols, including sorbitol, as alternatives to sugars and as part of a comprehensive program including proper dental hygiene has been recognized by the American Dental Association. The FDA has approved the use of a "does not promote tooth decay" health claim in labeling for sugar-free foods that contain sorbitol or other polyols.
Use In The Diets Of People With Diabetes Control of blood glucose, lipids and weight are the three major goals of diabetes management today. Sorbitol is slowly absorbed. Therefore, when sorbitol is used, the rise in blood glucose and the insulin response associated with the ingestion of glucose is significantly reduced. The reduced caloric value (2.6 calories per gram versus 4.0 for sugar) of sorbitol is consistent with the objective of weight control. Products sweetened with sorbitol in place of sugar may be useful in providing a wider variety of reduced calorie and sugar free choices to people with diabetes. Recognizing that diabetes is complex and requirements for its management may vary between individuals, the usefulness of sorbitol should be discussed between individuals and their health care providers. Foods sweetened with sorbitol may contain other ingredients which also contribute calories and other nutrients. These must be considered in meal planning.
Reduced Calorie Alternative To Sugar Absorption of sorbitol by the human body is slow, allowing part of the ingested sorbitol to reach the large intestine where metabolism yields fewer calories. Therefore, unlike sugar which contributes four calories per gram, the caloric contribution of sorbitol is about 2.6 calories per gram. The U.S. Food and Drug Administration has stated it does not object to the use of this value. For a product to qualify as “reduced calorie” in the United States, it must have at least a 25 percent reduction in calories; to qualify as “light” it must have a one-third reduction. Sorbitol is, therefore, useful in formulating “reduced calorie” and “light” products. The lower caloric value of sorbitol and other polyols is recognized in other countries as well. For example, the European Union has provided a Nutritional Labeling Directive stating that all polyols, including sorbitol, have a caloric value of 2.4 calories per gram.
Safety Sorbitol’s safety is supported by numerous studies reported in the scientific literature. In developing the current U.S. food and drug regulation which affirms sorbitol as GRAS, the safety data were carefully evaluated by qualified scientists of the Select Committee on GRAS Substances selected by the Life Sciences Office of the Federation of American Societies for Experimental Biology (FASEB). In the opinion of the Select Committee, there was no evidence demonstrating a hazard where sorbitol was used at current levels or at levels that might be expected in the future. The U.S. Food and Drug Administration’s regulation for sorbitol requires the following label statement for foods whose reasonably foreseeable consumption may result in the daily ingestion of 50 grams of sorbitol: “Excess consumption may have a laxative effect.” The Joint Food and Agriculture Organization/World Health Organization Expert Committee on Food Additives (JECFA) has reviewed the safety data and concluded that sorbitol is safe. JECFA has established an acceptable daily intake (ADI) for sorbitol of “not specified,” meaning no limits are placed on its use. An ADI “not specified” is the safest category in which JECFA can place a food ingredient. JECFA’s decisions are often adopted by many small countries which do not have their own agencies to review food additive safety. The Scientific Committee for Food of the European Union (EU) published a comprehensive assessment of sweeteners in 1985, concluding that sorbitol is acceptable for use, also without setting a limit on its use.
Multiple Ingredient Approach To Calorie Control Americans continue to demand good tasting products with less calories and fat. The development and use of a variety of safe low-calorie sweeteners, bulking agents, fat replacers and other low-calorie ingredients help meet this consumer demand. The availability of several low-calorie ingredients allows food manufacturers to choose the most appropriate ingredient, or combination of ingredients, for a given product. Sorbitol works well with other ingredients and may be synergistic with other sweeteners. This means the combination of the sweeteners is sweeter than the sum of the individual sweeteners and results in synergistic blends which provide taste, economic and stability advantages.
Future Sorbitol’s good taste, reduced caloric value, versatility and other advantages facilitate its use in a wide variety of products. With the increasing demand for products reduced in calories or fat, sorbitol’s use should increase as wel

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THE SCIENTIFIC ENTERPRISE

Science as an enterprise has individual, social, and institutional dimensions. Scientific activity is one of the main features of the contemporary world and, perhaps more than any other, distinguishes our times from earlier centuries.
Science Is a Complex Social Activity

Scientific work involves many individuals doing many different kinds of work and goes on to some degree in all nations of the world. Men and women of all ethnic and national backgrounds participate in science and its applications. These people—scientists and engineers, mathematicians, physicians, technicians, computer programmers, librarians, and others—may focus on scientific knowledge either for its own sake or for a particular practical purpose, and they may be concerned with data gathering, theory building, instrument building, or communicating.

As a social activity, science inevitably reflects social values and viewpoints. The history of economic theory, for example, has paralleled the development of ideas of social justice—at one time, economists considered the optimum wage for workers to be no more than what would just barely allow the workers to survive. Before the twentieth century, and well into it, women and people of color were essentially excluded from most of science by restrictions on their education and employment opportunities; the remarkable few who overcame those obstacles were even then likely to have their work belittled by the science establishment.

The direction of scientific research is affected by informal influences within the culture of science itself, such as prevailing opinion on what questions are most interesting or what methods of investigation are most likely to be fruitful. Elaborate processes involving scientists themselves have been developed to decide which research proposals receive funding, and committees of scientists regularly review progress in various disciplines to recommend general priorities for funding.

Science goes on in many different settings. Scientists are employed by universities, hospitals, business and industry, government, independent research organizations, and scientific associations. They may work alone, in small groups, or as members of large research teams. Their places of work include classrooms, offices, laboratories, and natural field settings from space to the bottom of the sea.

Because of the social nature of science, the dissemination of scientific information is crucial to its progress. Some scientists present their findings and theories in papers that are delivered at meetings or published in scientific journals. Those papers enable scientists to inform others about their work, to expose their ideas to criticism by other scientists, and, of course, to stay abreast of scientific developments around the world. The advancement of information science (knowledge of the nature of information and its manipulation) and the development of information technologies (especially computer systems) affect all sciences. Those technologies speed up data collection, compilation, and analysis; make new kinds of analysis practical; and shorten the time between discovery and application.
Science Is Organized Into Content Disciplines and Is Conducted in Various Institutions

Organizationally, science can be thought of as the collection of all of the different scientific fields, or content disciplines. From anthropology through zoology, there are dozens of such disciplines. They differ from one another in many ways, including history, phenomena studied, techniques and language used, and kinds of outcomes desired. With respect to purpose and philosophy, however, all are equally scientific and together make up the same scientific endeavor. The advantage of having disciplines is that they provide a conceptual structure for organizing research and research findings. The disadvantage is that their divisions do not necessarily match the way the world works, and they can make communication difficult. In any case, scientific disciplines do not have fixed borders. Physics shades into chemistry, astronomy, and geology, as does chemistry into biology and psychology, and so on. New scientific disciplines (astrophysics and sociobiology, for instance) are continually being formed at the boundaries of others. Some disciplines grow and break into subdisciplines, which then become disciplines in their own right.

Universities, industry, and government are also part of the structure of the scientific endeavor. University research usually emphasizes knowledge for its own sake, although much of it is also directed toward practical problems. Universities, of course, are also particularly committed to educating successive generations of scientists, mathematicians, and engineers. Industries and businesses usually emphasize research directed to practical ends, but many also sponsor research that has no immediately obvious applications, partly on the premise that it will be applied fruitfully in the long run. The federal government funds much of the research in universities and in industry but also supports and conducts research in its many national laboratories and research centers. Private foundations, public-interest groups, and state governments also support research.

Funding agencies influence the direction of science by virtue of the decisions they make on which research to support. Other deliberate controls on science result from federal (and sometimes local) government regulations on research practices that are deemed to be dangerous and on the treatment of the human and animal subjects used in experiments.
There Are Generally Accepted Ethical Principles in the Conduct of Science

Most scientists conduct themselves according to the ethical norms of science. The strongly held traditions of accurate recordkeeping, openness, and replication, buttressed by the critical review of one's work by peers, serve to keep the vast majority of scientists well within the bounds of ethical professional behavior. Sometimes, however, the pressure to get credit for being the first to publish an idea or observation leads some scientists to withhold information or even to falsify their findings. Such a violation of the very nature of science impedes science. When discovered, it is strongly condemned by the scientific community and the agencies that fund research.

Another domain of scientific ethics relates to possible harm that could result from scientific experiments. One aspect is the treatment of live experimental subjects. Modern scientific ethics require that due regard must be given to the health, comfort, and well-being of animal subjects. Moreover, research involving human subjects may be conducted only with the informed consent of the subjects, even if this constraint limits some kinds of potentially important research or influences the results. Informed consent entails full disclosure of the risks and intended benefits of the research and the right to refuse to participate. In addition, scientists must not knowingly subject coworkers, students, the neighborhood, or the community to health or property risks without their knowledge and consent.

The ethics of science also relates to the possible harmful effects of applying the results of research. The long-term effects of science may be unpredictable, but some idea of what applications are expected from scientific work can be ascertained by knowing who is interested in funding it. If, for example, the Department of Defense offers contracts for working on a line of theoretical mathematics, mathematicians may infer that it has application to new military technology and therefore would likely be subject to secrecy measures. Military or industrial secrecy is acceptable to some scientists but not to others. Whether a scientist chooses to work on research of great potential risk to humanity, such as nuclear weapons or germ warfare, is considered by many scientists to be a matter of personal ethics, not one of professional ethics.
Scientists Participate in Public Affairs Both as Specialists and as Citizens

Scientists can bring information, insights, and analytical skills to bear on matters of public concern. Often they can help the public and its representatives to understand the likely causes of events (such as natural and technological disasters) and to estimate the possible effects of projected policies (such as ecological effects of various farming methods). Often they can testify to what is not possible. In playing this advisory role, scientists are expected to be especially careful in trying to distinguish fact from interpretation, and research findings from speculation and opinion; that is, they are expected to make full use of the principles of scientific inquiry.

Even so, scientists can seldom bring definitive answers to matters of public debate. Some issues are too complex to fit within the current scope of science, or there may be little reliable information available, or the values involved may lie outside of science. Moreover, although there may be at any one time a broad consensus on the bulk of scientific knowledge, the agreement does not extend to all scientific issues, let alone to all science-related social issues. And of course, on issues outside of their expertise, the opinions of scientists should enjoy no special credibility.

In their work, scientists go to great lengths to avoid bias—their own as well as that of others. But in matters of public interest, scientists, like other people, can be expected to be biased where their own personal, corporate, institutional, or community interests are at stake. For example, because of their commitment to science, many scientists may understandably be less than objective in their beliefs on how science is to be funded in comparison to other social needs.

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Markovnikov's rule

In chemistry, Markovnikov's rule or Markownikoff's rule is an observation based on Zaitsev's rule. It was formulated by the Russian chemist Vladimir Vasilevich Markovnikov in 1870 .

In chemical reactions found particularly in organic chemistry, the rule states that with the addition of H-X to an alkene, the acid hydrogen (H) becomes attached to the carbon with the greatest number of hydrogens, and the halide (X) group becomes attached to the carbon with the fewest hydrogens
Markovnikov's rule is illustrated by the reaction of Propene with HBr, major product shown.The same is true when an alkene reacts with water in an addition reaction to form alcohol. The hydroxyl group (OH) bonds to the carbon that has the greater number of carbon-carbon bonds, while the hydrogen bonds to the carbon on the other end of the double bond, that has more carbon-hydrogen bonds.
The chemical basis for Markovnikov's Rule is the formation of the most stable carbocation during the addition process. The addition of the hydrogen to one carbon atom in the alkene creates a positive charge on the other carbon, forming a carbocation intermediate. The more substituted the carbocation (the more bonds it has to carbon or to electron-donating substituents) the more stable it is, due to induction and hyperconjugation. The major product of the addition reaction will be the one formed from the more stable intermediate. Therefore, the major product of the addition of HX (where X is some atom more electronegative than H) to an alkene has the hydrogen atom in the less substituted position and X in the more substituted position. It is important to note, however, that the other less substituted, less stable carbocation will still be formed to some degree, and will proceed to form the minor product with the opposite attachment of X.
The rule may be summarized as "the rich get richer and the poor get poorer" or "thems as has, gits" (The "West Virginia" version): a carbon rich in substituents will gain more substituents and the carbon with more hydrogens attached will get the hydrogen in many organic addition reactions.
One of the organic reactions Markovnikov based his rule on (first performed in 1865) was that of hydrogen iodide with vinyl bromide. In another manifestation of his rule he observed that the halogen atom added to the carbon atom already carrying a halogen atom Geminal halide hydrolysis of the initial reaction product with moist or hydrogenated (rarely used) silver oxide to ethanal proved the 1,1 substitution pattern.

It has been observed that the original 1869 Markovnikov publication was sloppy and that he did not do much experimental work himself. The rule itself appeared only as a four-page footnote in a 26-page article, which may also explain why his rule took 60 years to be accepted.
Anti Markovnikov rule
Mechanisms which avoid the carbocation intermediate may react through other mechanisms that are regioselective, against what Markovnikov's rule predicts, such as free radical addition. Such reactions are said to be anti-Markovnikov, since the halogen adds to the less substituted carbon.This reaction is exactly opposite of Markovnikov reaction,and hence the name. Again, like the positive charge, the radical is most stable when in the more substituted position.
Anti-Markovnikov behaviour extends to other chemical reactions than just additions to alkenes. One Anti-Markovnikov manifestation is observed in hydration of phenylacetylene that, gold-catalyzed, gives regular acetophenone but with a special ruthenium catalyst the other regioisomer 2-phenylacetaldehyde.

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SCIENTIFIC INQUIRY

Fundamentally, the various scientific disciplines are alike in their reliance on evidence, the use of hypothesis and theories, the kinds of logic used, and much more. Nevertheless, scientists differ greatly from one another in what phenomena they investigate and in how they go about their work; in the reliance they place on historical data or on experimental findings and on qualitative or quantitative methods; in their recourse to fundamental principles; and in how much they draw on the findings of other sciences. Still, the exchange of techniques, information, and concepts goes on all the time among scientists, and there are common understandings among them about what constitutes an investigation that is scientifically valid.

Scientific inquiry is not easily described apart from the context of particular investigations. There simply is no fixed set of steps that scientists always follow, no one path that leads them unerringly to scientific knowledge. There are, however, certain features of science that give it a distinctive character as a mode of inquiry. Although those features are especially characteristic of the work of professional scientists, everyone can exercise them in thinking scientifically about many matters of interest in everyday life.
Science Demands Evidence

Sooner or later, the validity of scientific claims is settled by referring to observations of phenomena. Hence, scientists concentrate on getting accurate data. Such evidence is obtained by observations and measurements taken in situations that range from natural settings (such as a forest) to completely contrived ones (such as the laboratory). To make their observations, scientists use their own senses, instruments (such as microscopes) that enhance those senses, and instruments that tap characteristics quite different from what humans can sense (such as magnetic fields). Scientists observe passively (earthquakes, bird migrations), make collections (rocks, shells), and actively probe the world (as by boring into the earth's crust or administering experimental medicines).

In some circumstances, scientists can control conditions deliberately and precisely to obtain their evidence. They may, for example, control the temperature, change the concentration of chemicals, or choose which organisms mate with which others. By varying just one condition at a time, they can hope to identify its exclusive effects on what happens, uncomplicated by changes in other conditions. Often, however, control of conditions may be impractical (as in studying stars), or unethical (as in studying people), or likely to distort the natural phenomena (as in studying wild animals in captivity). In such cases, observations have to be made over a sufficiently wide range of naturally occurring conditions to infer what the influence of various factors might be. Because of this reliance on evidence, great value is placed on the development of better instruments and techniques of observation, and the findings of any one investigator or group are usually checked by others.
Science Is a Blend of Logic and Imagination

Although all sorts of imagination and thought may be used in coming up with hypotheses and theories, sooner or later scientific arguments must conform to the principles of logical reasoning—that is, to testing the validity of arguments by applying certain criteria of inference, demonstration, and common sense. Scientists may often disagree about the value of a particular piece of evidence, or about the appropriateness of particular assumptions that are made—and therefore disagree about what conclusions are justified. But they tend to agree about the principles of logical reasoning that connect evidence and assumptions with conclusions.

Scientists do not work only with data and well-developed theories. Often, they have only tentative hypotheses about the way things may be. Such hypotheses are widely used in science for choosing what data to pay attention to and what additional data to seek, and for guiding the interpretation of data. In fact, the process of formulating and testing hypotheses is one of the core activities of scientists. To be useful, a hypothesis should suggest what evidence would support it and what evidence would refute it. A hypothesis that cannot in principle be put to the test of evidence may be interesting, but it is not likely to be scientifically useful.

The use of logic and the close examination of evidence are necessary but not usually sufficient for the advancement of science. Scientific concepts do not emerge automatically from data or from any amount of analysis alone. Inventing hypotheses or theories to imagine how the world works and then figuring out how they can be put to the test of reality is as creative as writing poetry, composing music, or designing skyscrapers. Sometimes discoveries in science are made unexpectedly, even by accident. But knowledge and creative insight are usually required to recognize the meaning of the unexpected. Aspects of data that have been ignored by one scientist may lead to new discoveries by another.
Science Explains and Predicts

Scientists strive to make sense of observations of phenomena by constructing explanations for them that use, or are consistent with, currently accepted scientific principles. Such explanations—theories—may be either sweeping or restricted, but they must be logically sound and incorporate a significant body of scientifically valid observations. The credibility of scientific theories often comes from their ability to show relationships among phenomena that previously seemed unrelated. The theory of moving continents, for example, has grown in credibility as it has shown relationships among such diverse phenomena as earthquakes, volcanoes, the match between types of fossils on different continents, the shapes of continents, and the contours of the ocean floors.

The essence of science is validation by observation. But it is not enough for scientific theories to fit only the observations that are already known. Theories should also fit additional observations that were not used in formulating the theories in the first place; that is, theories should have predictive power. Demonstrating the predictive power of a theory does not necessarily require the prediction of events in the future. The predictions may be about evidence from the past that has not yet been found or studied. A theory about the origins of human beings, for example, can be tested by new discoveries of human-like fossil remains. This approach is clearly necessary for reconstructing the events in the history of the earth or of the life forms on it. It is also necessary for the study of processes that usually occur very slowly, such as the building of mountains or the aging of stars. Stars, for example, evolve more slowly than we can usually observe. Theories of the evolution of stars, however, may predict unsuspected relationships between features of starlight that can then be sought in existing collections of data about stars.
Scientists Try to Identify and Avoid Bias

When faced with a claim that something is true, scientists respond by asking what evidence supports it. But scientific evidence can be biased in how the data are interpreted, in the recording or reporting of the data, or even in the choice of what data to consider in the first place. Scientists' nationality, sex, ethnic origin, age, political convictions, and so on may incline them to look for or emphasize one or another kind of evidence or interpretation. For example, for many years the study of primates—by male scientists—focused on the competitive social behavior of males. Not until female scientists entered the field was the importance of female primates' community-building behavior recognized.

Bias attributable to the investigator, the sample, the method, or the instrument may not be completely avoidable in every instance, but scientists want to know the possible sources of bias and how bias is likely to influence evidence. Scientists want, and are expected, to be as alert to possible bias in their own work as in that of other scientists, although such objectivity is not always achieved. One safeguard against undetected bias in an area of study is to have many different investigators or groups of investigators working in it.
Science Is Not Authoritarian

It is appropriate in science, as elsewhere, to turn to knowledgeable sources of information and opinion, usually people who specialize in relevant disciplines. But esteemed authorities have been wrong many times in the history of science. In the long run, no scientist, however famous or highly placed, is empowered to decide for other scientists what is true, for none are believed by other scientists to have special access to the truth. There are no preestablished conclusions that scientists must reach on the basis of their investigations.

In the short run, new ideas that do not mesh well with mainstream ideas may encounter vigorous criticism, and scientists investigating such ideas may have difficulty obtaining support for their research. Indeed, challenges to new ideas are the legitimate business of science in building valid knowledge. Even the most prestigious scientists have occasionally refused to accept new theories despite there being enough accumulated evidence to convince others. In the long run, however, theories are judged by their results: When someone comes up with a new or improved version that explains more phenomena or answers more important questions than the previous version, the new one eventually takes its place.

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THE NATURE OF SCIENCE

Over the course of human history, people have developed many interconnected and validated ideas about the physical, biological, psychological, and social worlds. Those ideas have enabled successive generations to achieve an increasingly comprehensive and reliable understanding of the human species and its environment.

The means used to develop these ideas are particular ways of observing, thinking, experimenting, and validating. These ways represent a fundamental aspect of the nature of science and reflect how science tends to differ from other modes of knowing.

It is the union of science, mathematics, and technology that forms the scientific endeavor and that makes it so successful. Although each of these human enterprises has a character and history of its own, each is dependent on and reinforces the others. Accordingly, the first three chapters of recommendations draw portraits of science, mathematics, and technology that emphasize their roles in the scientific endeavor and reveal some of the similarities and connections among them.

This chapter lays out recommendations for what knowledge of the way science works is requisite for scientific literacy. The chapter focuses on three principal subjects: the scientific world view, scientific methods of inquiry, and the nature of the scientific enterprise. Chapters 2 and 3 consider ways in which mathematics and technology differ from science in general. Chapters 4 through 9 present views of the world as depicted by current science; Chapter 10, Historical Perspectives, covers key episodes in the development of science; and Chapter 11, Common Themes, pulls together ideas that cut across all these views of the world.


THE SCIENTIFIC WORLD VIEW

Scientists share certain basic beliefs and attitudes about what they do and how they view their work. These have to do with the nature of the world and what can be learned about it.
The World Is Understandable

Science presumes that the things and events in the universe occur in consistent patterns that are comprehensible through careful, systematic study. Scientists believe that through the use of the intellect, and with the aid of instruments that extend the senses, people can discover patterns in all of nature.

Science also assumes that the universe is, as its name implies, a vast single system in which the basic rules are everywhere the same. Knowledge gained from studying one part of the universe is applicable to other parts. For instance, the same principles of motion and gravitation that explain the motion of falling objects on the surface of the earth also explain the motion of the moon and the planets. With some modifications over the years, the same principles of motion have applied to other forces—and to the motion of everything, from the smallest nuclear particles to the most massive stars, from sailboats to space vehicles, from bullets to light rays.
Scientific Ideas Are Subject To Change

Science is a process for producing knowledge. The process depends both on making careful observations of phenomena and on inventing theories for making sense out of those observations. Change in knowledge is inevitable because new observations may challenge prevailing theories. No matter how well one theory explains a set of observations, it is possible that another theory may fit just as well or better, or may fit a still wider range of observations. In science, the testing and improving and occasional discarding of theories, whether new or old, go on all the time. Scientists assume that even if there is no way to secure complete and absolute truth, increasingly accurate approximations can be made to account for the world and how it works.
Scientific Knowledge Is Durable

Although scientists reject the notion of attaining absolute truth and accept some uncertainty as part of nature, most scientific knowledge is durable. The modification of ideas, rather than their outright rejection, is the norm in science, as powerful constructs tend to survive and grow more precise and to become widely accepted. For example, in formulating the theory of relativity, Albert Einstein did not discard the Newtonian laws of motion but rather showed them to be only an approximation of limited application within a more general concept. (The National Aeronautics and Space Administration uses Newtonian mechanics, for instance, in calculating satellite trajectories.) Moreover, the growing ability of scientists to make accurate predictions about natural phenomena provides convincing evidence that we really are gaining in our understanding of how the world works. Continuity and stability are as characteristic of science as change is, and confidence is as prevalent as tentativeness.
Science Cannot Provide Complete Answers to All Questions

There are many matters that cannot usefully be examined in a scientific way. There are, for instance, beliefs that—by their very nature—cannot be proved or disproved (such as the existence of supernatural powers and beings, or the true purposes of life). In other cases, a scientific approach that may be valid is likely to be rejected as irrelevant by people who hold to certain beliefs (such as in miracles, fortune-telling, astrology, and superstition). Nor do scientists have the means to settle issues concerning good and evil, although they can sometimes contribute to the discussion of such issues by identifying the likely consequences of particular actions, which may be helpful in weighing alternatives.

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