282 WHAT 18 LIFE 



tive analysis, the process of determining the amounts 

 of the elements present in a compound or mixture. 

 (3) Proximate analysis, an analysis for the purpose 

 of detecting and estimating the presence of certain 

 compounds in a mixture. (4) Ultimate analysis, the 

 determination of the elements in a compound. (5) 

 Organic analysis, the qualitative and quantitative 

 analysis of organic compounds, involving the deter- 

 mination of carbon, hydrogen, nitrogen, sulphur, and 

 the halogens (iodine, chlorine, bromine, and fluorine). 



(6) Combustion analysis, a method of analysis of or- 

 ganic compounds for the determination of carbon, 

 hydrogen (and oxygen by difference), and nitrogen. 



(7) Electroanalysis. This method employs the electric 

 current to effect the separation of the constituents 

 of a compound or mixture. (8) Spectrum analysis, 

 the detection of elements by means of their char- 

 acteristic spectra. 



Atigstrom Unit. A unit for measuring the wave- 

 lengths of light. It is equal to one ten-thousandth 

 of a micron. See Millimicron. 



Aphelion, The point in an orbit (as of a planet) 

 farthest from the sun Qielios). By extension, in the 

 theory of the planetary atom, the point in the orbit 

 of an orbital electron that is farthest from the nucleus 

 of the atom. Opposed to perihelion. 



Archeozoic Era. The oldest era of geological his- 

 tory. The era of the earliest life-forms. 



Atmospheric Pressure. See Pressure, Atmospheric. 



Atomic Weight. The weight of an atom of a chemi- 

 cal element as compared with the weight of an atom 

 of hydrogen. The value 1 was arbitrarily assigned 

 to the weight of the hydrogen atom because hydro- 

 gen is the lightest of all the elements. On the basis 

 of hydrogen equals atomic weight 1, oxygen — found 

 to be sixteen times heavier than hydrogen — equals 



