18 ORGANIC EVOLUTION CONSIDERED 



the above times would be reduced to about 7,700,000 

 and 47,500 years respectively. 



Assuming a specific number of molecules per cubic 

 centimetre of any gas, and accepting the hypothesis 

 of Avogadro that equal volumes of all gases under 

 like conditions of temperature and pressure contain 

 equal numbers of molecules, it becomes easy to calcu- 

 late the number of molecules of simple substances 

 that constitute any solid or liquid that can be readily 

 converted into the form of gases. 



For example, a cubic centimetre of nitric acid, the 

 formula of which is H NO3, specific gravity 1.517, 

 is composed of about 272 cubic centimetres of nitro- 

 gen, 273 of hydrogen, and 809 c. c. of oxygen, the vol- 

 ume of the three gases together is 1354 c. c. When 

 these three gases unite to form nitric acid the 1354 

 c. c, shrink to 1 c. c. Assuming 19,000,000,000,000,- 

 000,000 molecules in 1 c. c. of the gas, there would be 

 in 1354 c. c. 25,726,000,000,000,000,000,000 molecules, 

 which enter into the 1 c. c. of nitric acid. The cube 

 root of the above number is about 29,500,000, so that 

 according to this estimate if the molecules of nitric 

 acid fill the entire space in the 1 c. c, so that there 

 are no vacant spaces between the molecules, then a 

 molecule of the above gases is, on the average, about 

 V^'soo.ooo of a centimetre in diameter, which is about 

 Vraireojooo, of an inch. 



One cubic centimetre of water is composed of 1258 

 c. c. of hydrogen and 629 c. c. of oxygen — in all, 1887 

 cubic centimetres. Estimating, as in the case of nitric 

 acid, 19 quintillions of molecules in each cubic centi- 

 metre of gas at O C and the pressure of one atmos- 

 phere, there would be 35,853,000,000,000,000,000,000 

 molecules of the two gases in 1 c. c. of water, which 

 would allow an average diameter of about V^o^ooo 



