ONE HUNDRED YEARS OF CHEMISTRY 327 



method of determining the heats of formation of oxides 

 by combustion with sodium peroxide. By this same 

 method as well as by direct combustion in oxygen, he has 

 obtained results which appear to equal or excel in accu- 

 racy any which have ever been obtained in his field of 

 work. Richards 's work has consisted largely of improve- 

 ments in apparatus. He developed the so-called adia- 

 batic calorimeter which practically eliminates one of the 

 chief errors in thermal work caused by the heating or 

 cooling effect of the surroundings. This modification is 

 being generally adopted where extremely accurate work 

 is required. 



Organic Chemistry. 



One hundred years ago qualitative tests for a few 

 organic compounds were known, the elements usually 

 occurring in them were recognized, and some of them had 

 been analyzed quantitatively, but organic chemistry was 

 far less advanced than inorganic, and almost the whole of 

 its enormous development has taken place during our 

 period. 



Berzelius made a great advance in the subject by estab- 

 lishing the fact, which had been doubted previously, that 

 the elements in organic compounds are combined in con- 

 stant, definite proportions. In 1823 Liebig brought to 

 light the exceedingly important fact of isomerism by 

 showing that silver fulminate had the same percen- 

 tage composition as silver cyanate, a compound of very 

 different properties. Isomeric compounds with identical 

 molecular weight as well as the same composition have 

 since been found in very many cases, and they have 

 played a most important part in determining the 

 arrangements of atoms in molecules. They have been 

 found to be very numerous in many cases. For instance, 

 three pentanes with the formula C 5 H 12 are known, all 

 that are possible according to theory, and in each case 

 the structure of the molecule has been established. On 

 theoretical grounds it has been calculated that 802 

 isomeric compounds with the formula C 13 H 28 are possi- 

 ble, while with more complex formulas the numbers of 

 isomers may be very much greater. 



