26 INTRODUCTION. 



salt is also prepared for the estimation of the molecular 

 weight, and from the quantity of acid contained in 

 this salt the molecular weight of the base is calculated 

 in a similar manner. 



The molecular weight cannot, however, in all cases 

 he determined by this method only when experiments 

 have shown how many atoms of a monovalent element 

 an acid, or how many molecules of a monobasic acid 

 a base, needs to form a neutral salt. If the substance 

 is volatile without decomposition, the molecular weight 

 can be found more simply by an estimation of the 

 specific gravity of its vapor. 



The specific gravity of acetic acid vapor, for instance, 

 was found to be 2.08 at 300. This number, multi- 

 plied by the constant number 28.9 (see ante, p. 14), 

 gives as a result for the molecular weight of acetic 

 acid the number 60.1, hence, taken together with the 

 results of the analysis, the formula C 2 H 4 2 . 



The processes, more intimately connected with the 

 formation of the primitive organic compounds in the 

 living organism of plants and animals, are almost 

 entirely unknown to us. We only know with cer- 

 tainty that all organic material is originally formed in 

 plants, that for this purpose plants make use of the 

 elements of existing compounds particularly of carbonic 

 acid, water, ammonia, and the inorganic acids of nitro- 

 gen, and that this process of formation takes place 

 only under the influence of sunlight and of certain 

 inorganic salts, which are absorbed from the soil ; the 

 manner in which this takes place is, however, up to 

 the present, inexplicable. The animal organism, on 

 the other hand, receives its constituents in the food in 

 the form of organic compounds already existing. 



A great many of the organic compounds occurring 

 in nature can be produced artificially from the elements, 

 but in by far the most cases the conditions and the 

 chemical processes are entirely different from those 

 through the instrumentality of which the formation 

 occurs in nature. 



