INTRODUCTION. 25 



The elements in acetic acid hence stand to each other 

 in the atomic proportion of 3.33 : 6.67 : 3.33, or, 1 : 2 : 1. 

 The chemical formula of the acid could hence be ex- 

 pressed by CH 2 0, but, of course, with exactly the same 

 right, we might express it by C 2 H 4 2 , or C 6 H 12 0, for 

 all these formulae show the same percentages of the 

 elements. Simply the elementary analysis is not suffi- 

 cient to determine which of these formulae is the cor- 

 rect one ; an estimation of the molecular weight must 

 be united with it. With an acid this is simple if we 

 know its basicity. We know that, for the purpose of 

 forming a neutral salt, one molecule of acetic acid 

 gives up one atom of hydrogen, and takes up in its 

 place one atom of a monovalent metal. Hence, in 

 order to find the molecular weight of acetic acid, we 

 need only determine the amount of metal contained in 

 one of its salts. 



0.412 grrn. silver acetate on being ignited leave a 

 residue of 0.2665 grm. metallic silver. This represents 

 64.7 per cent. 



In 100 parts of silver acetate are hence contained 



Organic substance .... 35.3 

 Silver 64.7 



The molecular weight of the organic substance in 

 silver acetate can now be found by means of the fol- 

 lowing proportion : 



64.7: 35.3 :: 10S*:x 



Eesult = 59 



Free acetic acid contains one atom more of hydro- 

 gen, therefore the molecular weight of the free acid 

 is 60. 



The simplest formula, agreeing with the results of 

 the analysis, has the molecular weight 30. This must 

 hence be doubled, and the composition must be expressed 

 by the formula C 2 ITO 2 . 



When basic bodies are under investigation, a neutral 



* Atomic weight of silver. 



