the Relative Affinities of certain Acids. 



561 



It also showed that the comparative affinity of nitric acid has 

 hitherto been placed somewhat too high. Taking hydrochloric 

 acid as 100, nitric acid scarcely exceeds 75. 



The weaker acids, being for the most part without action 

 on the test solution, give satisfactory results. Oxalic and 

 tartaric acids must, however, be excepted, the acid set free 

 tends to form acid salts of sparing solubility, these are pre- 

 cipitated: thus the conditions are changed. 



The results obtained are here tabulated : — 



Succinic. 



29-37 

 1-21 

 2-28 

 102 

 0963 

 1-2 



13-68 

 0-21 

 0-14 

 0-53 

 0-926 

 0-2 



100 

 1-54 

 1-02 



3-87 

 6-77 

 1-46 



Acetic . . 



Citric 



Py rophosph oric 



v JT IT 



Tungstic 





The first column of this table shows the absolute number 

 of molecules of the sodium salt which must be added without 

 regard to the basicity of its acid, in order that one molecule of 

 sulphuric acid may be so completely saturated with base as 

 no longer to give a reaction for free sulphuric acid. 



In the second column these numbers are modified in such 

 manner as to cause them to justly represent the comparative 

 affinity of the acid. With monobasic acids the number of 

 molecules is divided by 2, with quadribasic acids it is multi- 

 plied by 2. For a tribasic acid it is multiplied by |-. Bibasic 

 acids only remain unchanged. Next, unity is subtracted 

 because it is always the excess of the salt which must be present 

 in order to keep the sulphuric acid saturated with base that 

 gives the measure of the affinity of the acid. Were this 

 correction not applied, the entire result would be vitiated. 



The third column gives the numbers as they appear when 

 hydrochloric acid is taken as 100. 



Instead of adding salts of different acids to sulphuric acid, 

 we may add various acids to a salt formed by the union of 

 sulphuric acid to a strong base, for example, to sodium 

 sulphate. 



Sulphuric acid is now recognized as being a weaker acid 

 than hydrochloric, and yet we have seen that it is able to 

 detach a certain quantity of base from a chloride. Further, 



