695 



the up|)er liniil (if the (irsi range of eoaoiilation (hydrochloric acid 

 and nitric acid — «iiiphuiic acid — acetic acid) is not the same as at the 

 lower limit of the second range of coagulation (sulphuric acid — nitric 

 acid — hydrochloric acid ^ acetic acid). 



^ 8. Injiuence of the acidity of the latex itself. 



As already stated in ^ i latex is feebly acid, and on being left 

 to itself gradually increases in acidity. The acidity of the latex, 

 which is used for the researches, is of course not without influence 

 on the figures obtained, though the relation need not be purely 

 additive, as the acidity in latex is caused by carbonic acid and 

 organic acids amongst which, after the action of bacteria, lactic acid, 

 acetic acid and butyric acid. 



First of all we made a few observations in ordinary latex and 

 in the same latex after neutralisation with hydroxide of potassium, 

 i.e. again for the limits, to be fixed sharply, of the first range of 

 coagulation in mixtures with little latex. A mixture with h';^ latex 

 (percentage of rubber 1.437o needed) for the neutralisation (plienoi- 

 plithalein as indicator) 16.6 cc. ' ,„ N hydroxide of potassium per 

 Liter, and therefore was 0.00166 normal; for the original latex we 

 calculate from tiiese data an acidity of 0.033 N. A mixture with 

 27o latex (percentage of rubber 0.547oJ required 6.6 cc. hydroxide 

 of pota-ssium and therefore was 0.00066 normal (i.e. also 0.033 N 

 calculated for original latex). 



The limits of the first range of coagulation appeared to be with 

 hydrociiloric acid : 



TABLE 6. 



Addition hydrochloric acid 

 in normality 



Lower limit 



Upper limit 



5 "/o latex, original 

 id. , neutralized 



2 u/o latex, original 

 id. , neutralized 



0. 00166 



0.0066 



We see, that the neutralization has increased the necessary addition 

 of acid with about the amount of the own acidity of the latex. In 

 judging the figures we should bear in mind that the neutralized 



