ANALYSIS OP BUTTER-FAT. 69 



Yet Dr. Muter's results unquestionably prove the correct- 

 ness of the conclusion at which we originally arrived by 

 slender evidence, namely, that butter contains a very notable 

 quantity of soluble acids. 



Lastly, we have, by adopting a different method, come to 

 the same result. The liquid which is obtained after the 

 insoluble fatty acids have been carefully washed, as in Dr. 

 Dupre's or Muter's process, is rendered alkaline and concen- 

 trated by evaporation. It is then made up to a known bulk, 

 which may be small, say 250 c.c. In one portion of this 

 liquid the amount of alkalinity is determined by means of 

 decinormal sulphuric acid. The rest of the liquid is 

 evaporated and incinerated. Thus the butyrate is converted 

 into carbonate of potash, the sulphate being not, of course, 

 altered. The alkalinity after incineration, diminished by the 

 alkalinity before incineration, indicates the proportion of 

 organic acids present. It must be remarked that the liquid, 

 before being evaporated, must be rendered distinctly alkaline, 

 as from a neutral liquid notable quantities of butyric acid 

 are volatilised; This method is simple and satisfactorily 

 accurate. 



Not so, however, we found a method which has lately 

 been recommended for the determination of mineral acids in 

 vinegar, and which is based upon the action of mineral acids 

 on methylaniline violet. This colouring matter was said 

 to be turned green by mineral acids, but to remain un- 

 changed by organic acids. Thus it would merely have been 

 necessary to determine the total acidity, litmus being used 

 as an indicator, and second, to use methylaniline violet, the 

 difference in the two determinations being calculated as organic, 

 in the case of butter, butyric acid. The colouring matter 

 alluded to does indeed turn green by the addition of mineral 

 acids, but it is so little sensitive, that comparatively large 

 quantities of acid are required to produce any visible change. 



