94 EXPERIMENT STATION. [Jan. 



The insoluble fatty acids, or Ilelmer number, were deter- 

 mined by saponifying in a flask a definite amount of fat with a 

 glycerol-soda solution, destroying the resulting soap with dilute 

 hydrochloric acid, solidifying the insoluble fatty acids in ice 

 water, and filtering ; the acids, after repeated washing, solidify- 

 ing and filtering, were eventually weighed in the flask. It is, 

 of course, understood that all details and precautions were fully 

 observed. 



In the first period Herd 11. showed a slightly higher per- 

 centage than did Herd I. ; the same condition was observed in 

 the second period. In the third period this difference was 

 increased, due in a measure to the effect of the soy bean oil 

 in increasing the unsaturated acids. 



The saponification number of the insoluble acids was ob- 

 tained by titrating the weighed acids, dissolved in alcohol with 

 N/ 2 alkali solution; the number of milligrams of potassium 

 hydrate required to neutralize 1 gram of fatty acids is the 

 saponification number. But very little difference was noted 

 until the third period, when in case of Herd 11. a noticeable 

 depression was observed. 



The mean molecular weight (M) of the insoluble acids was 

 calculated from the saponification number (S) by the formula 



The soluble fatty acids represent the difference between the 

 total and insoluble acids. The fat produced by Herd I. (first 

 ])eriod) had rather more than did that yielded by Herd 11. 

 (also indicated by the Reichert-Meissl number). In the second 

 period the fat from Herd I. contained about the same per- 

 centage, the amount being reduced in the third period by one- 

 half per cent., due, probably, to the advance in the lactation 

 period. Herd II. in the second period showed a slight decrease, 

 from 8.13 per cent, in the first period to 7.75 per cent., and 

 in the third period the percentage had fallen to 6.13. 



The saponification of the soluble acids was calculated as 

 follows: knowing the saponification number of the fat, the 

 percentage and saponification number of the insoluble acids, 

 and the percentage of soluble acids : — 



