90 EXPERIMENT STATION. [Jan. 



may be calculated from the ether number.^ The above results 

 were secured by the latter method on the understanding that 

 3 molecules of potassium hydrate replace 1 molecule of 



g ycero . — 168.474 : 92.064 : : 1 : G. 



in which case G = .5465. 



Multiplying the ether number, therefore, by .05465 gives the 

 percentage of glycerol. Direct determinations of glycerol in 

 neutral fats by quantitative methods, and by the above method 

 of calculation, have given substantially identical results. Thus, 

 Brown found in beef tallow 10.61 per cent, by determination 

 and 10.68 by calculation, and in butter fat 12.70 and 12.69 

 per cent, respectively.- Bell has found 12.54 per cent, of 

 glycerol in genuine butter fat.^ Our own results compared very 

 closely to the above figures, excepting in the case of Herd II. 

 in the third period, when the average falls to 12,04 per cent. 

 This is in harmony with results already presented, and indicates 

 a decrease in the amount of the soluble acids of high combining 

 power and low molecular weight and a corresponding increase 

 in the insoluble fats. 



The percentage of total fatty acids was calculated in accord- 

 ance with the formula presented by Zulkowsky.'* This method, 

 in common with that for the determination of the glycerol, de- 

 pends upon the determination of the ether number. The for- 

 mula is as follows : — 



C3H,(ROo)3 + 3 H,0 = C3H5(OH)3 + 3 ROoH 



Fat + water (54.048) = glycerol (92.064) + fatty acids. 



r^ .. -A inn , 54.048 ^ ^ ^_. 38.016 „ 



Fatty acids = 100 + ^^-^ G — G; or 100 — ^^-^ G. 



Substituting the value of glycerol in terms of ether number : — 



3S 01 6 

 F = 100— ^^•^'" X .05465 E or 100— .02257 E. 

 92 . 064 



The total fatty acids as presented in the tables are all quite 

 uniform, excepting for Herd II, in the last period, when they 

 increased slightly, for the reason already mentioned. 



1 Lewkowitsch, third edition, Vol. I., p. 281; original by Ziilkowsky, Berichte, 16, p. 1140. 



2 Loco citato, p. ilO. < Herichtc, Ifi, p. 1315. 



3 Licwkowitscli, p. 833. 



