ANALYSIS OF BUTTER-FAT. 45 



Experiment 5. 10 grammes of the same butter as used in 

 4, yielded 4 '7 9 6 per cent. 



Experiment 6. 6*565 grammes of the same butter yielded 

 7-452 per cent. 



Experiment 7. 7 '346 grammes of the same butter gave 

 7-259 per cent. 



Experiments 4 to 7 having been made upon the same 

 sample of butter-fat, prove that constant results cannot be 

 obtained by means of distillation, the percentage of the 

 volatile acids varying from 4 -8 to 7 '4. 



Experiment 8.' Another genuine butter yielded 6*026 per 

 cent, of volatile acids. This distillation was carried on so far, 

 that the glycerin contained in the solution began to char 

 and to be converted into acrolein ; but the distillate was 

 still strongly acid, more so indeed than it had been at the 

 commencement of the experiment. 



From these determinations, imperfect as they are, it became 

 evident that from 6 to 7 per cent, of volatile acids may be 

 obtained from butter-fat merely by distillation, whilst at the. 

 same time it was sufficiently proved that constant results 

 cannot be obtained by following the method described, and 

 that either not the whole amount of the volatile acids c^n 

 thus be separated, or that the formation of products of decom- 

 position of the glycerin vitiates the result. The great 

 constancy of the melting point strongly indicated a corre- 

 sponding constancy of the chemical composition. Seeing 

 then, that the direct determination of the butyric acid could 

 not be done with anything like accuracy, we had recourse to 

 an indirect method of estimation. 



We have mentioned above, that all natural fats are mix- 

 tures of different tri-glycerides, and with the exception of 

 butter, the group of animal fats consists of tri-stearin, tri-pal- 

 mitin, and tri-olein. With the animal fats we are more imme- 

 diately concerned, as only these have ever been alleged to be 



