Reilly and Hickinbottom — Volatile Fatty Acids. 527 



iso-Butyric Acid. Sodium isobutyrate, from Kahlbaum, was purified by 

 two crystallisations from absolute alcohol and the free acid obtained by 

 distillation with glacial phosphoric acid. The distillate after partly drying 

 with a small amount of phosphorous pentoxide was fractionated twice, the 

 acid being collected over a range of 0-2° C, boiling-point, 155-3-155-5 

 (uncorr.). 



n- Valeric Acid, from Kahlbaum, was fractionally distilled twice, using a 

 rod and disc column, the fraction collected between 183-2-183-5 (uncorr.) 

 being reserved for a determination of the constants. 



iso-Caproic Acid (isobutylacetic acid). A specimen of Kahlbaum's iso- 

 caproic acid was distilled twice through a rod and disc column, the fraction 

 collected between 199'7-200° 0. (uncorr,) being used. 



For the acids higher than butyric similar tables to these given for the 

 lower fatty acids have been worked out. These data are not given in full 

 here, but Table 8 gives a summary of results obtained. 



Table 8. 



Examining Tables 4-7 it will be seen that although there is only a small 

 change in the constants for the lower members of the series, there is a more 

 decided fall with some of the higher members. It is probable that this 

 cannot be due to change of constant with concentration, as the constants of 

 fatty acids other than acetic and formic acids are not altered to any 

 appreciable extent by change of concentration. 1 It is possible, therefore, 

 that the fall in the. constants may be brought about by traces of impurities 

 which are very difficult to remove completely from the higher members. 

 Also it should be noted that with the higher fatty acids the difficulty of 

 accurately determining the constants increases with the fall in solubility of 

 the acids. 



Compare Richmond, loc. cit- 



