RkilI.y and HicictNBoTTOM — Volatile Fatty Acids. 537 



It will be noticed in Tables 10 to 14 that in practically all cases there is an 

 approximately constant difference between the theoretical and the recorded 

 figure. Whether this is due to unavoidable experimental errors or to the 

 acids present affecting each other is not certain. Eichmond recorded' a 

 similar observation. The deviation, however, is not much larger than the 

 experimental error, and does not affect the analysis of mixtures to any 

 appreciable extent. Provided that the modifications previously indicated are 

 adopted, the identity and purity of a solution of a single volatile fatty acid 

 can be readily established in most cases. Also, in the case of mixtures 

 it is i possible to quickly determine with a fair degree of accuracy the pro- 

 portions in which the acids are present. The conversion of the acids, in a 

 known volume of solution, into the corresponding barium salts, and 

 estimating the barium in the, dried separated compounds, is often a useful 

 confirmatory test. 



When the method of calculation used in the case of " two-acid " mixtures 

 is extended so as to include the analysis of mixtures of three acids, the 

 agreement between the calculated and the actual results is generally not 

 so close. This may be^ accounted for by the larger experimental error 

 involved. Furthermore, if in the case of two acids there is a disturbing 

 influence, it will be greater in the case of three acids. When dealing 

 with more than two acids, a. partial, fractionation first is sometimes advisable. 

 The separated fractions are analysed,,, and from the data , obtained , the 

 composition of the original, mixture is calculated.,, 



In addition to employing the distillation method for the estimation of 

 mixtures, in which the components are present in relatively large propor- 

 tions, it may also be employed to determine the purity of commercial pro- 

 ducts. It has been found that with commercially pure substances the fall in 

 the distilling constants is small, but. when appreciable amounts of impurities 

 are present the fall is very marked. .... 



When dealing with fermentation or other liquids containing non-volatile 

 or slightly volatile acids, we have found it advisable to distil off the volatile 

 acids. under reduced pressure, and then to estimate them in the condensed 

 liquids by the ordinary distillation method. 



A knowledge of the behaviour of . the higher volatile fatty acids on 

 distillation is desirable on account of. their occurrence in many commercial 

 oils and fats. By suitably adapting the apparatus described in this paper 

 the distillation constants for the volatile acids contained in butter and 

 coco-butter can be determined. Utilizing these constants the presence of . 

 adulteration may be detected. It is observed that these distillation con- 

 stants change when a variation is made in the relative proportion in which 



SCIENT. PROC. E.D.S., VOL. XV., NO. XXXVII. . . 4 O . ,. 



