v DECOMPOSITION PRODUCTS 225 



Two of them suffice, for whilst one is catching the distillate 

 the contents of the other can be titrated. 



The rate of distillation must be regulated Duclaux advises 

 40-45 minutes and when the distillation is over the relation 

 between the total quantity of lime-water used and the quantity 

 required for 10,20, 30, 40c.c.&c.,of the distillate is calculated from 

 the successive readings on the burette. The series of numbers 

 obtained in this way are compared with Table X in the Appendix, 

 and this shows the mutual relation between the acids present 

 in the mixture. The respective quantities are then calculated 

 according to the method previously described. 



Duclaux's method gives exact results when one, or at most 

 two, acids are concerned. If only one acid is present, it can be 

 estimated qualitatively or quantitatively by this method, but 

 when the mixture of two acids has to be dealt with, Jensen's 

 qualitative test must first be used, and the quantitative 

 investigation performed according to Duclaux. 



Often, however, several acids are present, and, if so, the 

 fractions must be so divided that only two acids are present. 

 Orla Jensen divides these fractions so that the precipitation of 

 the barium salts can be made fractionally with normal sulphuric 

 acid as already described. After each precipitation the barium 

 sulphate is filtered off and washed, and the free acid distilled 

 according to Duclaux's method. In this way the higher fatty 

 acids are obtained in the first fraction, and the lower ones the 

 last. The number of fractions depends upon the number and 

 properties of the acids present. No generally applicable rule 

 can be given, and in each case the procedure must be based 

 upon the results of the qualitative examination. Acids which 

 are only slightly soluble caproic,and still more caprylic cannot 

 be determined with exactitude by Duclaux's method. 



Further, as Orla Jensen x has proved it is not, as regards the 

 proportional number, a matter of indifference whether the acids 

 are normal or isomerides, for when acids of the same molecular 

 weight are present in aqueous solution, those which have the 

 lowest boiling point, that is the " iso " acids, distil over first, 

 and consequently higher numbers are obtained than for the 



1 "Contribution a la connaissance et a 1'analyse des acides gras volatils 

 dans les huiles de palme et de beurre," Landivirtschaftliches Jahrbuch der 

 Schweiz, 1905. 



Q 



