299 



removed; those which form afterwards are kept separately, and 

 only such portions the fusing- points of which are the same should 

 be united. Now crystallise the portions of the lowest fusing- 

 point in hot alcohol and proceed as before, i.e., evaporate the 

 mother-ley slowly and examine the crystals obtained each morning. 

 Recrystallise again the portions of the lowest fusing-point until 

 finally an acid is obtained which does not alter its fusing-point on 

 recrystallising. Compare the fusing-point of this second acid 

 likewise with those of the fat-acids known, and if found difierent 

 from any of them, ascume it to be a new acid and determine its 

 properties, chemical composition, and atomic weight. 



These operations require very much time and yield a satisfactory 

 result only with an adequate quantity of raw material. Some- 

 times the separation of the solid fat-acids is rendered quicker and 

 more effectual by converting them, as is done with the liquid fats, 

 into soda-soaps, and by precipitating the alcoholic solution with 

 acetate of magnesia, but in such a manner that (after the qxxantity 

 of the acetate of magnesia required for precipitating the whole of 

 the soap has been found previously by testing with a small sample 

 of the liquid) the precipitation is effected in at least three distinct 

 equal parts successively; the pi-ecipitate obtained from each portion 

 is then washed separately, decomposed with hydrochloric acid, 

 and the fat-acid thus separated is treated as already previously 

 explained. 



Sometimes mixtures occur of more than two fat-acids ; to 

 analyse which the quantity obtained fi-om 100 grammes of the 

 vegetable substance would prove inadequate, and therefore more 

 of the fat has to be obtained first, or the analysis in this respect 

 can not be proceeded with. 



(b) Distil the acid liquids, separated from the fat-acids, in a 

 retort furnished with a refrigerator and receiver, until about three- 

 quarters of the whole have passed over. It is the purpose of this 

 operation to find out if any volatile fat-acids soluble in water be 

 present (as formic, acetic, 2i')'0'pionic, butyric, valerianic, caproic, 

 caprylic, capric). If the distillate proves neutral, then no such 

 acid is present; should it show acid reaction, then mix it with some 

 carbonate of baryta previously triturated to an impalpable pulp with 

 a little of the distillate, and evaporate. Should, during the evapo- 

 ration, the used carbonate of baryta be completely dissolved, then 

 a new quantity ought to be added, for only an excess of it gives 

 the certainty that nothing of the volatile acids is lost. After the 

 liquid has been brought to a certain degree of concentration, and 

 when found of neutral reaction, it has to be filtered from the 

 excess of carbonate of baiyta. 



The carbonate of baryta remaining on the filter, after it has been 

 washed with warm water, may possibly contain a salt of a new 

 volatile fat-acid, which with baryta might form an insoluble com- 



