26G METHOD OF SEPARATING FATTY ACIDS. [BOOK I. 



the fats are to be extracted. PCbc is a glass connecter wlrich communi- 

 cates with an inverted Liebig's condenser, with a stopper which fits into 

 the upper part of , and with the tube a which is joined to the side of A. 

 When the flask A containing ether is placed upon the water-bath, that 

 liquid boils and the vapour passes through a and b to bPC ; it ascends 

 into the Liebig's condenser where it is condensed, and it then flows 

 back into B over the matter placed upon the plaited filter, and thence 

 into A. A continual circulation of ether is thus kept up, and the 

 dissolved fats accumulate in A. 



The ethereal solution is then evaporated to dryness in a weighed capsule, 

 and the weight ascertained. 



Separation ^e n^ture of neutral fats is dissolved in boiling alcohol 



of the fatty and the solution is poured into a silver basin, and then 



acids contain- treated with an alcoholic solution of caustic potash. The 



edintheneu- fl u ^ j s boiled for some time over a water-bath and then 



evaporated to dryness. Water is then added to the 

 residue so as to dissolve the soaps which have been formed, the solution 

 is now acidified by the addition of hydrochloric acid, then boiled 

 and allowed to cool. The fatty acids, which have been liberated from 

 the neutral fats, set in the form of an insoluble mass, which is collected 

 on a filter. This is then dissolved in hot alcohol and treated with an 

 alcoholic solution of lead acetate which precipitates all the fatty acids 

 in the form of insoluble lead salts. The precipitate is collected on a filter 

 and dried, and subjected to the action of boiling ether, which dissolves 

 only lead oleate, leaving lead stearate and palmitate. The ethereal 

 solution of lead oleate may be agitated with dilute hydrochloric acid, 

 which will decompose the salt, and the ether will then hold oleic acid 

 in solution which will remain on evaporation ; the treatment with HC1 

 should be carried out in an atmosphere of CO 2 . The mixture of lead 

 stearate and palmitate is heated with hydrochloric acid and thereafter 

 shaken with ether; the ethereal liquid is freed from acid by shaking 

 with water and the ether is then distilled off, when a mixture of palmitic 

 and stearic acids is obtained. 



The melting-point of the mixture is then taken. In order to do 

 this a very thin glass tube is made and a small quantity of the 

 mixed acids is dropped in ; the tube is then drawn out slightly. The 

 glass tube is now attached by means of a little india-rubber band (which 

 may be made by cutting a thin circular slice from the end of a narrow 

 india-rubber tube) to a finely graduated thermometer, in such a manner 

 that the part of the tube in which the fat lies is on the same level as the 

 bulb of the thermometer. The latter is then plunged into a beaker 

 containing water, which is immersed into a larger beaker also containing 

 water. (See the arrangement employed for determining the temperature 

 at which solutions of the proteids coagulate at p. 15). The latter is then 

 heated so that the temperature of the water in the inner beaker rises 

 very gradually. The observer watches very carefully the temperature 

 at which the fat nielts; he then withdraws the heat from the outer 

 beaker and, as the temperature of the water surrounding the thermo- 

 meter bulb falls, he notices the temperature of solidification of the 

 previously melted fats. 



