EXTRACTION OF FATS ii 



operation is most conveniently carried out in a Soxhlet 

 apparatus (see below). 



Previous tq extraction, the substance must be thoroughly 

 dried. For this purpose it must either be gently heated in a 

 current of dry air or else desiccated by means of alcohol or 

 anhydrous salts. 



The first method, which is the most convenient, should, 

 however, be used with caution, as many fats may undergo 

 chemical change during the process, as a result of which the 

 material extracted by ether after drying may be very different 

 from the substance originally present in the moist sample. 



The second method, which consists in treating the sample 

 to be dried with absolute alcohol for some hours and then 

 filtering and pressing, depends on the fact that the alcohol 

 withdraws the water without dissolving away any appreciable 

 quantity of the fat ; if treated two or three times in this way 

 the substance will be practically free from moisture and can 

 then be extracted under a Soxhlet with ether. The wet 

 alcoholic filtrates on careful evaporation yield a residue which 

 may be separately treated with ether to extract any fat con- 

 tained in them. It is unnecessary to remark that the method 

 cannot be employed if the fat to be extracted is soluble in 

 alcohol. 



The third method of drying, which involves the use of an- 

 hydrous salts such as sodium sulphate, depends on the fact 

 that the anhydrous salt when ground up with the moist tissue 

 withdraws the water from it, forming the hydrated crystals. 

 In a few hours the substance is sufficiently dry to be powdered. 

 The chief objection to this process is the fact that a considerable 

 bulk of salt has to be employed and consequently the volume 

 of the material to be extracted is much increased. 



PHYSICAL PROPERTIES OF FATS. 



The naturally occurring fats vary in consistency from oils 

 to wax-like solids ; the solid fats have mostly a low melting 

 point which is, however, rarely a sharp one, as natural fats 

 are not simple substances, but are, as a rule, mixtures of 

 several different chemical individuals ; such mixtures never 

 have sharp melting points. 



All fats and fatty oils are lighter than water, their specific 



