FATS AND FIXED OILS 



47 



difficult to identify any given sample of fat of unknown origin. 

 When several are mixed together it is usually impossible to 

 determine with certainty which of the various natural fats 

 have been introduced, or in what proportions they are present. 

 If, however, the properties of the mixture are known, it is not, 

 as a rule, very difficult to concoct another to match the sample 

 in all essential particulars. 



Qualitative Tests. The more important properties upon 

 which chemists are accustomed to rely for 

 these purposes are the colour, taste, smell, 

 viscosity, specific gravity, melting point, 

 amount of alkali required for saponification, 

 the iodine number, the rise of temperature 

 on treatment with sulphuric acid, the action 

 of nitrous acid and of chloride of sulphur, 

 and certain colour reactions with sulphuric 

 acid, nitric acid, etc. 



Quantitative Determination. The 

 methods employed for the quantitative de- 

 termination of fat in vegetable products 

 all depend, ultimately, on the complete ex- 

 traction of the fat from the sample by means 

 of solvents. Common ether or the so-called 

 petroleum ether (a mixture of the lighter 

 paraffins) is generally used. The Soxhlet 

 extraction tube is perhaps the most con- 

 venient form of apparatus for this purpose. 

 Many different modifications have been in- 

 troduced from time to time, but the original, 

 shown in the illustration (Fig. 6), has never 

 been superseded. The extracted fat may FIG. 6. Soxhlet's 

 either be weighed directly, after evaporating apparatus. 

 off the ether, or it may be deduced from the loss found by. 

 weighing the residue after drying. 



The result obtained by this process does not represent 

 pure fat ; it includes chlorophyll, waxes, and other substances 

 soluble in ether. It is called " crude fat " or " ether extract." 



