448 Conditions Affecting Butter-Fat. 



has been accumulated concurrently with the rise and develop- 

 ment of the margarine industry, and largely in consequence 

 of it. 



The fat of margarine mainly consists of glycerides of stearic, 

 palmitic, myristic, &c, acids, and is distinguished from the fat 

 of butter by the absence or practical absence of acids of 

 relatively low molecular weight. 



The amount of iodine absorbed, calculated as a percentage on 

 the fat, is generally referred to as the " iodine number" or the 

 " Hiibl number " of the fat. 



Other points of contrast depending upon differences in the 

 chemical composition of the two fats are found in their different 

 deportment with certain solvents. Thus, if equal weights of 

 butter-fat and margarine-fat be separately dissolved in similar 

 volumes of hot acetic acid, and then allowed to cool, the 

 glycerides of margarine begin to crystallise out, and render the 

 liquid turbid, at a considerably higher temperature than do 

 those of butter. This test with acetic acid is known as the 

 " Valenta" test, after its discoverer. A somewhat similar 

 experiment, in which alcohol is used as the solvent, is known as 

 " Crismer's test" and the temperature of turbidity as the 

 " Crismer number? Moreover, different quantities of heat are 

 evolved by the two fats when, under like conditions, their 

 glycerides are chemically decomposed by treatment with strong 

 sulphuric acid. 



These differences in the chemical composition of butter-fat and 

 margarine are accompanied by certain differences in physical 

 properties of which advantage may be taken by the analyst. 

 Thus butter-fat has almost invariably a higher relative density 

 than any of the fats which are likely to be used to adulterate it. 

 Its refractive index also is lower than that of any probable 

 adulterants. This latter constant, as measured by the optical 

 instrument most generally used, is known as the " Zeiss number? 

 As a rule, the lower the proportion of volatile acids in butter-fat, 

 the higher is the Zeiss number. Its value for normal butter-fat 

 at 45 deg. C. ranges from about 38 to 43 divisions on the gradu- 

 ated scale attached to the instrument. 



Founded upon the foregoing facts, various analytical processes 

 have been devised in order to ^discriminate between butter and 



