426 CREAM. 



Artificial Thickening of Cream. Cream has been arti- 

 ficially thickened by the addition of various foreign substances ; 

 thus, gelatine, isinglass, agar-agar, and substances of like nature 

 have been employed, but without great success, as the cream thus 

 treated has an appearance markedly different from that of 

 genuine cream. The following method, due to Stokes, may be 

 applied to detect gelatine in cream : To 10 grammes (approxi- 

 mately) of cream add 25 c.c. of water and 2 c.c. of Wiley's acid 

 mercuric nitrate solution (p. 155), and shake well ; filter through 

 a dry filter. In the presence of much gelatine the filtrate cannot 

 be obtained clear, and it is not essential that it should be so. On 

 adding a saturated aqueous solution of picric acid a yellow 

 precipitate is formed in the presence of gelatine ; if the quantity 

 of gelatine be but small, the precipitate does not form at once, 

 but the solution becomes turbid, and precipitates after a lapse 

 of some minutes. Seidenberg finds that sour cream gives a 

 precipitate with picric acid, which can be distinguished from 

 that given by gelatine by its insolubility in hot water ; the 

 hot water solution can be filtered, concentrated, and retested 

 with picric acid for gelatine. Starch, which has been gelatinised 

 by heating, has also been used ; this, of course, is readily detected 

 by the characteristic blue coloration given with tincture of 

 iodine. Of comparatively recent introduction is " viscogen," 

 which is a solution of lime in cane-sugar syrup ; the addition of 

 a small amount of this substance has a remarkable effect in 

 increasing the thickness of cream. It is sold under various 

 fancy names. 



Its presence may be detected by testing the cream by one of 

 the methods (p. 165) for the detection of cane sugar ; the amount 

 of ash will be raised, and the ratio of lime to phosphoric acid in 

 the ash will be higher than 17 : 23. It is usually added in quan- 

 tities of about 0-5 per cent., and this amount increases the solids 

 not fat by about O2 per cent, of cane sugar, the ash by about 

 0'04 per cent., and raises the ratio of lime to phosphoric acid to 

 about 1:1. 



As homogenised cream will not whip, it is not uncommon to 

 add gelatine, agar, or gum tragacanth for the purpose of making 

 a fairly permanent foam when the cream is whipped. Of these, 

 gum tragacanth added in the proportion of 0-1 per cent, is the 

 most effective. A careful microscopic examination of the cream 

 after the addition of a little iodine solution will reveal the presence 

 of particles of gum tragacanth, in which starch granules can be 

 detected. Agar, which has also been used as a thickening agent, 

 gives Cayaux's resorcinol test for cane sugar, but not any of the 

 other tests. 



