ARTIFICIAL THICKEXIXG OF CEEAII. 273 



Now let the standard viscosity be 25. 



log 25 = 1-39794, and log 1-39794 = 0-14550 

 therefore, 5-21463 = 0-14550 + 5-06913 



now 5-21463 = 3 X 1-73821 = 3 log 54-7, 



and the percentage of fat in cream reduced to standard viscosity is 52 per 

 cent, by weight, or 54-7 per cent, by volume. 

 Now a = 61 -4, and 6 = 52-0 



then 100 (^-^)= 19-4; 



that is, to each 100 parts of cream 19-4 parts of milk must be added to 

 reduce it to standard thickness. 



By the formula V = 1 0''^' the percentage of fat calculated in the cream 

 of standard viscosity is 51 '7, which is a figure sufficiently close for practical 

 purposes. 



Artificial Thickening of Cream. — Cream has been arti- 

 ficially thickened by the addition of various foreign substances ; 

 thus, gelatine, isinglass, 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 (approximately) of 

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

 nitrate solution (p. 90), 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. 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. 105) 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 02 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 



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