The analysis and adulteration of foods / by James Bell.

  • Bell, James, 1824-1908.
Date:
1881-1883
Catalogue details

Licence: Public Domain Mark

Credit: The analysis and adulteration of foods / by James Bell. Source: Wellcome Collection.

    45/210 (page 33)
    the effect of the above treatment with sulphuric acid will be to reduce the total rotatory power of the sugars in the milk, and by calculation the difference in the degree of inversion can be made to show very nearly the proportion of cane-sugar added. The polariscope test is applied in the manner described on page 13. The estimation of cane-sugar in milk may also be effected by the copper test, by ascertaining the percentage of sugar before and after inversion by sulphuric acid. When milk is boiled for four minutes with 5 cubic centimetres of normal sulphuric acid, the increase of sugar over the quantity found before inversion is only equal to about two-tenths per cent., but when cane-sugar is present the indications will equal the cane-sugar in the milk, together with the two-tenths per cent, derived from the altered milk-sugar. Glycerin.—This, when present, may be identified by evaporat- ing the whey, or serum, after coagulation of the casein by rennet or dilute acids, and removing all traces of the fat by dry ether. The milk residue is then treated with a mixture of ether and alcohol, which will dissolve out most of the glycerin. After the evaporation of the solvent the glycerin, if present, will be found as a permanently sirupy residue, which can be identified by the application of the usual tests. CREAM. Cream consists chiefly of the fat of milk, but it contains also variable proportions of water, milk-sugar, and casein. The sugar bears nearly the same relation to the water as that in the milk, but in cream obtained by skimming the proportion of casein, or curdy matter, is in excess compared with the water present. This is explained by the presence of an adherent pellicle, or D