Dr. Stenhouse, of Liverpool, once made a careful analysis of a sample package of black tea, which was found to contain “some pure Congo tea leaves, also siftings of Pekoe and inferior kinds, weighing together twenty-seven per cent of the whole.  The remaining seventy-three per cent was composed of the following substances; Iron, plumbago, chalk, China-clay, sand, Prussian-blue, tumeric, indigo, starch, gypsum, catechu, gum, the leaves of the camelia, sarangna, Chlorantes officinalis, elm, oak, willow, poplar, elder, beach, hawthorn, and sloe.”

MILK CREAM BUTTER

MILK.

Chemically considered, the constituents of milk are nitrogenous matter (consisting of casein and a small proportion of albumen), fat, sugar of milk, mineral matter, and water, the last constituting from sixty-five to ninety per cent of the whole.

The proportion of these elements varies greatly in the milk of different animals of the same species and of the same animals at different times, so that it is not possible to give an exact analysis.

The analysis of an average specimen of cow’s milk, according to Letheby, is:—­

Nitrogenous matter.......................................4.1
Fat......................................................3.9

Sugar of milk............................................5.2
Mineral matter...........................................0.8
Water...................................................86.0

If a drop of milk be examined with a microscope, it will be seen as a clear liquid, holding in suspension a large number of minute globules, which give the milk its opacity or white color.  These microscopic globules are composed of fatty matter, each surrounded by an envelope of casein, the principal nitrogenous element found in milk.  They are lighter than the surrounding liquid, and when the milk remains at rest, they gradually rise to the top and form cream.  Casein, unlike albumen, is not coagulated by heat; hence when milk is cooked, it undergoes no noticeable change, save the coagulation of the very small amount of albumen it contains, which, as it solidifies, rises to the top, carrying with it a small portion of the sugar and saline matter and some of the fat globules, forming a skin-like scum upon the surface.  Casein, although not coagulable by heat, is coagulated by the introduction into the milk of acids or extract of rennet.  The curd of cheese is coagulated casein.  When milk is allowed to stand for some time exposed to warmth and air, a spontaneous coagulation occurs, caused by fermentative changes in the sugar of milk, by which it is converted into lactic acid through the action of germs.

Milk is sometimes adulterated by water, the removal of more or less of the cream, or the addition of some foreign substance to increase its density.

The quality of milk is more or less influenced by the food upon which the animal is fed.  Watery milk may be produced by feeding a cow upon sloppy food.