The proportion of casein is most easily determined by precipitation by alum at 40° C. (104° F.) and by the proportion of nitrogen in the filter residue. Dilute 10 c.e. of milk 4 to 6 times and keep it heated to 40° C. (104° F.); add 1 c.c. of concentrated alum solution of potassium, and then slowly add anew c.c. at a time until perfect coagulation ensues. With human milk add XaC1 during precipitation, and a little calcium phosphate before filtration.
The proportion of can be determined by polarization of milk which lies been freed from albumin by mercury nitrate; by finding the reducing power of milk which has been treated according to Ritthausen with and caustic soda; or by fermenting inverted milk by Lohn stein's method (5 c.c. milk and 0.4 c.e. 25 per cent. 1IC1 for 30 minutes in a bath of water saturated with salt, at 100° C. (212° F.). Cool and neutralize this by means of 1 c.c. liquor kalii caustiei and pour off 10 c.c. Ferment this in the fermentation saccharometer with compressed yeast, at from 32° C. to 3S° C. (90°-100° F.) for 2 to 3 hours. The reading multiplied by 4.33 will give approximately the amount of sugar in the milk.
The so/ids may be either determined directly or calculated from the specific gravity and the proportion of fat. (This has not been worked out for human milk.) The specific yrarity can lie determined with a good aerometer, at definite temperatures bet ween 10° C. and 20° C. (5-1.°-fiti° F.) by plung ing the clean instrument as far as the 30 mark into milk that has been thoroughly shaken, and then allowing it to float. The degrees (so the hundredths and thousandths are called; c.y., 3.25--I.0325) which are this obtained are to be corrected for 1.5° C. (60° F.) by adding 0.2 to the degrees of density for every degree of temperature over 15° C. (60° F.) and substratiting a like amount for every degree below. There are correction tables for this purpose. On the Soxhlet lactometer the ther mometer shows the correction automatically. According to Fleischman]) when s denotes the specific. gravity; r (solids exclusive of fat) is to be reckoned as t—f. There are tables for reckoning both amounts, anti also the calculating machines of Ackermann (Switzerland) and Rich mond (England).
When milk is skimmed, f and t and s and r increase.
When water is added all decrease, but if at the same time the milk is skimmed, s may remain unchanged. Watering may also he detected by the lowering of the index of refraction and of the specific gravity of the whey (with rennet whey the normal is 1.027 1.030; with acid
whey-20 c.c. acetic acid to 500 c.c. milk heated to 60° C. (140° F.) in closed bottles and filtered—the normal is 1.0257-1.029), by the viscosity, by the electrical conductivity, by the lowering of the freezing point of the milk (over-0.55° C'.). If water emitaining nitrates is used, the nitrate reactions will furnish valuable data (diphenylamine, sul phuric acid, and HUI or NaCl with the whey; formalin and Addition of alkalies may be detected by testing the milk and an equal quantity of 96 per cent. alcohol, by means of a few drops of 1 per cent. rosalic acid, producing a rosy red. It will turn brown when boiled.
Boracic Acid.—The ash when dissolved in IIC'l, filtered, and neu tralized, becomes cherry colored with turmeric. When moistened with and decomposed by methyl alcohol, it is distilled and the vapors burn with a green color.
Salicylic acid.—A solution in ether, evaporated and dissolved in alcohol, turns violet with ferric chloride.
Formalin.—The distillate gives a dark color when tested with am moniacal solution of nitrate of silver and liquid ammonia in a (lark place. A red color is obtained by boiling with resorcin and 5() per cent. NaOH. A red violet is obtained from 5 c.c. of milk. 2 drops of diluted and 1 c.c. of solution of fuchsin which is just discolored by sulphate of sodium. Adding a small amount of amidophenol to the whey gives a yellow color. Morphine sulphate dissolved in gives a blue ring, and there are many other reactions.
Healing above 70° C. (158° F.) can be detected by the absence of the peroxide reactions (adding guaiacol to milk and then stirring in 1 per cent. peroxide a drop at a time; fresh unheated milk turns red). Less convenient are the reactions of Starch (10 c.c. milk, 1 drop 2 per cent. 2 drops 2 per cent. paraphenyldiamine solution; gives a blue color), and those caused by a layer of tincture of guaiacum, which gives blue. When the casein has been removed by filtration (saturation with or filtration by the clay cell), the filtrate, when heated to a high temperature, will give on boiling no coagulation that will not disappear with a little acetic acid.
If the physician wishes to have the compounds of the milk tested by an expert, the sample may be preserved by adding 20 drops of forma lin or Gm. of trichromate of potassium to the litre.