Per cent. Sodium chloride 10.62 Potassium chloride 9.16 Monopotassium phosphate 12.77 Dipotassium phosphates 9.22 Potassium citrate 5.47 Dimagnesium citrate 3.71 Magnesium citrate 4.05 Dicalcium phosphate 7.42 Tricalcium phosphates 8.90 Calcium citrate 23.55 Calcium oxide, in combination with casein 5.13 ──── 100.00 ────── The presence of citrates will be noted in this analysis. Citric acid, which gives to lemons their acidity, and is also found in other fruits, has been proved to exist in milk to the extent of about 0.2 per cent. When alkaline or earthy citrates are burnt or oxidised in the blood, the citric acid is destroyed, and corresponding carbonates remain. No doubt the function of citrates in milk is to furnish to the body the earthy and alkaline carbonates which are required in certain of its parts. The mineral constituents of milk have many important functions to perform in the building up and nutrition of the bodily organism. Phosphate of lime is the principal constituent of the skeleton, and the blood must be richly supplied with the alkalies, earths, and acids which are comprehended in the ash. Milk contains traces of many other substances, the most important of which are several enzymes which assist in its digestion. _General Properties of Milk._—The appearance of milk is known to every one; it ought to be a pure white opaque liquid, but very generally it is tinted a cream colour with anatto to give it an added appearance of richness. The average specific gravity is about 1.031; or, to put it another way, while a gallon of pure water weighs exactly 10 lbs., a gallon of milk weighs 10 lbs. 5 oz. It freezes at 31° F. and boils at about one third of a degree higher than water. When milk is examined under the microscope, the fat is found to be distributed through it in a multitude of minute globules varying in size from 1/16,000th to 1/25,000th part of an inch, and occasionally they are much smaller and also much larger. Fig. 1 is a micro-photograph showing the fat globules in whole milk. Fig. 2 is a micro-photograph of separated milk, and Fig. 3 a micro-photograph of cream, all under high magnification (450 diams.); from these figures the comparative number of fat globules present may be seen. [Illustration: FIG. 1.—Micro-photograph of a Drop of Whole Milk, showing distribution of fat globules. (Magnified 450 diams.)]