In the gravimetric determination of the fat (butter), 10 grammes of the milk are put into a tared platinum dish, containing a weighed amount of dry sand. The milk is evaporated as previously directed, the mixture being constantly stirred with a small platinum spatula. The residue is repeatedly treated with warm ether or petroleum naphtha of 70° B., and the solutions poured upon a small filter. The several filtrates are collected in a tared beaker, and cautiously evaporated, until constant weight is obtained. This will give the amount of _fat_. The undissolved residue remaining in the platinum capsule, or the difference between the quantity of fat and that of the total milk-solids, affords the proportion of _milk solids not fat_ contained, which, in unadulterated milk, should amount to 9 per cent. It has been determined by experiment, that every percentage of milk-solids not fat, increases the specific gravity of milk 0·00375, whereas each percentage of fat decreases the gravity 0·0010, and the proportion of solids not fat can be calculated from the data afforded by the lactometer and Feser’s lactoscope by means of the formula:-- (S - A) / 0·00375, where S is the specific gravity of the milk, as shown by the lactometer, and A is the remainder obtained upon multiplying the percentage of fat indicated by the lactoscope by 0·001 and subtracting the residue from 1·0000. The residue remaining after the extraction of the fat is treated with warm water containing a few drops of acetic acid, or with dilute (80 per cent.) alcohol, in order to remove the sugar. The residue is dried until it ceases to decrease in weight, and is then weighed. The difference between the original weight of the sand and the weight of the sand and residue combined represents approximately the amount of _caseine_ (albuminoids) present. As this contains a certain proportion of ash it is to be subsequently ignited, and the ash obtained deducted from the first weight. The alcoholic sugar solution is evaporated to dryness and weighed. The residue is then incinerated and the weight of ash is subtracted. The difference is the amount of _milk sugar_ contained. The sugar may likewise be determined by means of Fehling’s solution (see pp. 37, 111). About 50 c.c. of the milk is warmed with a small quantity of acetic acid to precipitate the caseine, which is removed by filtration, and the filtrate diluted to 500 c.c.; the test is then applied. 10 c.c. of the copper solution represents 0·067 gramme of milk sugar.