which should, however, be ignited until it shows a greyishwhite colour. The amount of ash in genuine milk ranges from 0.70 to 0.80 per cent. The addition of water naturally decreases this proportion as well as that of the total milk-solids.

c. Fat, Milk Solids not Fat, Caseine, and Milk Sugar.—An approximate estimation of the fat in milk was formerly made by the use of the creamometer. This instrument consists simply of a long glass tube, provided at its upper end with a scale. The milk under examination is introduced into the tube and allowed to remain at rest for about 24 hours, or until the stratum of cream has completely collected upon its surface; the quantity is then read off by means of the attached scale. The results afforded by the creamometer are, however, far from reliable. Cream is really milk rich in fat, caseine, etc., and the quantitative relation it bears to the true amount of fat present is not always a direct one. A recent form of lactoscope, devised by Feser, is less objectionable, and is in very general use for the rapid estimation of fat in milk. It consists essentially of a glass cylinder, provided with two scales, one being graduated into c.c., the other, into percentages of fat. In the lower end of the instrument is a contraction, in which is placed a cylindrical piece of white glass, graduated with well-defined black lines. In using the lactoscope, 4 c.c. of the milk are introduced into the instrument by means of a pipe tte, and water is gradually added, with shaking, until the black marks on the small white cylinder become just visible. Upon now referring to the c.c. scale, the quantity of water used to effect the necessary dilution is ascertained, and the corresponding percentage of fat in the sample is indicated by the percentage scale.*

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 con

* For description of the "Lactocrete," see 'Analyst,' Jan. 1887.

The

and

stantly 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. several filtrates are collected in a tared beaker, 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. been determined by experiment, that every percentage of milk-solids not fat, increases the specific gravity of milk O'00375, whereas each percentage of fat decreases the gravity o 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

It has

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 The residue is dried until it ceases to decrease in sugar. 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 o 067 gramme of milk sugar.

The sugar in milk can also be estimated by the polariscope (see under Sugar, p. 112). In case the VentzkeScheibler instrument is used, 65 36 grammes of the sample are weighed out and introduced into a 100 cc. flask; about 5 cc. of plumbic basic acetate solution is added, and the liquid is well shaken, and then allowed to stand at rest for a few minutes. It is next filtered, its volume made up to the 100 cc. mark, and the 20 cm. tube filled and the reading made; this divided by 2 gives the percentage of sugar in the milk.

Mr. A. Adams has recently proposed a method of milk analysis which consists in first placing 5 cc. of the sample in a tared beaker, and then introducing a weighed paper coil made of blotting paper from which all fatty matter has previously been removed by washing with ether. As soon as the milk is completely absorbed, the paper coil is removed and dried at 100°. The increase of weight gives the amount of total solids. The fat is next extracted by petroleum naphtha or ether, and its weight determined. The proportion of solids not fat is ascertained by again drying and weighing the exhausted coil.

The standards adopted by the English Society of Public Analysts for pure milk, are :

In the State of New York, the legal standards for milk are that it shall not contain more than 88 per cent. of water, nor less than 12 per cent. of milk solids, and 3 per cent. of fat.

In Massachusetts the law fixing a chemical standard of purity for milk reads: "In all cases of prosecution, if the milk shall be shown upon analysis to contain more than 87 per cent. of water, or to contain less than 13 per cent. of milk solids, it shall be deemed, for the purpose of this Act, to be adulterated."

The Board of Health of New Jersey fixes the minimum amount of total solids at 12 per cent. and the maximum amount of water at 88 per cent. In Paris, the minimum limits for condemnation are the following:

Fat, 2.70; milk-sugar, 4'50; caseine, albumen, and ash, 430; total solids, 1150.

The following proportion can be employed in the calculation of the amount of pure milk (x) contained in a suspected sample :—

From the total solids :

12.5 total solids found = 100 : x.

From the solids not fat :

9 30 solids not fat = 100: x.

From the sugar:

4 40 sugar found = 100: x.

From the specific gravity :

1030 sp. gr. = 100: x.

In most cases the determination of the total milk-solids and the fat (the difference being the solids not fat) furnishes all the data required for determining the amount of watering which a sample of milk has undergone. The Society of Public Analysts use 9 as the average percentage of solids