The author, after criticising the various methods for estimating fat in milk which have been proposed from time to time, agrees with Stokes (_Analyst_, 1885, p. 48), Eustace Hill (_Analyst_, 1891, p. 67), and Bondzynsky (_Landwirth Jahrb. der Schweiz_, 1889), that the method of Werner Schmid is the simplest, most rapid, and convenient hitherto introduced. The conditions tending to inaccuracy are: The employment of ether containing alcohol; boiling the mixture of milk and acid too long, when a caramel-like body is formed, soluble in ether; the difficulty of reading off the volume of ether left in the tube, owing to the gradations of the instrument being obscured by the flocculent layer of casein; when only a portion of the ether is used, fat may be left behind in the acid mixture, as shown by Allen (_Chem. Zeit._, 1891, p. 331). The author believes that by the invention of the simple apparatus represented in the accompanying figure, he has rendered the process both accurate and convenient. This consists of a flask B of about 75 c.c. capacity, which has a glass tap fused on, with two capillary tubes attached, the one passing upward, the other downward. The neck of flask B is ground into the neck of flask A, which holds about 90 c.c. Either of the flasks can be placed in communication with the external air by the opening _a_. The ether must be previously washed with one or two tenths of its volume of water, to remove traces of alcohol. The operation is performed as follows: 10 c.c. of well mixed milk are weighed in (or measured into) flask A, 10 c.c. of hydrochloric acid added, and the mixture heated to boiling on an asbestos sheet. The boiling must not exceed a minute and a half, the fluid being shaken from time to time, and not allowed to become of a deeper color than a dark brown [not black]. The flask is cooled, and 25 c.c. of ether added. The two flasks are connected as shown in the figure, the tap closed, and the whole shaken for a few minutes, the flask being vented two or three times by the opening _a_. The apparatus is now inverted, allowed to stand five or six minutes, the tap turned, and the dark acid liquid drawn off into flask B. By a little shaking of the ether the whole of the acid liquid may be easily got into the lower flask. The apparatus is again inverted, then separated, 10 c.c. of ether are introduced into the flask B, the tap closed, and the fluids well shaken. When the ether layer is distinct, the acid liquor is run off, and the ether solution transferred to A. The whole of the ether solution is washed in the apparatus two or three times with a little water, the flask A removed to the water bath, the ether driven off, the last traces of ether and water being removed by placing the flask in a drying oven heated from 107 to 110 deg. C., where it must remain at least twenty minutes. The usual cooling in the exsiccator and weighing concludes the operation. Examples are