Fig. 110. Gerber’s Butyrometers.
The apparatus have been greatly improved and simplified since the first description of them was published and have come into extensive use in Europe and to a limited extent in this country.[470]
The butyrometer tubes are made of various sizes and shapes, but the most convenient are those noted above as shown in [Fig. 110].
Before adding the strong sulfuric acid, one cubic centimeter of amyl alcohol is mixed with the milk in the butyrometer. This admixture serves to clarify the fat and render the reading more easy.
The centrifugal is run by hand, and the required speed of rotation is given it by means of a cord wrapped spirally about its axis, as shown in [Fig. 111]. The cord in the new machines is replaced by a leather strap working on a ratchet.
Fig. 111. Gerber’s Centrifugal.
The process is more speedy than that of Babcock, and the results have been shown by a large experience to be reliable and accurate.
The sulfuric acid employed is of 1.825 to 1.830 specific gravity. There is no danger of loss by the formation of volatile ethers where the quantity of amyl alcohol used does not exceed one cubic centimeter. In a comparison of the respective merits of the methods of Babcock, Thörner and Gerber, made by Hausamann, the first place is awarded to the Gerber process.[471] In the [figure 110], the butyrometers marked 2, 5 and 8 are for milk, and those numbered 1, 3 and 7 are for cream and cheese. In conducting the analysis, ten cubic centimeters of the sulfuric acid are placed in the butyrometer with one cubic centimeter of the amyl alcohol. When mixed, eleven cubic centimeters of the milk are added and the contents of the tube well mixed, the tube stoppered and placed in the centrifugal. The larger tubes, open at both ends, require double the quantities of the reagents mentioned. The measurements are made at about 15°.
Minute directions for conducting the analyses with milk, skim milk, buttermilk, cream, condensed milk, cheese and butter accompany each apparatus.