

DAIRY PRODUCTS. 101 



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begins at 5cin. from the top of the cylinder and is extended downwards. 

 Each mark is one-hundredth of the whole volume. Being filled with 

 milk to the zero point and allowed to stand twenty-four to forty-eight 

 hours, the percentage of cream is read directly on the scale. 



Since the volume of cream formed depends on the shape of the vessel 

 the temperature, and the time, this method is not reliable. This error 

 is reduced to a minimum by the use of a centrifugal machine for sepa- 

 rating the cream. A machine for this purpose has been constructed by 

 Lefeldt. 1 



In 1883 I saw a very convenient machine which had been constructed, 

 in the laboratory of the University of Illinois at Champaign. The appa- 

 ratus already described for separating the ether fat solution in Soxhletfs 

 method I have used with success in separating cream. The centrifugals 

 used in separating the cream from the milk in large dairies are con- 

 structed on the same principle. 



For a comparison of the numbers obtained by these processes with 

 those given by the gravimetric determination, I refer to Becke's mono- 

 graph. 2 



The Lactocrite. This name is given to an instrument invented by De 

 Laval 3 , designed to separate the fat in milk after appropriate chemical 

 treatment. 



The test vessels used iii this apparatus are cylindrical boxes made of 

 silvered metal, with accurately ground hollow silvered stoppers. These 

 stoppers are expanded at the bottom, and at the top are contracted, 

 and end in a small hole. They are joined to a glass tube of small inter- 

 nal diameter. This tube is furnished with a jacket by which it can be 

 screwed onto the stopper, and this jacket carries two longitudinal slits, 

 through which the divisions in the glass tube can be read. In the bot- 

 tom of the jacket is a hole, so that the glass tube and metal stopper 

 form a canal open at both ends. 



The centrifugal machine consists of a steel revolving disk. In the 

 upper part of this there is a circular cavity, extending from which, like 

 adii, are 12 holes to receive the test apparatus above described. 

 These holes dip slightly downward. The disk is incased with a jacket 

 having a removable cover, which prevents a too rapid fall of tempera- 

 ture during the operation. By means of appropriate apparatus the 

 disk can be driven at the rate of about 6,000 revolutions per minute. 



Preparation of the milk. In an ordinary test tube put equal portions 

 of the -milk to be tested and a mixture of 20 parts of concentrated 

 acetic and one part of sulphuric acid. The test tube is closed with a 

 cork in which is fixed a glass tube, shaken, and heated for ten to fifteen 

 minutes in a water bath with frequent shaking. 



1 Becko, op. cit., p. 43. 



2 Op. cit., pp. 40-45. 



3 Ding. Poly. J., vol. 261, p. 219; Chem. Centralblatt, 1886, p. 798. 



