632 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



The cream maybe roughly determined in milk by placing it in a tall cylindrical 

 glass, graduated into one hundred parts The milk should be allowed to stand in 

 this creamometer for twenty-four hours and the volume of cream separated on the 

 surface may then be determined, one gramme of cream equaling about 0.2 

 grammes of fat. Good cows' milk should separate from ten to fifteen volumes of 

 cream. This method is, however, not thorouhgly reliable, since different speci- 

 mens of milk will throw up their cream with different degrees of readiness. The 

 second method, and a much more reliable one, of determining the amount of fat 

 or cream present is, by means of the lactoscope. This instrument consists of a 

 little cup with two of its sides formed of two parallel plates of glass, distant from 

 each other half a centimeter. For applying this test, in addition to such a glass, 

 a jar graduated to one hundred cubic centimeters and a pipette of three cubic 

 centimeters are needed. Three cubic centimeters of milk are taken and shaken 

 up well with one hundred cubic centimeters water, and the mixture then placed 

 in the glass cup with the parallel sides and a lighted stearin candle placed one meter 

 from it in a dark room. If at the first experiment the contour of the flame can be 

 seen, the milk is poured back into the large measure and a further measured quantity 

 of undiluted milk added until the contour of the candle-flame is entirely obscured. 

 The percentage of fat is then determined by the following formula : If x equal 

 the percentage of fat and n the number of cubic centimeters of milk required, then 



23 2 

 x equals — ^ + 0.23. Thus, if three cubic centimeters of milk were required to 



23 2 

 obscure the light, the formula would read : x= — ^-f-0.23, ors = 7.96, the per 



o 



cent, of fat in the milk. Six cubic centimeters of pure cows' milk with one hun- 

 dred cubic centimeters water should form a mixture which will obscure the candle- 

 flame ; if more milk is required, then the milk has been diluted. Thus, twelve 

 cubic centimeters indicate 50 per cent, water, and eight cubic centimeters about 

 30 per cent, water. The following table gives the percentages of fat in the milk 

 when the candle-flame is obscured by different amounts of milk in Vogel's galacto- 

 scope : — 



3 cnbic centimeters of milk indicate . 7.96 per cent, of fat. 



3.5 '• " '■ " 6.86 



4.0 '■ '■ " '• . 6.03 



4.5 '■ '• '■ 5.38 



5.0 " '■ '■ " 4.87 



5.5 " " " 4.45 



6.0 " '■ ' '• 4.09 



6.5 " '■ " '• 3.80 



7.0 '■ ' " " 3.54 



7.5 " " " •• 3.32 



8.0 ' •■ ■■ '• 3.13 ' 



8.5 " ■• ■' " 2 96 - 



9.0 " " ■■ " 2.80 



9.5 " » •• " 2.77 



10.0 •• " " '• 2.56 " 



11.0 " '• • '• 2.43 ' 



12.0 '■ ' " '• 2.16 ■ 



13.0 " ' '■ " 2.01 ' 



14.0 " ' " . 1.80 • 



Another ready method of estimating the fat in milk is by means of Marchand's 

 lactobutyrometer. As improved by Caldwell and Parr {Airier. Chem. Journ., Nov. 

 1885), this method is performed as follows : — 



The instrument employed consists of a thick glass tube, open at each end, 

 with a stem six cubic centimeters in diameter and twenty-three centimeters long, 

 graduated in S V cubic centimeter, and a bulb about eight centimeters in length, 

 and of such a capacity that in passing from the lowest graduation on the stem 

 to the inner end of the stopper in the lower mouth one passes from five to thirty- 

 three cubic centimeters. Then the ether-fat solution will always come within the 

 range of the graduation on the stem. Closing the lower mouth with a good cork, 

 ten cubic centimeters of the well-mixed sample of milk are delivered into the 

 well-dried tube from a pipette, then eight cubic centimeters of ether (Squihb's 

 stronger) and two cubic centimeters of 80 per cent, alcohol. Close the smaller 

 mouth of the tube with a cork and mix the liquids by thorough shaking (not 

 violently nor prolonged). Both corks should be held in place by the fingers 

 during this operation, and the upper one should be once or twice carefully 



