BY DR. LAUDER BRUNTON. 529 



phates and carbonates of the alkaline and earthy bases. They 

 can only be investigated in the ash. For the method of igni- 

 tion see 214. 



Fats. The fats may be separated by either of the following 

 methods : 1. Evaporate the mixture of alcohol and ether with 

 which the coagulum was exhausted, and the fat remains. 



2. Add to 15 or 20 c. c. of milk, 10 c. c. of a moderately strong 

 solution of caustic soda; shake it vigorously with twice or 

 thrice its volume of ether. Remove the layer of ether, and 

 evaporate it in a water bath, and the fat remains. Ether does 

 not remove the fat from fresh milk, as the casein envelops the 

 globules, and protects the fat from its action ; but soda dis- 

 solves these envelopes. Ether will remove 90 per cent, of the 

 butter from milk which has become acid by standing. 



** 180. Mode of Estimating the Quantity of Butter 

 Contained in Milk. A rough method of doing this, is to 

 measure the cream which separates from it by Chevallier's cre- 

 mometer. This is a cylindrical vessel, graduated into a hun- 

 dred parts. The percentage amount of cream is indicated by 

 the number of divisions it occupies when the vessel is filled with 

 milk to the zero point. This method is quite unreliable. 



VogeVs Test. A much more exact method is that devised 

 by Vogel, which depends on the fact that the opacity of milk 

 is due to the globules it contains, and is in proportion to their 

 number. 



The apparatus required for this test are 1. A cylindrical 

 bottle, in which to mix the milk and water. It should hold 

 about 200 c. c., and have a mark on the side at the height of 

 100 c. c. 2. A test-glass, with parallel glass sides, exactly ^ a 

 centimetre apart, and supported vertically on a metal foot. 3. 

 A pipette graduated in fifths of a cubic centimetre. 



Application of the Test. Before applying this test, it must 

 be ascertained by microscopical examination that the milk does 

 not contain starch granules, or any other impurity in suspen- 

 sion which might increase its opacity. Fill the bottle up to 

 the 100 c. c. mark with clear spring water. Fill the pipette up 

 to zero with milk (App. 217), and let 3 c. c. run into the bottle. 

 Mix it well with the water, and fill the test-glass with the mix- 

 ture. Put it in a tolerably dark room, place a stearine candle 

 at a distance of about three feet from it, and look at the candle 

 through the glass. If the contour of the flame can be readily 

 perceived, pour the liquid back into the bottle, add another 

 c. c. of milk to it, shake it, and look at the candle through it 

 again. Repeat this till the outlines of the flame can no longer 

 be recognized. Then add together the different quantities of 

 milk, so as to find the total amount which has been added, and 

 then ascertain by the following table how much butter the milk 

 contains : 

 34 



