120 METHODS OF ANALYSIS. 



(b) PAPER COIL METHOD. OFFICIAL. 



Make coils of thick filter paper, cut into strips 6.25 by 62.5 cm, and thoroughly 

 extract with ether and alcohol, or correct the weight of the extract by a con- 

 stant obtained for the paper. From a weighing bottle or weighing pipette 

 transfer about 5 grams of milk to the coil, care being taken to keep the end of 

 the coil held in the fingers dry. Dry the coil, dry end down, on a piece of glass 

 t the temperature of boiling water for one hour, or, better, in hydrogen at the 

 temperature of boiling water ; transfer to an extraction apparatus, and extract 

 with absolute ether or petroleum ether boiling at about 45 C. ; dry the ex- 

 tracted fat and weigh. 



(c) VOLUMETRIC METHODS. OFFICIAL. 



Babcock's or Gerber's centrifugal methods may be used. Following is the 

 Babcock centrifugal method : 



( 1 ) APPARATUS. 



(a) Babcock milk-test bottles, graduated to 10 per cent. 



(6) A centrifuge with sockets for from 2 to 32 bottles, according to the num- 

 ber of tests to be made, and capable of being run at a speed of from 600 to 1,200 

 revolutions per minute, according to the diameter of the machine. If many tests 

 are made steam turbine testers or electrical testers will be found convenient. 



(c) Pipettes, 17.6 cc. 



(d) Graduates, 17.5 cc, or a Swedish acid bottle delivering that amount, foi 

 measuring sulphuric acid. 



(2) DETERMINATION. 



Pipette off 17.6 cc of the carefully mixed sample into a test bottle and a( 

 37.5 cc of commercial sulphuric acid (specific gravity, 1.82-1.83). Mix, am 

 when the curd is dissolved whirl the test bottles in the centrifuge for foiu 

 minutes at the required speed for the machine used. Add boiling hot water, 

 filling to the neck of the bottles, and whirl for one minute; again add boiliuj 

 water so as to bring the fat within the scale on the neck of the bottles, ai 

 after whirling for one minute more read the length of the fat column, care 

 t:ikon to make the readings at a temperature between 130 and 150 F. when 

 the fat is wholly liquid. The readings give the per cent of fat in the milk 

 direct. 



For details as to the manipulation of the Babcock test and its application in 

 the analysis of dairy products other than milk the following books may be <-on- 

 sultcd : FaiTintfton and Woll, Testing Milk and Its Products, 18th edition, li)08,j 

 Madison, Wis., and Van Slyke, Modern Methods of Milk Testing, 1906, Nt 

 York. 



7. Detection of Added Water. Zeiss Immersion Befractometer Method.- 



Provisional. 



To 100 cc of milk at a temperature of about 20 C. add 2 cc of 25 per 

 acetic acid (sp. gr. 1.035) in a beaker; and heat the beaker, covered with M wat< 

 glass, in a water bath for twenty minutes at a temperature of 70 C. Place tl 

 beaker in ice water for ten minutes and separate the curd from the serum 

 filtering through a 12.5 cm folded filter. Transfer about 35 cc of the serum 

 one of the beakers that accompanies the control-temperature bath used in 

 nection with the Zeiss immersion refractometer, and take the refractomel 

 reading at exactly 20 C., using a thermometer graduated to tenths of a degi 

 A reading below 39 indicates added water; between 39 and 40 the sample 

 suspicious. 



