PHYSICAL AND CHEMICAL EXAMINATION OF MILK 173 



ture. It is advised by some to straighten the top meniscus by 

 dropping a small amount of some liquid on the surface, but the 

 liquid used must not dissolve any part of the fat. Fat-saturated 

 alcohol can be used or glymol, which can be procured under the 

 commercial name of white mineral oil. The reading is rendered 

 more distinct if the oil is colored red by digesting some alkanet root 

 in it. Amyl alcohol, colored red, can be used for the same purpose. 



When the fat column is turbid and the acid- cream mixture 

 milky, accurate reading is difficult. In such cases the bottles 

 should be placed in hot water for about ten minutes, or, if this 

 procedure does not clarify the fat, the bottles can be placed in cold 

 water until the fat solidifies. After this the bottles may be placed 

 in hot water and the fat melted. 



Testing Skimmed Milk, Buttermilk, and Whey by the Babcock 

 Method. Testing skimmed milk, buttermilk, and whey for fat 

 by the Babcock method is feasible, although some slight modifi- 

 cations are necessary owing to the small fat content in these prod- 

 ucts. In separated milk and buttermilk the percentage of fat 

 is frequently less than 0.1 per cent., and, since it has been shown 

 that as much as 0.2 per cent, of fat may be lost sight of in the 

 Babcock test, greater accuracy is necessary in testing products 

 containing but 0.1 or less per cent. fat. Furthermore, it is diffi- 

 cult to read accurately 0.1 per cent, or less in milk-testing bottles. 



Attempts have been made to overcome these difficulties by 

 doubling the reading when the test shows less than 0.1 per cent. 

 This method obviously does not contribute to accuracy. The 

 most approved method of correcting the error is by the use of 

 special skimmed milk test bottles. These have necks of small di- 

 ameter so that the graduations are far apart. However, since it is 

 difficult to discharge the milk and acid through a narrow neck 

 without choking it with consequent loss of material, a second neck 

 has been provided in these bottles (Fig. 64). The fluids are poured 

 into the bulb of the bottle through this side neck. The fat is 

 forced into the narrow graduated neck, because the end of the side 

 tube is below the surface of the acid-milk mixture. A tightly 

 fitting cork may be placed in the mouth of the graduated neck and 

 pushed down until the lower line of the fat column coincides with 

 a mark so that reading is facilitated. 



It has been stated previously that some fat remains in the 

 acid mixture and that the smallest fat globules are difficult to 

 separate from the liquid by centrifugal force. This difficulty is of 

 greater importance when skimmed milk, buttermilk, or whey are 

 tested than when milk or cream is tested, since the relative number 

 of small globules is greatest in milk or milk products from which 

 the bulk of the fat has been removed. As much as 0.05 to 0.1 



