504 MILK 



too small to be seen with the naked eye or with slight magnification shall not 

 be considered in the count. 



69. Records of Bacteriologic Tests. — The results of all bacterial tests shall 

 be kept on file by the secretary of' each commission, copies of which should 

 be made available annually for the use of the American Association of Medical 

 MUk Commissions. 



Chemical Standards and Methods 



The methods that must be followed in carrying out the chemical investi- 

 gations essential to the protection of certified milk are so comphcated that in 

 order to keep the fees of the chemist at a reasonable figure, there must be 

 eliminated from the examination those procedures which, while they might 

 be helpful and interesting, are in no sense necessary. 



For this reason the determination of the water, the total solids, and the 

 milk-sugar is not required as a part of the routine examination. 



70. The chemical analyses shaU be made by a competent chemist desig- 

 nated by the medical milk commission. 



71. Method of Obtaining Samples. — The samples to be examined by the 

 chemist shall have been examined previously by the bacteriologist designated 

 by the medical milk commission as to temperature, odor, taste, and bac- 

 terial content. 



72. Fat Standards. — The fat standard for certified milk shall be 4 per 

 cent., with a permissible range of variation of from 3.5 to 4.5 per cent. 



73. The fat standard for certified cream shall be not less than 18 per cent. 



74. If it is desired to sell higher fat^percentage mUks or creams as certi- 

 fied milks or creams, the range of variation for such mUks shall be 0.5 per 

 cent, on either side of the advertised percentage and the range of variations 

 for such creams shall be 2 per cent, on either side of the advertised percentage. 



75. The fat content of certified milks and creams shall be determined at 

 least once each month. 



76. The methods recommended for this purpose are the Babcock (a), 

 the Leffmann-Beam (b), and the Gerber (c). 



(a) Babcock Test. — The Babcock test is based on the fact that strong 

 sulphuric acid will dissolve the non-fatty solid constituents of milk, and thus 

 enable the fat to separate on standing. It can be conducted by any of the 

 Babcock outfits which are purchasable in the market, 



''The test is made by placing in the special test bottle 18 grams (17.6 c.c.) 

 of milk. To this is added, from a pipet, buret, or measuring bottle, 17.5 c.c. 

 commercial sulphuric acid of a specific gravity of 1.82 to 1.83. The con- 

 tents of the bottle are carefully and thoroughly mixed by a rotary motion. 

 The mixture becomes brown and heat is generated. The test bottle is now 

 placed in a properly balanced centrifuge and whirled for five minutes at a 

 speed of from 800 to 1200 revolutions per minute. Hot water is then added 

 to fill the bottle to the lower part of the neck, after which it is again whirled 

 for two minutes. Now, enough hot water is added to float the column of 

 fat into the graduated portion of the neck of the bottle, and the whirling is 

 repeated for a minute. The amount of fat is read while the neck of the bot- 

 tle is still hot. The reading is from the upper limits of the meniscus. A 

 pair of cahpers is of assistance in measuring the column of fat." (Jensen's 

 Milk Hygiene, Leonard Pearson's translation.) 



(6) Leffmann-Beam Test. — The distinctive feature is the use of fusel oil, 

 the effect of which is to produce a greater difference in surface tension between 

 the fat and the liquid in which it is suspended, and thus promote its readier 

 separation. This effect has been found to be heightened by the presence of 

 a small amount of hydrochloric acid. 



The test bottles have a capacity of about 30 c.c. and are provided with a 

 graduated neck, each division of which represents 9.1 per cent, by weight 

 of butter-fat. 



Fifteen centimeters of the milk are measured into the bottle, 3 c.c. 

 of a mixture of equal parts of amyl alcohol and strong hydrochloric acid 



