Standards for Certified Milk. 265 



bacteriologist designated by the medical milk commission as to 

 temperature, odor, taste, and bacterial 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 milks or 

 creams as certified milks or creams, the range of variation for 

 such milks 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 Bab- 

 cock (a), the Leffmann-Beam (6), and the Gerber (c). 



(a) Babeock test. The Babeock test is based on the fact that strong sulphuric 

 acid will dissolve the nonfatty solid constituents of milk, and thus enable the fat to 

 separate on standing. It can be conducted by any of the Babeock outfits which are 

 purchasable in the market. 



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

 milk. To this is added, from a pipette, burette, or measuring bottle, 17.5 c. c. com- 

 mercial sulphuric acid of a specific gravity of 1.82 to 1.83. The contents 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 5 minutes at a speed of from 800 to 1,200 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 bottle is still hot. The reading 

 is from the upper limits of the meniscus. A pair of calipers 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 tfie 

 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 added and mixed. Then 9 

 c. c. of concentrated sulphuric acid is added in portions of about 1 c. c. ; after each 

 addition the liquids are mixed by giving the bottle a gyratory motion. If the fluid has 

 not lost all of its milky color by this treatment, a little more concentrated acid must 

 be added. The neck of the bottle is now immediately filled at about the zero point 

 with one part sulphuric acid and two parts water, well mixed just before using. Both 

 the liquid in the bottle and the diluted acid must be hot. The bottle is then placed at 

 once in the centrifugal machine; after rotation from one to two minutes, the fat will 

 collect in the neck of the bottle and the percentage may be read off. 



(c) Gerber' s test. This test is applied as follows: The test bottles are put into 

 the stand with the mouths uppermost; then, with the pipette designed for the purpose, 

 or with an automatic measurer, 10 c. c. of sulphuric acid are filled into the test bottle, care 

 being taken not to allow any to come in contact with the neck. The few drops remaining 

 in the tip of the pipette should not be blown out. Then 11 c. c. of milk are measured with 

 the proper pipette and allowed to flow slowly onto the acid, so that the two liquids mix 

 as little as possible. Finally, the amyl alcohol is added. (It is important to use the re- 

 agents in the proper order, which is sulphuric acid, milk, amyl alcohol. If the sulphuric 

 acid is followed by amyl alcohol and the milk last, then the result is sometimes incorrect.) 

 A rubber stopper, which must not be damaged, is then fitted into the mouth of the test 

 bottle, and the contents are well shaken, the thumb being kept on the stopper to prevent 



