INDIRECT METHODS. 151 



a method whereby the use of sulphuric acid is avoided, and this 

 has found favour among those persons who have not had the 

 advantage of a laboratory training. 



The composition of the alkaline salt solution has not been 

 made public ; the method is employed with the same apparatus 

 as the acido-butyrometric method. 



Eleven c.c. of the alkaline salt solution, 10 c.c. of milk, and 

 0-6 c.c. of iso butyl alcohol are placed in a butyrometer, which is 

 closed with a stopper, and the contents mixed, and immersed in 

 water at 45 for three minutes, and after shaking the tube is 

 centrifuged, and the fat read off after placing again in water 

 at 45. These results are the same as those given by the acido- 

 butyrometric method, but the accuracy is somewhat less. The 

 amount of isobutyl alcohol added must not be varied. 



Sichler's sinacid method is very similar ; 10 c.c. of salt solution, 

 containing 15 per cent, of trisodium phosphate and 1 per cent, 

 of trisodium citrate, 10 c.c. of milk, and 1 c.c. of isobutyl alcohol 

 are placed in a butyrometer, and mixed well. The mixture is 

 heated to 75 to 90, again mixed well, and centrifuged for one 

 minute. The tube is placed in water at 70, and the fatty layer 

 read off. The isobutyl alcohol is usually coloured, and the 

 colour passes into the fatty layer, facilitating reading. 



Indirect Methods. 



Estimation of Cream. One of the earliest and simplest 

 methods of estimating the fat in milk is to allow the milk to 

 stand, and to measure the volume of cream thrown up. For 

 this purpose a creamometer or cylindrical vessel, the upper 

 portion of which is divided into spaces, each representing the 

 T ^th part of the total volume up to the highest line, is employed 

 (see Fig. 7, p. 75). It is filled to the mark, and allowed to 

 stand at rest for some time six, eight, twelve, or twenty-four 

 hours and the volume of cream measured. A good milk should 

 throw up about 10 per cent, of its cream in eight hours. 



The method is of very slight value for a determination of the 

 fat in milk, as comparatively slight variations in the conditions 

 make enormous variations in the volume of cream. Thus, the 

 author has found that milk freshly drawn and not cooled 

 containing 5-3 per cent, of fat threw up 25 per cent, of cream in 

 six hours, while another milk with the same percentage of fat, 

 which had been raised to the boiling point and cooled, only 

 threw up 2 per cent, of cream in the same time. These, of course, 

 are extreme instances, and it is found in a majority of cases that 

 the percentage of cream thrown up in six to eight hours divided 

 by 3 will give an approximation to the percentage of fat. 



