MILK 



79 



test-bottles are allowed to stay 3-5 minutes in the warm 

 water-bath ; they are then shaken and whirled in a centrifuge, 

 Gerber's for example, for 2-3 minutes. 



When the tubes are taken from the centrifuge they are again 

 placed in water of a temperature of 45 C. for a few minutes, 

 and then read in the same way as the Gerber tubes, the column 

 of fat being brought to zero on the scale by carefully screwing 

 in the stopper. The percentage amount of fat can then be 

 read off directly, each division of the scale corresponding to O'l 

 per cent. 



The cleaning of the test-bottles is very simple ; all that is 

 required is to shake them and then to empty whilst warm. 

 They can then be washed with water alone, no soda or brush 

 being required. 



This method has undoubted advantages over the acido- 

 butyrometric one, for the corrosive sulphuric acid is not needed 

 and instead of the evil-smelling amyl alcohol, the sinol (which 

 has a pleasant, fruit-like odour) is used. The test-bottles also 

 do not become hot when shaken. According to experiments 

 made by the author ; the results are quite equal to those of 

 Gerber's method, and compare very closely with those got by 

 gravimetric analysis. There is no formation of a plug of 

 material below the fat, it being separated sharply, as a beauti- 

 fully coloured clear column, from the liquid. Equally good 

 results are obtained from sour milk or from milk which has been 

 preserved with potassium bichromate or formalin, provided very 

 large quantities of preservative have not been used. Sour 

 milk should first be made fluid by the addition of a drop or two 

 of strong caustic soda or caustic potash. The method with 

 ammonia does not give satisfactory results. 



The Sinacid method in its present form can be regarded as 

 an excellent practical form of determining the percentage of 

 fat in milk. For separated milk, however, it is just as unsuit- 

 able as the methods previously mentioned. Test-bottles which 

 have a capillary graduated tube, and are intended for the 

 analysis of separated milk and butter-milk, can be obtained, 

 but with them the results are also unsatisfactory, at least with 

 separated milk. 



