84 SCIENCE AND PRACTICE OF DAIRYING. 



then placed in the extraction apparatus and extracted for three hours, and 

 the weight of the fat extracted is estimated. If the roll after extraction 

 is once more dried for half an hour and is weighed, and the original weight 

 of the strip of paper is subtracted from the weight thus found, the weight 

 of the non-fatty solids is obtained. The sum of the non-fatty solids and 

 the fat gives further the total solids. 



Determination of Percentage of Nitrogenous Matter. This is carried 

 out according to the method recommended by Ritthausen, which is as 

 follows: 25 c.c. of milk are measured off, weighed, and diluted with 

 400 c.c. of water. 10 c.c. of a copper sulphate solution (69 -28 grams of 

 pure salt per litre) are added, and then 6*5 to 7 '5 c.c. of a potash solution 

 of such a strength that 1 volume of copper is precipitated for each 

 volume of the copper solution. The solution, after addition of the alkali, 

 must be neutralized with acid till it possesses a weak acid reaction, 

 and may contain a little copper in solution. The precipitate falls down 

 rapidly, so that the supernatant liquid can be quickly filtered through a 

 dried weighed filter, and the precipitate quickly washed by decantation and 

 brought on to the filter. The filtrate, along with the washing water, can 

 be used for the determination of milk-sugar; and the copper precipitate, 

 which, in addition to the entire mass of nitrogenous or proteid matter com- 

 bined with the copper, contains also all the fat which is in the milk, may be 

 used for the quantitative determination of the fat. In any case the fat has 

 to be extracted from the precipitate. For this purpose it is washed with 

 a small quantity of absolute alcohol, any particles of the precipitate 

 adhering to the filter being carefully removed with a platinum spatula, 

 and broken up as much as possible and extracted with ether, either on a 

 glass funnel or in the Soxhlet fat-extraction apparatus. If a quantitative 

 determination of the fat is desired, the alcohol and ether washings may be 

 evaporated and the residue weighed. The precipitate from which the fat 

 has been extracted is still further treated with absolute alcohol, and is dried 

 immediately afterwards until it becomes of a bright blue earthy colour, and 

 easily friable. It is then placed in the drying-bath at 125 C. until its 

 weight is constant. As soon as the weight is constant it is carefully 

 ignited, at first at a low heat, so that the easily combustible proteid sub- 

 stances in combination are entirely burnt off. From the loss in weight the 

 amount of albuminoids contained in the milk is estimated. This estima- 

 tion is liable to a small error (about -08 per cent), and is by that amount 

 too low, since in the ignition residue the sulphuric acid formed by the 

 oxidation of the sulphur of the albuminoids is estimated with it. It is 

 necessary to examine the ignition residue for its percentage of carbon, 

 and if any is found, to weigh it in a weighed filter-paper, and to calculate 

 it to the loss on incineration, which represents the proteid substances. 



