THE MILK. 415 



phate or sodium sulphate in substance. The albumin is filtered off 

 and purified as described on page 316. 



Quantitative Estimation of the Total Albumins. To this end, a few 

 grammes of milk are diluted with water, treated with a small 

 amount of sodium chloride solution, and precipitated with tannic 

 acid or phosphotungstic acid in excess. In the precipitate, which is 

 washed with water, the amount of nitrogen is then estimated by 

 Kjeldahl's method. By multiplying the result by 6.37 in the case 

 of cows' milk, or by 6.34 with human milk, the corresponding 

 amount of albumin in ascertained. The nitrogen of some of the 

 extractives is included in the result, but may be ignored. In cows' 

 milk it represents about one-sixteenth of the total amount of nitro- 

 gen, and in human milk about one-eleventh. 



Separate Estimation of the Casein and the Soluble Albumins. A 

 few grammes of milk are diluted with two or three volumes of a 

 saturated solution of magnesium sulphate, and are then saturated 

 with the salt in substance. In the precipitate, which is washed with 

 a saturated solution of the salt, the nitrogen is then determined as 

 above. The result multiplied by 6.37 indicates the amount of 

 casein. The amount of lactalbumin can be ascertained by deduct- 

 ing the value found for casein from the total amount of albumin, or 

 by diluting the filtrate, after separation of the casein, precipitating 

 with tannic acid, and determining the amount of nitrogen as before. 

 In this case also we multiply by 6.37. 



The results for casein thus obtained are not absolutely accurate, 

 as the globulin is likewise precipitated by magnesium sulphate. 

 Its amount, however, is so small that it may well be disregarded. 



The Fats. The fats which are found in the milk, viz., in butter, 

 are essentially the same as those which occur elsewhere in the 

 animal body, viz., stearin, palmitin, and olein. In addition, how- 

 ever, we also find small amounts of the triglycerides of myristinic 

 acid, butyric acid, and capronic acid, and traces of caprylic acid, 

 caprinic acid, laurinic acid, and arachinic acid. 



Stearin, palmitin, and olein constitute about 98 per cent, of the 

 total amount, and of these, olein represents about 29.439.2 per 

 cent. As a consequence of the large quantity of olein which is 

 thus present, the melting-point of butter is relatively low, viz., 

 31-34 C., while it solidifies between 19 and 24 C. 



In addition to the neutral fats, butter also contains about 7 per 

 cent, of volatile fatty acids, of which 3.75.1 per cent, are repre- 

 sented by butyric acid and 23.3 per cent, by capronic acid. 



Formic acid has been found in butter which had been exposed to 

 sunlight. 



Of the origin of the fats which are found in milk we know that 

 they are to a large extent derived from albumins, and I have already 

 pointed out that their amount increases with a diet that is rich in 

 such material, oven though no fat is ingested at all. They diminish 



