SCIENCE AND INDUSTRY. 
The chemical nature of milk is better known than its physical con- 
stitution. The chief constituents of cow’s milk of average quality may 
be stated as follows :— 
1. Water .. om ue Sa gta ... 87-2 per cent. 
Fae) OF: Ae . ae fie © BP Enea, 
3. Proteins (total) .. oj 3-6 per cent. 
(a) Caséinogen 8 per cent. 
(b) Lactalbumin, -5 per cent. > 9-1 per cent. 
_ 4, Milk sugar ‘ 4-8 per cent. \ 
5. Mineral matter .. we sper cent 
Total ae ents LUOg0 spemeceliis 
Another way of stating this is: Total solids, 12-8 per cent., of which 
the non-fatty solids form 9-1 per cent., and the fat 3-7 per cent. of the 
total weight of the milk. ; 
The fat is present in milk in the form of an emulsion, but not a per- 
fect one, as, on standing, it rises on account of its lower specific gravity 
(-92), and forms the cream layer. It is also readily separated by the 
centrifugal action of the separator, and its physical condition is altered. 
It is thought that each droplet is surrounded by a membrane, in which 
are distributed minute particles of the chief protein of milk, viz., 
caseinogen. This is present in eolloidal suspension, and acts the part 
of stabilizer in the system of water (the dispersing agent), oil drops, ° 
and proteins. The other protein, lactalbumin, is sometimes known as 
whey protein. It is not precipitated by acids along with casein, and 
it is not coagulated by rennin. Caseinogen is a complex phospho- 
protein, combined with a calcium salt, and is readily precipitated by 
acids or salts. It then forms the insoluble casein or acid curd. The 
curd formed by rennin is slightly different in composition, and. is a 
sweet curd—paracasein—which will not form in the absence of a soluble 
calcium salt. In cheese manufacture, the paracasein usually encloses 
most of the fat with it, so that there is a wide difference between the 
whey of the cheese vat and the buttermilk after butter making. On 
this account, 97 per cent. of butter consists of fat (883 per cent.) and water 
(13 per cent.), whereas fresh cheese consists of water, fat, and proteins |. 
(total 94 per cent.), in the ratio of 387 : 33 : 23 per cent. respectively. 
The sugar present is lactose or milk sugar, and unlike the proteins, it 
is in true solution. Hence, after the various operations of butter or 
cheesemaking, or casein manufacture, it is still in solution, and can be 
recovered. When milk is kept for some hours, the lactose becomes 
converted chiefly to lactic acid by th® fermentation action of lactic or | 
other bacilli. When the percentage of acid produced reaches about 0-8, 
the milk “sours,” and casein is precipitated by the lactie acid. By 
the fermentation of lactose in whey, lactic acid may be produced. 
Every 6 Ibs. of butter-fat by the Babcock test will yield about 7 lbs. 
of manufactured butter. The difference between the two is known as 
the overrun, and usually goes to the credit of the factory. In cheese 
manufacture, suppliers are generally paid on the fat test also, as there 
is a parallelism in the variation of fat and protein; milks with high 
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