MILK-FAT. 21 



The fat globules were first discovered and described in 1697 by A. Von 

 Lesuwenhoeck. The number of these fat globules in a drop of milk varies ; 

 but it is almost impossible to count them. A conception of the fineness of 

 the state of division of the fat in milk is best obtained, so far as it is pos- 

 sible to measure it, by means of a simple calculation, from which we obtain 

 the following results, in the case of a sample of milk containing 4 per cent 

 of fat (taking the specific gravity of pure milk-fat as '924 at 17*5 C.): 



Diameter, in -01 mm. Diameter in -0016 mm. 



The weight of a globule, - '000,000,483,8 rag. '000,000,002,0 mg. 

 The number of globules in 1 



kilo, (approximately), - 80,000 millions, 20 billions. 



The surface area of the glo- 



bules in 1 kilo, of milk is 



approximately, 25 square metres, 157 square metres. 



If the diameter of the largest globule be 6 '25 times that of the smallest, 

 then its weight will be 244 times that of the smallest. 



The impetus 7 and <t> which a globule receives through its weight and 

 centrifugal force may be stated as follows: 



and = a' (f - l)- ( 2 6 ' *) 2 - r, u\ 



in which a, and a', indicate the respective coefficients of resistance, 8, and 

 <$', the viscosity of the milk serum and milk fat, g the acceleration due to 

 specific gravity, and TT the Ludolph number, r the radius vector, and u the 

 number indicating the circumference of the globule. The movement of 

 the fat globules in milk towards the cream layer in the ordinary rising of 

 cream, as also in the separation of cream by centrifugal force, is obviously 

 not an accelerated one, but is uniform throughout. The other animal fats, 

 which, in addition to milk-fat, act as foods, are chiefly made up of stearin, 

 palmitin, and olein; while milk-fat only contains, on an average, about 91 

 to 92 per cent of these neutral fats. The remaining 8 to 9 per cent prob- 

 ably consists of seven other neutral fats, among which butyrin and caproniu 

 predominate Other five, viz. caprylin, caprinin, laurin, myristin, and butin, 

 are present in very minute quantities, some of them in the most minute 

 traces. 



If pure butter-fat be saponified, and the butter so obtained be carefully 

 decomposed with sulphuric acid, as in the Hehner and Angell process, the 

 separation of the characteristic group of non-volatile and insoluble fatty 

 acids (stearic, palmitic, oleic, myristic, and butic acids), from the remaining 

 volatile and soluble fatty acids, can be easily effected, and their exact per- 

 centage determined. It is, however, impossible to estimate, even approxi- 

 mately, the percentage of the individual fats of either the non-volatile or 



