106 REPORTS ON THE STATE OF SCIENCE.—1918. 
fat globules bear a “condensed layer” which is very tenaciously 
held. The rising of the fat globules is thus inhibited and no cream 
Separates. Again, one cannot churn homogenised milk, since churn- 
ing really implies the coalescing of the fat particles, and the separa- 
tion of the milk serum. 
The density of milk suffers no change on homogenising. The 
viscosity increases, due to casein adsorption by the fat globules, and 
the milk is thicker than ordinary milk of the same fat content. 
Wiegner reduced the average diameter of fat particles in milk by 
homogenising from 2°9 to about 0°27. From viscosity measure- 
ments he calculated that in ordinary milk about 2 per cent. of the 
casein is adsorbed, whilst the casein adsorbed by the fat in homo- 
genised milk is about 25 per cent. 
No change is produced in the molecular disperse constituents of 
the milk, as is indicated by the fact that the electrical conductivity, 
and the osmotic pressure (determined by F. Pt.) show no change. 
If the homogenised milk is kept at a low temperature for some 
time the viscosity rises, and the fat particles do aggregate somewhat. 
Skim milk cannot be homogenised since it is nearly fat-free, and the 
casein present is already in a high degree of dispersity. Although 
mechanical means are of no avail, chemical means allow of this fur- 
ther dispersion of the casein, e.g., when NaOH is added to skim 
milk, the viscosity increases rapidly with the concentration of the 
alkali. 
Homogenised Cream. 
When cream is forced through an homogenising machine at a 
pressure of from 3,000 to 4,600 lbs. per square inch, the fat particles 
become extremely small, and the product is very viscous. Separation ~ 
of the fat again is rendered almost impossible, even on centrifuging ; 
also it admits of neither churning nor whipping, and a colloid 
substance such as gum tragacanth must be added (e.g., 0° 1 per cent.) 
before a permanent foam can be produced. (Cf. Koll. Zeit., 15, 
105-123 (1914).) Owing to its excessive thickness, homogenised 
cream is utilised in making ice-cream, since a cream containing 
about 17 per cent. of fat will, if homogenised, serve in an ice-cream 
as effectively as an ordinary cream of fat content 25 per cent., the 
final product having as good a body and texture, as well as 
“creaminess.”” An objection to homogenised cream is its peculiar 
“starchy” flavour, this being more apparent, the higher the tem- 
perature at which homogenisation is conducted. 
The surface tension of homogenised milk is lower than that of 
the normal sample of milk. 
Artificial Milk. 
Of late years artificial milk has been prepared, and numerous 
patents taken out in this connection. It is simple enough to make a 
solution containing all the inorganic constituents of milk, but the 
organic (colloidal) constituents present a more difficult problem. 
Certain nuts and beans contain proteid substances closely akin to 
gluten or casein in properties, e.g. soya beans contain abont 37 per - 
cent. of such proteid matter, which can be brought into. colloidal — 
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