88 REPORTS ON THE STATE OF SCIENCE.—1917. 
Both egg albumin and blood albumin are used for clarifying or ‘ fining ’ 
liquids. They owe their special functions to the fact that on heating, 
or by action of acids or tannin, the coagulum forms upon and around 
finely divided suspended matter; at the same time impurities may be 
adsorbed so that the liquids after settlement or filtration remain quite 
clear and bright. 
Albumin or white of egg is used in baking for the preparation of light 
pastry, in which its film-producing properties are of great service. 
Albumin is also very useful for glazing purposes and in the manu- 
facture of leather finishes. (For the composition of leather finishes and 
the materials used in their manufacture see ‘ Leather Dressing,’ by M. C. 
Lamb, pp. 263-282, also M. C. Lamb and A. Harvey, ‘ Jour. Soc. Dyers and 
Colourists,’ 1917, 19.) 
Egg-yolk, although it contains 33 per cent. of fatty matter, is also 
an albuminous product, seeing that it contains more albumin than egg- 
white, e.g., about 15 per cent. It also contains about 1 per cent. of a 
carbohydrate and 1 per cent. of mineral matter. It is probably one of the 
most perfect emulsions known, since, however long it is kept, it shows 
no sign of separation or even on centrifuging or after considerable dilution. 
The albumin in egg-yolk, however, is not the same as that in the white, but 
consists, according to Gobley, of vitellin, nuclein, and cerebrin. 
Egg-yolk is always slightly acid to phenol-phthalein, although alkaline 
to methyl orange, the alkalinity equalling about 0-87 per cent. of NaHO. 
Egg-yolk is a very efficient emulsifying agent, being often used for this 
purpose. This property is, no doubt, due, partially at any rate, to the 
presence of lecithin in the fatty material; the amount of lecithin in the 
yolk equals about 10 per cent. Egg-yolk is employed in the preparation 
of ‘fat liquors’ for treating leather (‘Leather Dressing,’ by M. C. Lamb, 
pp. 214-228, also H. R. Procter, “ Leather Industries Laboratory Book,’ 
1908, p. 353), also in the manufacture of embrocations, being capable of 
emulsifying such incompatibles as acetic acid and olive oil or turpentine. 
Certain salts, e.g., NaCl, KCl, and KNOs, cause a dispersion of the albu- 
min in egg-yolk, the material becoming almost transparent. The same 
effect is produced with HCl, only that after a time the material sets to a 
gel and subsequently becomes opaque. ‘Salted yolks,’ that is, yolks 
containing about 10 per cent. of common salt, are an article of commerce. 
Yolk of egg was one of the earliest mediums used in painting, being 
employed in ancient times as a medium for laying on the pigments in 
tempera painting. A. H. Church (‘Chemistry of Paints and Painting,’ 
18Y2, p. 65) states that after a time the yolk becomes insoluble, the change 
being hastened by exposing the painting to sunlight, a practice which 
was quite common. Desiccated egg and yolk dried at a temperature of 
100° F. also become gradually insoluble on keeping, this change being 
accelerated by heating at 100° F. or over, light not being necessary. 
Casein. 
Casein is the albuminoid of milk, which contains about 4 per cent., 
and in which it plays the part of an emulsifier, although in this respect 
it is not a perfect agent, seeing that milk separates on standing into two 
phases, the cream and skimmed milk. Cream separated by the centrifugal 
machine, however, is a perfect emulsion in which both the fat and casein 
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