CASEINE , FIDRINE , JND GLUTEN.

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Some chemists admit the existence of two different kinds of caseine, oneof which is considered as capable of solution in water before coagulation.That which is called soluble caseine is always more or less contaminatedwith alkalies or salts, and attempts made to purify caseine by chemicalagents result in rendering the caseine much less soluble. It is generallyknown that milk is coagulated, that is to say, the caseine it contains insolution becomes, by the aid of a slight excess of alkali, solidified on theaddition of rennet or an acid, and also by the formation of la&ic acid (duringsouring of the milk), at the expense of a portion of the sugar of milk, thela&ic acid combining with the alkali and causing the precipitation of thecaseine.

Legumine, contained in the seeds of plants of the natural order of Legumitiosa,is closely approximate to, but not identical with, caseine.

Caseine finds many useful applications in the arts and industries. Mixedwith lime it is employed in decorative painting; it enters into the compositionof several kits and mastics; is used for glueing together the boxwoodemployed for woodcuts; dissolved in a solution of borax it constitutes a highlyadhesive glue, which is used in fine joiners’ work. A mixture of 6 parts ofcalcined magnesia and i part of oxide of zinc with sufficient caseine to makea paste yields, after desiccation, a perfectly white and very hard mass, whichadmits a high polish, and appears somewhat similar to meerschaum.

Under the name of ladtarine, caseine is employed as a mordant for fixingpigment colours; for instance, ultramarine. Under certain conditions theresults are moderately good, but great care and attention are required.La&arine is insoluble before use, and has to be dissolved in an alkaline liquid,such as ammonia or borax. The colours prepared with ladtarine are liable todecomposition, and a colour that may have worked well in the morning, inthe afternoon has been known to have changed either into a solid mass or acurdy conglomerate totally unfit for printing, and not re-convertible into goodcolour again by any means.

Several varieties of fibrine and gluten are known, but their chemicalcharacteristics do not exhibit great difference. The varieties are:—Fibrinespontaneously separated from venous blood; fibrine from arterial blood;fibrine from muscles; glutine, or Beccaria’s gluten after it has been exhaustedwith boiling alcohol. All these substances are insoluble in water; whenboiled in water under pressure in a Papin’s digester, they become soluble, butare completely altered in their constitution, do not coagulate, nor gelatinise.In acetic and mineral acids fibrine and gluten increase in bulk, and becometransparent and gelatinous. Extremely dilute aqueous solutions of causticpotassa and soda dissolve these substances, and acids precipitate thesesolutions.