Dissolved in glacial acetic acid and treated with concentrated sulphuric acid, albumins and peptones give a violet and feebly fluorescent solution. A somewhat similar reaction is obtained if sugar solution be substituted for acetic acid. A solution of albumin rendered strongly acid with acetic acid is precipitated by potassium ferrocyanide, salt, sodium sulphate, lead acetate, mercuric chloride, tannin and picric and tungstic acids. _Egg-Albumin_ is contained in the whites of eggs in membranes which are broken up by beating with water and can then be removed by filtration. When fresh its reaction is slightly alkaline, and it is lævorotatory. According to Lehmann, white of egg contains 87 per cent. of water, and 13 per cent. of solid matter, the latter being almost entirely composed of egg-albumin. This latter coagulates and becomes insoluble in water on heating to 60° C. _Vitellin_ (the albumin or globulin[48] of the yolk) is insoluble in water, and is obtained as a white granular residue on extracting undried egg-yolk with large quantities of ether. It closely resembles myosin, the chief globulin of muscle, but differs from other globulins in being soluble in a saturated solution of common salt. A neutral solution of vitellin in very dilute brine coagulates at 70-75° C. [48] Globulin is an albumin soluble in dilute salt solutions, but insoluble in water. Yolks of eggs, preserved by the addition of salt, borax, or formalin, are used for dressing skins in the process of “tawing” (see p. 191). For the analysis of such yolks, see L.I.L.B., p. 159. Their most important constituent for the leather-dresser is egg-oil of which they contain about 30 per cent. _Casein_, the principal proteid of milk, may be mentioned here in connection with the albumins to which it is closely related, since, though in no way connected with the animal skin, since it is used to some extent as a “seasoning” or glaze for leather, for which it is well adapted, and it is now to a considerable extent a waste product of butter manufacture. It differs from albumins in being very incompletely if at all coagulated by boiling, but separates at once in curdy flakes on the addition of acids (hydrochloric, acetic, butyric), and by the action of rennet. The curd is easily soluble in small quantities of dilute alkalies, lime-water, and salts of alkaline reaction, such as sodium carbonate and borax. If no more than the necessary quantity of alkali is employed for solution, the compound has an acid reaction to phenolphthalein, and like the original milk, is curdled by rennet and dilute acids. Casein may also be dissolved by digestion with diluted mineral or organic acids.