ALBUMINOUS COMPOUNDS. 109 



blue ; after standing for some time, it again assumes its former pink or 

 claret colour. In the precipitation of Albumen by an acid, definite 

 compounds are formed between the two ; in which the Albumen acts the 

 part of a base. On the other hand, it serves as an acid in its combina- 

 tions with the caustic alkalies, and is held in solution by them. Most 

 of the metallic salts, as those of Copper, Lead, Mercury, &c., form 

 insoluble compounds with albumen, and thus give precipitates with its 

 solution ; hence the value of white of egg as an antidote, in cases of 

 poisoning with Corrosive Sublimate. The simplest method of detecting 

 the presence of soluble Albumen in very small quantity, is to boil the 

 liquid, and add nitric acid ; if turbidity is then produced, the existence 

 of albumen may be inferred. A more delicate test of the presence of 

 Albumen, however, is the precipitate which is given by the addition of 

 the ferro-prussiate of potash to the liquid, when this has been first 

 acidulated with acetic acid. 



170. Albumen is readily decomposed by the action of the fixed alka- 

 lies ; a disengagement of ammonia being occasioned by the addition of 

 caustic potass to even a very weak solution of albumen. This may be 

 made evident by adding a solution of sulphate of copper, a deep purple 

 colour being produced by the action of the liberated ammonia upon the 

 metal ; and thus the addition of liquor potassse and a solution of sul- 

 phate of copper, forms a very delicate test for the presence of albumen. 

 If Albumen, or any albuminous compound, be heated with caustic 

 potash, it is completely decomposed ; not, however, being resolved at 

 once into its ultimate constituents, or altogether into simple combina- 

 tions of them, but in great part into other organic compounds. One of 

 these, termed Leucin, is a crystalline substance, which forms colourless 

 scales, destitute of taste and odour ; it is soluble in water and alcohol, 

 and sublimes unchanged. It consists of 12 Carbon, 12 Hydrogen, 1 

 Nitrogen, and 4 Oxygen. There is not at present any evidence that it 

 is produced in the living body ; and the chief interest which attaches to 

 it arises from the fact, that it may be procured from Gelatine as well 

 as from Proteine ; which indicates a certain relationship between these 

 two substances. Another compound obtained by the same reaction, is 

 called Tyrosin ; it crystallizes in brilliant needles; and its composition 

 is 16 C, 9 H, 1 N, 5 0. Besides these substances, Ammonia, with 

 Formic and Carbonic Acids, are produced; the acids unite with the 

 potash employed to effect the decomposition ; and the ammonia is set 

 The action of caustic potash upon Albumen has also the effect 

 of liberating sulphur, which unites with the potash, and remains in the 

 solution, where its presence may be recognised by the black precipitate 

 formed on the addition of a solution of acetate of lead. The existence 

 of unoxidized Sulphur in albumen is shown by the familiar fact of the 

 blackening of a silver spoon by a boiled egg, which is due to the forma- 

 tion of an alkaline sulphuret during coagulation. Albumen may also 

 be shown to contain Phosphorus in an unoxidized state. In its soluble 

 state, Albumen is very commonly united with Phosphate of Lime, about 

 two per cent, of which may be taken up by it ; and it is chiefly in this 

 mode, that this very important substance is introduced into the Animal 

 body. 



