36 ALBUMEN. [CHAP. I. 



Albumen may be readily made to pass from the fluid to the solid 

 state, or to coagulate, by the influence of certain reagents; but it 

 has no spontaneous tendency to assume the solid form, except by 

 the loss of the water which is combined with it. By evaporating 

 white of eggs, at a temperature not exceeding 120, its water is 

 driven off, and solid albumen, in the form of a yellowish transparent 

 brittle mass, is obtained with all its properties unimpaired. If a 

 solution of albumen, as serum of the blood, be exposed to a heat 

 between 140 and 150, it coagulates, and then it becomes in- 

 soluble in water. 



The mineral acids have the property of coagulating albumen. 

 Of these, that which is most used in medical practice is the nitric, a 

 drop or two of which will readily detect a small quantity of albu- 

 men dissolved in a clear fluid, by rendering it more or less opaque. 

 Alcohol also has this property ; and hence any albuminous textures 

 submitted to its influence become hardened and condensed. Bi- 

 chloride of mercury exercises a similar influence, and is a delicate 

 test for albumen. It was Orfila who first employed this proximate 

 principle as an antidote to the poisonous effects of the bichloride, 

 which combines with the albumen and is by it partially converted 

 into calomel. According to Peschier, the white of one egg is 

 sufficient to render four grains of the poison innocuous. 



Another delicate test for albumen is the ferro-cyanide of potas- 

 sium, which will precipitate it from solution, provided a little acetic 

 acid have been previously added, in order to neutralise the soda in 

 combination with it. Albumen is also precipitated from solution 

 by tannin. 



Albumen coagulates at the negative pole of the galvanic battery, 

 or at both poles, when a strong battery is employed. 



Many other reagents will coagulate this principle, but enough 

 have been mentioned for all practical purposes. 



It often happens that albumen is carried off from the system in 

 large quantities by the urine. By any of the means above-mentioned, 

 its presence in that fluid may be detected. When heat is used, 

 it will always be advisable to ascertain previously whether the urine 

 be acid or alkaline ; for the presence of alkali prevents the coagula- 

 tion of albumen by heat. Hence it is a good rule, in testing for 

 this substance, to employ both heat and nitric acid. 



Albumen is soluble in caustic alkalies. 



The existence of sulphur as a constituent of albumen, is shewn 

 by the blackening of silver that has remained long in contact 

 with it. 



