336 PROTEIN-COMPOUNDS. 



Combinations. Albumen-protein contains, according to Mulder, 

 53'74- of carbon, 7'0 of hydrogen, 14'2 of nitrogen, 23- 5% of 

 oxygen, and 1 *6 of sulphur. He prepares it by dissolving pure 

 coagulated albumen in a solution containing from -r^th to T^th 

 of caustic potash, and exposing it for the space of an hour to a 

 temperature of from 60 to 80. The presence of sulphide of 

 potassium in the solution may then be proved by the ordinary 

 reagents. If we were at once to neutralise the fluid with acetic acid, 

 there would be a danger that the precipitate would contain an 

 admixture of sulphur, since, in 'addition to the sulphide of potas- 

 sium, the fluid must also contain hyposulphite of potash, which 

 on the addition of an acid, deposits sulphur, and forms sulphurous 

 acid ; this sulphurous acid again, as is well known, yields sulphur 

 with the sulphuretted hydrogen which is developed ; hence the 

 fluid must be exposed to the air, and at the same time frequently 

 stirred till it ceases to yield any further indication of the presence 

 of sulphide of potassium ; then, and not till then, we may precipi- 

 tate the desired body by acetic acid. 



When newly precipitated, albumen-protein is of a snow-white 

 colour, and in the form of minute flakes ; when dried, it assumes a 

 pale yellow tint, is hard and brittle, swells in water into a jelly, 

 but is insoluble in that fluid as well as in all indifferent menstrua, 

 and for the rest behaves like coagulated albumen, with this excep- 

 tion only, that after the treatment with potash, it yields no indi- 

 cation of the presence of sulphur, either with the salts of lead or 

 on silver foil. 



Preparation. We have already shown that soluble albumen 

 cannot be obtained perfectly free from mineral constituents. The 

 soluble modification may be obtained in the greatest purity by 

 neutralising serum or the white of egg dissolved in water with a little 

 acetic acid, arid extracting with from 20 to 30 times the quantity 

 of distilled water, or with dilute spirit. It is however usually 

 prepared by evaporating the serum of the blood, or the white of egg 

 in platinum vessels, either in vacua or at a temperature not ex- 

 ceeding 50, pulverising the yellow residue, and extracting it with 

 ether, and finally with alcohol. 



Coagulated albumen is obtained in a perfectly pure state by 

 washing the precipitate yielded on the addition of hydrochloric 

 acid to solutions of white of egg, with dilute hydrochloric acid, in 

 order to remove the salts, and especially the phosphate of lime; 

 by dissolving the hydrochlorate of albumen in pure water, and 

 precipitating it with carbonate of ammonia. The precipitate 



