I.] THE PROTEIDS. 5 



varies considerably with a large number of conditions. When 

 dried at 40° C. they yield a clear yellow coloured mass, " soluble 

 albumin," which is soluble in water. 



(i.) Egg- Albumin. — Prepare a solution (Lesson I. 1.). 



{a. ) Evaporate some of the fluid to dryness at 40° C. over a water-bath to 

 obtain "soluble albumin." Study its characters, notably its solubility in 

 water. This solution gives all the tests of egg-albumin. It is more con- 

 venient to purchase this substance. 



{}).) The fluid gives all the general proteid reactions. 



{rj) Precipitate portions of the fluid with strong mineral acids, 

 including sulphuric and hydrochloric acids. 



{d.) Precipitate other portions by each of the following : — Mer- 

 curic chloride, basic lead acetate, tannic acid, alcohol, picric acid. 



(e.) Take 5 cc. of the fluid, add twice its volume of o.i per cent, 

 sulphuric acid, and then add ether. Shake briskly = coagulation 

 after a time, at the line of junction of the fluids. 



(/.) The solution is 7iot precipitated on saturation with crystals 

 of sodic chloride or magnesic sulphate, but it is completely pre- 

 cipitated on saturation with ammonium sulphate (NHJ^80^ (com- 

 pare " Globulins "). 



{g.) A solution containing 1-3 per cent, of salts coagulates at 

 about 56° C. 



(2.) Serum-Albumin. — Blood-serum (see "Blood") contains 

 serum-albumin and serum- globulin. Dilute blood-serum until it 

 has the same specific gravity as the egg-albumin solution. A shglit 

 opalescence, due to precipitation of serum-globulin, is obtained. 

 Neutralise the solution with very dilute acid until a faint haziness 

 is obtained. 



Eepeat the tests for egg-albumin, and, in addition, with undiluted 

 blood-serum. 



(/?.) Add crystals of MgSO^ to saturation, shaking the flask 

 vigorously to do so = a white precipitate of serum-globulin. Filter. 

 The filtrate contains serum-albumin. 



{i.) Saturate serum with (]SrH^)^S04 = white precipitate of both 

 serum-albumin and serum-globulin. Filter. The filtrate contains 

 no proteids. 



EGG-ALBUMIN. SERUM-ALBUMIN. 



(i.) Readily precipitated by (i.) It is also precipitated by 



hydrochloric acid, but the pre- hydrochloric acid, but not so 



cipitate is not readily soluble in readily, while the precipitate is 



excess. soluble in excess. 



(ii.) A non-alkahne solution (ii.) It is not coagulated by 



is coagulated by ether. ether. 



