PROTEINS. IO3 



solutions by saturation with solid sodium chloride or magnesium 

 sulphate. As a class they are much less stable than the albumins, 

 a fact shown by the increasing difficulty with which a globulin 

 dissolves during the course of successive reprecipitations. 



We have used an albumin of animal origin (egg albumin) for 

 all the protein tests thus far, whereas the globulin to be studied 

 will be prepared from a vegetable source. There being no essential 

 difference between animal and vegetable proteins, the vegetable 

 globulin we shall study may be taken as a true type of all globulins, 

 both animal and vegetable. 



EXPERIMENTS ON GLOBULIN. 



Preparation of the Globulin. Extract 20-30 grams (a hand- 

 ful) of crushed hemp seed with a. 5 per cent solution of sodium chlo- 

 ride for one-half hour at 60 C. Filter while hot through a paper 

 moistened with 5 per cent sodium chloride solution. Place the 

 filtrate in the water-bath at 60 C. and allow it to stand for 24 

 hours in order that the globulin may crystallize slowly. In case 

 the filtrate is cloudy is should be warmed to 60 C. in order to 

 produce a clear solution. The globulin is soluble in hot 5 per cent 

 sodium chloride solution and is thus extracted from the hemp seed, 

 but upon cooling this solution much of the globulin separates in 

 crystalline form. This particular globulin is called edestin. It 

 crystallizes in several different forms, chiefly octahedra (see Fig. 

 33, page 104). (The crystalline form of excelsin, a protein ob- 

 tained from the Brazil nut, is shown in Fig. 34, page 105. This 

 vegetable protein crystallizes in the form of hexagonal plates.) 

 Filter off the edestin and make the following tests on the crystalline 

 body and on the filtrate which still contains some of the extracted 

 globulin. 



TESTS ON CRYSTALLIZED EDESTIN. (i) Microscopical examina- 

 tion (see Fig. 33, p. 104). 



(2) Solubility. Try the solubility in the ordinary solvents (see 

 page 23). Keep these solubilities in mind for comparison with 

 those of edestan, to be made later (see page 109). 



(3) Milloris Reaction. 



(4) Coagulation Test. Place a small amount of the globulin in 

 a test-tube, add a little water and boil. Now add dilute hydrochloric 

 acid and note that the protein no longer dissolves. It has been 

 coagulated. 



