PROTEINS. 10 1 



drop of 0.2 per cent hydrochloric acid, to the second one drop 

 of potassium hydroxide solution and leave the third neutral in reac- 

 tion. Add to each tube a few drops of egg albumin solution and 

 note the results. What do you conclude from this experiment? 

 Alcohol precipitates proteins unaltered but if allowed to remain 

 under alcohol the protein is transformed. The " fixing" of tissues 

 for histological examination by means of alcohol is an illustra- 

 tion of the application of this transformation produced by alcohol. 

 It apparently is a process of dehydrolysis. 



15. Preparation of Powdered Egg Albumin. This may be 

 prepared as follows : Ordinary egg-white finely divided by means 

 of scissors or a beater is treated with four volumes of water and 

 filtered. The filtrate is evaporated on a water-bath at about 50 C. 

 and the residue powdered in a mortar. 



1 6. Tests on Powdered Egg Albumin. With powdered albu- 

 min prepared as described above (by yourself or furnished by the 

 instructor), try the following tests: 



(a) Solubility. 



(b) Millon's Reaction. 



(c) Hopkins-Cole Reaction. When used to detect the presence 

 of protein in solid form this reaction should be conducted as follows : 

 Place 5 c.c. of concentrated sulphuric acid in a test-tube and add 

 carefully, by means of a pipette, 3-5 c.c. of Hopkins-Cole reagent. 

 Introduce a small amount of the solid substance to be tested, 

 agitate the tube slightly, and note that the suspended pieces assume 

 a reddish-violet color, which is the characteristic end-reaction of 

 the Hopkins-Cole test; later the solution will also assume the 

 reddish-violet color. 



(d) Composition Test. Heat some of the powder in a test- 

 tube in which is suspended a strip of moistened red litmus paper 

 and across the mouth of which is placed a piece of filter paper 

 moistened with plumbic acetic solution. As the powder is heated 

 it chars, indicating the presence of carbon; the fumes of ammonia 

 are evolved, turning the red litmus paper blue and indicating the 

 presence of nitrogen and hydrogen; the plumbic acetate paper is 

 blackened, indicating the presence of sulphur, and the deposition 

 of moisture on the side of the tube indicates the presence of 

 hydrogen. 



(e) Immerse a dry test-tube containing a little powdered egg 

 albumin in boiling water for a few moments. Remove and test 

 the solubility of the albumin according to the directions given under 



