PROTEINS 107 



Calculate the exact volume of acid necessary to precipitate the remaining portion 

 of the original albumin mixture and add this calculated quantity. Mix the two 

 portions of albumin and allow to stand over night. Remove a drop of the suspended 

 material to a slide and examine microscopically. Crystals in the form of fine 

 needles will be observed. This is the crystallized egg albumin. To recrystallize, 

 filter off the crystals and dissolve them in the smallest possible volume of water. 

 Filter, and to the filtrate carefully add saturated ammonium sulphate until a faint, 

 permanent precipitate is formed. Allow the mixture to stand several hours and 

 examine as before. The crystals of albumin should be somewhat larger than when 

 first examined. 



The above method may also be used for crystallizing serum albumin from the 

 fresh blood serum of the horse, mule or ass. 



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 

 4 volumes of water and filtered. The filtrate is evaporated on a water-bath at 

 about 5oC. and the residue powdered in a mortar. 



1 6. Tests on Powdered Egg Albumin. With powdered albumin prepared as 

 described above (by yourself or furnished by the instructor), try the following 

 tests : 



(a) Solubility . Test the solubility of the albumin in water, sodium chloride, 

 dilute acid and alkali. 



(b) Millon's Reaction. 



(c) Glyoxylic Acid Reaction (Hopkins-Cole). 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 dry powder in a dry 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 lead acetate 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 pres- 

 ence of nitrogen and hydrogen ; the lead 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. Moisture indicates hydrogen only in case 

 both powder and test-tube used in the test are absolutely dry. 



(e) Coagulation Test. 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 (a) above. It is still 

 soluble. Why has it not been coagulated? Repeat the above experiments 

 with powdered serum albumin and see how the results compare with those 

 just obtained. 



SULPHUR IN PROTEIN 



Sulphur is believed to be present in two different forms in the pro- 

 tein molecule. The first form, which is present in greatest amount, 



