PROPERTIES OF THE PROTEINS. 33 



or on a wire. Notice that it turns black from the presence 

 of carbon. Observe the characteristic odor. On continued 

 heating it will all disappear except the mineral matters, 

 or ash. 



72. Mix a few fragments of dry albumin with an 

 excess of powdered soda-lime and heat the mixture in a 

 dry test-tube. Test the vapors which escape for ammonia, 

 both by the odor and by their action, on a piece of red lit- 

 mus-paper. The ammonia proves that the albumin con- 

 tained nitrogen. 



73. Make a solution of lead hydrate by adding so- 

 dium hydrate to a small amount of lead acetate solution 

 until the precipitate first formed has dissolved. Add to it 

 a protein compound, like albumin, and boil. The presence 

 of sulphur (cystein sulphur) in the protein compound is 

 shown by the dark-colored lead sulphid, which it forms by 

 uniting with the lead. 



74. Very small quantities of sulphur maybe shown by chang- 

 ing it to a sulphid and testing for the latter with sodium nitro- 

 prussid. By this means it can be found in a single hair. Shut off 

 the air from a Bunsen burner and, after turning it low, cover the 

 hair with sodium carbonate and hold it on a wire in the middle of 

 the flame. Allow the substance to fuse, being careful to keep it in 

 the yellow flame to prevent oxidation. Then dissolve the mass in 

 a few drops of water in a porcelain dish. Add to the solution a 

 very small crystal of sodium nitroprussid. The presence of sul- 

 phid is shown by the production of a purple or violet color, which 

 is destroyed by an excess of the nitroprussid. 



75. Test a solution of egg-albumin or any other albuminous 

 substance to see if it will pass through a dialyzer. Only the pep- 

 tones will pass through the membrane. The biuret test can be 

 used to detect them (Experiment 76). 



