1 62 CHEMISTRY FOR AGRICULTURAL STUDENTS 



produced. Try the experiment, and observe whether ammonia 

 is evolved. 



Among other nitrogenous organic compounds should be mentioned 

 cyanogen, CN, an organic radicle resembling in many respects chlorine. 

 Thus it forms hydrocyanic acid (prussic acid), HCN, like hydrochloric 

 acid, and cyanide of potassium, KCN, like chloride of potassium, etc. 

 These cyanides have a great tendency to form double salts. Among the 

 most important of these is ferrocyanide of potassium ("yellow prussiate of 

 potash "), K4Fe(CN)e. When treated with a solution of ferric chloride, this 

 yields ferric ferrocyanide, the well-known pigment " prussian blue." It 

 forms, therefore, a very delicate test for iron. If the ferrocyanide of 

 potassium be warmed with dilute sulphuric acid, hydrocyanic acid will 

 be set free, and if smelt cautiously (it is intensely poisonous) will serve to 

 illustrate the characteristic odour of oil of bitter almonds possessed by this 

 acid. 



XXXV. THE ALBUMINOIDS 



The albuminoids, as their name implies, resemble albumin or 

 white of egg in general properties. Their constitution is not 

 fully known, and they possess a somewhat indefinite com- 

 position, but all contain 50 to 55% carbon, 6.9 ta 7.5% 

 hydrogen, 20 to 24% oxygen, 15 to 18% nitrogen, and (pos- 

 sibly with some exceptions) .3 to 2% sulphur. Dry some white 

 of egg over a water bath, mix it with soda lime, and heat 

 strongly in a test-tube. Note that ammonia is given off, show- 

 ing that the albuminoid is a nitrogen compound. Empty the 

 solid residue into a beaker, and add excess of dilute sulphuric 

 acid. Note that sulphuretted hydrogen, recognised by its 

 smell and by the black stain of sulphide of lead it produces on 

 paper soaked in a solution of lead acetate, is evolved, showing 

 that sulphur also is a constituent of the albuminoid. 

 The albuminoids have not yet been synthetically prepared in 



