70 



Possibly these nitrogenous substances might be classed by them- 

 selves as colloids. They are possibly less hydrous than the proteids or 

 albumenoids. This table exhibits their per centage composition. 



C. H. N. S. O. 



Hair 49.7 6.4 17.1 5.0 21.8 



Wool 50.6 7.0 17.7 ? 



Feathers 51.9 7.2 17.S ? 



Skin (humansole) 503 6.8 17.2 ? 



Oxhorn 50.7 6.7 16.2 ? 



Glue 50.0 6.5 17.5 ? 



Gelatine 50.0 6.7 18.3 ? 



Formulae of the Colloids. 



Gelatine 102.0 151. ^1. 39 



Chondrine 99.0 156. 40. 42 



Keratine 2 3-5 381- 70. 6. 77 



We learn from the characters of the colloids that some nitrogenous 

 substances are very stable. Such are the compounds which constitute 

 the horns and hoofs of animals, the latter constituting the raw 

 materials for the manufacture of those important products used in the 

 arts and called cyanides, ferrocyanides, sulphocyanides, &c. The first 

 step in their production is the fusion of the substances rich in nitrogen 

 with carbonate of potassa in iron vessels. Subsequent lixivation and 

 crystallisation yield what was long known as yellow Prussiate. The 

 essential constituent of these salts is the compound radical Cyanogen 

 C-i N._, as it is also of the well-known pigment called Prussian Blue. In 

 fact the history of these compounds begins with the production 

 of Prussian Blue about 180 years ago. Equal parts of cream 

 of Tartar, saltpetre and and ox-blood were heated together in order to 

 produce the solution from which, by the use of green vitriol, the colour 

 was precipitated. 



Experiments. Production of Prussian Blue. Decomposition of 

 mercuric sulphocyanide. 



Another very interesting set of nitrogenous substances are those 

 which are formed in dead and decomposing animal matter. These are 

 sometimes of a basic nature, ate formed in the human corpse after 



