4 777^ ULTIMATE CONSTITUENTS OF PLANTS 



a small hard-glass tube with a piece of bright metallic 

 sodium about the size of a pea. On the application of 

 heat a violent reaction results, after which the tempera- 

 ture should be raised to bright redness. 



The end of the tube while still hot is dipped into 

 a few CCS. of water contained in an evaporating 

 basin. The tube will crack, and the charred contents 

 are then boiled with the water for a few moments. 

 After filtering off the glass and carbonaceous particles, 

 a few drops of ferrous sulphate solution are added 

 to the filtrate, which is then acidified with a little 

 strong hydrochloric acid. On the further addition of 

 a small quantity of ferric chloride solution, the pro- 

 duction of a precipitate of Prussian blue will be indicative 

 of nitrogen in the substance originally taken. This 

 nitrogen combines with the metallic sodium and some 

 of the carbon under the action of heat to form sodium 

 cyanide, NaCN, which is converted into sodium ferro- 

 cyanide by the action of the ferrous sulphate. The 

 addition of the ferric chloride to the acid solution 

 results in the precipitation of ferric ferrocyanide, or 

 Prussian blue. 



The nitrogen present in plants and plant products is in com- 

 bination in the form of amines and amides, proteins, nitrates, 

 salts of ammonium, etc. 



2. Qualitative Detection of Phosphorus. 



{a) A little of the finely chopped or ground substance 

 is mixed with about its own weight of magnesium 

 powder, and heated strongly in a small hard-glass tube. 

 A slight explosion indicates that the magnesium has 

 decomposed the organic substance, and any phosphorus 

 present will have been converted into magnesium 

 phosphide, MggPg. After cooling, a single drop of 

 water is allowed to run on to the residue, whereby 



