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i8 CHEMISTRY FOR AGRICULTURAL STUDENTS 



a similar kind, and an experiment on combustion should now 



be made. 



Cut under water a piece of phosphorus the size of a large 

 pea, and after drying it by means of blotting paper (taking care 

 not' to touch it with the fingers on account of its inflamma- 

 bility), place it on a capsule floating in a trough of water, and 

 ignite it. Place over the capsule an open bell 

 jar, and quickly close it with a stopper. Note 

 whether, in this case also, only a portion of 

 the air is consumed, and whether in proportion 

 it is approximately equal to that absorbed by 

 the iron filings. Does the residual gas support 

 the combustion of a taper ? Observe the fumes 

 of a white solid substance, which may be 

 supposed to be to phosphorus what iron rust is 

 TT""""*^ to iron, i.e. the product of the absorption of the 

 active constituent of the air. Observe also that 

 these fumes slowly dissolve in the water and render it acid, 

 this being shown not only by its taste, but also by its power 

 of changing the colour of a solution of litmus from blue to red, 

 a characteristic property of acid liquids. 



It will be noticed that the products of the rusting of iron 

 and the burning of phosphorus are entirely diff'erent in pro- 

 perties from the iron, the phosphorus, and the gas of which 

 they are composed. Iron rust is red in colour and devoid of 

 metallic lustre, and will be found to be, unlike iron, not 

 attracted by a magnet. The fumes from burning phosphorus 

 are not inflammable and are soluble in water, forming an acid 

 liquid. Nor has either substance any of the properties of the 

 gaseous constituent that has been absorbed. It is obvious that 

 the two constituents of each product have become united or 

 combined together so intimately that the characteristic pro- 

 perties of each constituent have been entirely changed, the 

 compounds having none of the properties that a mere mixture 

 would possess. 



