CHAPTER XX 



PHOSPHORUS AND ITS COMPOUNDS 



General Characters of Phosphorus. Phosphorus, like sul- 

 phur, exists in different allotropic forms, and these must be first 

 examined. Ordinary phosphorus, which is always kept under 

 water, will probably appear at first to be a yellow, or brown, 

 opaque solid. This is not, however, its true appearance, but 

 only that of a film which coats the exterior. If a piece be cut 

 it will be found to consist of a waxy, translucent solid, of a 

 pale yellow colour. It very readily inflames, contact with any 

 warm object being sufficient to start the combustion. For this 

 reason it should not be handled, and when not in use should be 

 kept immersed in water, in which it is insoluble. Phosphorus 

 glows in the dark, forming white fumes. Both glow and fumes 

 are due to its gradual oxidation. Phosphorus itself, as well as 

 the fumes of its oxide, is poisonous, and hence care must be 

 taken during its use, both on this account and on account of its 

 inflammability. 



EXPT. 286. Place a little phosphorus in an evaporating basin 

 containing water and heat slowly. Observe the temperature 

 at which the phosphorus is seen to melt. Allow it to cool. 



You will find that the phosphorus melts at about 43' C., but 

 remains liquid below this temperature. This is frequently the 

 case with melted solids, but during the solidification the tem- 

 perature again rises to the melting point. If the water be 

 poured off", the phosphorus frequently catches fire, as it inflames 

 in air at a temperature below the melting point. 



EXPT. 287. Shake up a small piece of phosphorus in 

 carbon disulphide. Observe that it dissolves. Pour the solu- 

 tion on to a piece of filter paper. Observe the effect. 



