180 CHEMISTRY. 



is another case of allotropism, which, you remember, in the 

 case of ozone and carbon was attributed to a difference in 

 the arrangement of the atoms. 



252. Lucifer-Matches. As phosphorus can be ignited by 

 friction, it is used in the manufacture of hicifer-matches. 

 The substance on the ends of the matches is a mixture of 

 phosphorus with other substances that contain considerable 

 oxygen, the composition being done up in mucilage of gum 

 arabic. The object is to supply oxygen in the immediate 

 neighborhood of the phosphorus, that the friction may read- 

 ily produce combustion. The particles of the phosphorus 

 are so much shut in from the air in the dried mass that the 

 oxygen of the air can get admission to comparatively a 

 small portion of them. The substances containing oxygen 

 that are commonly used are red-lead (oxide of lead), potas- 

 sium nitrate, and potassium chlorate. A formula given by 

 Stockhardt is this: If parts of phosphorus, 4 each of gum- 

 arabic and water, 2 of nitre, and 2 of red -lead. Safety 

 matches are made with amorphous phosphorus, which is 

 less liable to be set on fire by accidental friction. Some- 

 times the phosphorus composition is applied only to the 

 surface of the box, and then the matches ignite only when 

 rubbed on this surface. 



253. Mode of Obtaining Phosphorus. As already stated, 

 phosphorus is obtained from bones. These are composed 

 mostly of an animal substance, gelatine, and a mineral sub- 

 stance, phosphate of lime. The gelatine is first burned out, 

 and the phosphate of lime which is left is reduced to pow- 

 der. This powder is digested with dilute sulphuric acid, 

 and in consequence a sulphate of lime is formed, which is 

 an insoluble substance. As, therefore, phosphate of lime is 

 composed of phosphoric acid and lime, the lime being re- 

 moved, we have the phosphoric acid dissolved in the dilute 

 sulphuric acid. This solution, after being strained, is mixed 



