178 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



earthenware retort, and distilled by a strong red heat, when 

 the phosphorus comes over, and is received in the water 

 into which the tube of the retort is immersed " (New System, 

 1810, II. 240-241). 



Properties of phosphorus. Phosphorus is a wax-like 

 solid, which melts about blood-heat, and is so extremely 

 inflammable that it must be preserved under water. When 

 exposed to the air it undergoes a slow combustion, and 

 exhibits the luminosity from which it derives its name. 

 When gently heated it takes fire and burns very vigorously, 

 emitting white fumes. 



The burning of phosphorus. The burning of phosphorus 

 was investigated in 1772 by Lavoisier, who showed that it 

 gained in weight, in just the same way as sulphur and the 

 metals. 



His observations are described in a " Memoir on the 

 Combustion of Phosphorus and on the nature of the acid 

 which results from this combustion " (Mew.. Acad. Sri., 1777, 

 p. 65 ; Works, II. 139), as follows : 



" If phosphorus is ignited, by means of a burning-glass, 

 under a bell-jar immersed in mercury, one observes : 



(1) That only a given quantity of phosphorus can be 

 burned in a given quantity of air, and that this quantity is 

 about i grain for 1 6 to 1 8 cubic inches of air. 



(2) That, when this quantity has been burnt, the phos- 

 phorus is extinguished, and cannot be relighted, unless 

 brought into contact with a quantity of fresh air, which has 

 not been used for combustion. 



(3) That fresh phosphorus, introduced under the same 

 bell-jar, burns no better than the first. 



(4) That, during the burning of the phosphorus, there is 

 formed a great abundance of white flowers or flakes, like 

 very fine snow, which attach themselves everywhere to the 

 interior of the bell-jar, and are nothing else than solid 

 phosphoric acid. 



(5) That, at the first moment of combustion, the air in 

 the jar expands considerably, on account of the heat of the 



