ix SULPHUR AND PHOSPHORUS 179 



combustion; but that the same air then diminishes con- 

 siderably in volume, until, when the vessels are cold, it only 

 occupies four-fifths or five-sixths of the space which it 

 occupied before the combustion. If the flowers or white 

 flakes, which are found during this operation, are collected 

 and weighed before they have come into contact with fresh 

 air, and without allowing them to absorb moisture, one 

 observes that they are two and a half times as heavy as the 

 phosphorus used to produce them, in other words, that 

 from a grain of phosphorus 2\ grains of solid phosphoric 

 acid have been produced." 



" The air which has thus been diminished as much as 

 possible by the combustion of phosphorus, is not denser 

 than atmospheric air ; its specific weight is even diminished 

 rather than increased ; it is no longer fit for the respiration 

 of animals nor for the combustion, nor inflammation of 

 substances" {Works, II. 139-140). 



Phosphoric acid and the phosphates. The white solid 

 prepared by burning phosphorus in air is now called 

 PHOSPHORIC ANHYDRIDE, the name PHOSPHORIC ACID being 

 reserved for the product obtained by the action of water 

 upon it. Lavoisier showed that phosphoric acid could be 

 prepared by the action of warm nitric acid upon phosphorus 

 (Works^ II. 277), as well as by burning it in air. He also 

 prepared a number of salts of phosphoric acid, and 

 described them as PHOSPHATES. 



Phosphorous acid and the phosphites. A different acid is 

 produced when phosphprus is allowed to smoulder, e.g. by 

 putting small pieces of phosphorus on the sloping sides of a 

 glass funnel, and letting the liquid drop into a bottle as 

 it is formed. The acid was examined by Sage (Mem. Acad. 

 Set., 1777, 91, 435). He found that the salts prepared by 

 neutralising it with soda or potash, unlike those prepared by 

 Lavoisier from burnt phosphorus, were not deliquescent, i.e. 

 did not become liquid by absorbing moisture from the 

 air. Gengembre noticed that the freshly-prepared acid 

 " is still luminous in the dark, and retains a slight odour of 



N 2 



