ix SULPHUR AND PHOSPHORUS 177 



an attribute which belongs only to oxygen, I will only add 

 that sulphuretted hydrogen contains no oxygen, and that it 

 differs very little, in its acid properties, from carbonic acid, 

 which contains nearly 76 per cent, of oxygen " (loc. at., 

 237-238) 



Sulphides and polysulphides. Whilst artificial sulphide of 

 iron is converted by oil of vitriol into sulphuretted hydrogen 

 and sulphate of iron, iron pyrites is found to liberate sulphur 

 as an additional product. Sulphides of this kind, which 

 liberate sulphur when acted on by acids, are distinguished as 

 POLYSULPHIDES. The preparation of " milk of sulphur " 

 from " liver of sulphur " by the action of acids depends in 

 part on the fact that soluble polysulphides are formed when 

 sulphur is dissolved in an alkali. 



C. PHOSPHORUS. 



The preparation of phosphorus. The inflammable 

 element PHOSPHORUS was prepared during the i7th 

 and 1 8th centuries, by a number of chemists, including 

 Brand, Kunkel, and Robert Boyle, by evaporating urine to 

 dryness, mixing it with sand, and heating strongly. It was 

 afterwards prepared from bones. 1 Dalton describes the 

 process as follows : 



" Phosphorus is usually prepared from the bones 



of animals, which contain one of its compounds, phosphate 

 of lime, by a laborious and complex process. The bones 

 are calcined in an open fire; when reduced to powder, 

 sulphuric acid diluted with water is added ; this acid takes 

 part of the lime, and forms an insoluble compound, but 

 detaches superphosphate of lime, which is soluble in water. 

 This solution is evaporated, and the salt obtained is in a 

 glacial state. The solid is reduced to powder, and mixed with 

 half its weight of charcoal ; then the mixture is put into an 



1 A full description of the method is given by Pelletier, Journal dc 

 Physique, 1785, 27, 26-32. 



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