SULPHUR AND PHOSPHORUS. 361 



they form together a solid crystalline hydrate j which when 

 thrown into water gives off nitrous, and forms a solution of 

 sulphuric acid. 



I have referred, in the Philosophical Transactions, to the chlorine and 

 combination of chlorine and sulphur. I have been able to form sulphur. 

 no compound of these bodies, which does not deposit sulphur 

 by the action of water. When sulphur is satured with chlo- 

 rine, as in Dr, Thomson's sulphuretted liquor, it appears to 

 contain, from my experiments, only 6^ of chlorine to 30 of 

 sulphur. 



4. Some general Observations. 



It is a fact worthy of notice, that phosphoric and sulphuric Observations, 

 acids should contain the same quantity of oxygen to the same tions^in°phos- 

 quantity jof inflammable matter; and yet that the oxygen phoric and 

 should be combined in them, with such different degrees of ^"Selamef 

 affinity. Phosphorous acid has a great tendency to unite witti though the 

 oxygen, and absorbs it even from water : and sulphureous ^"^^j"' j"^gp 

 acid can only retain it when water is present. 



The relation of water to the composition of many bodies has Most precipi- 

 already occupied the attention of some distinguished chemists, ^vater contain 

 and is well worthy of being further studied ; most of the sub- that ingrc- 

 stances obtained by precipitation from aqueous solutions are, 1 '^'''^"** 

 find, compounds of water. 



Thus zircona, magnesia, silica, when precipitated and dried 

 at 212** still contain definite proportions of water. And many 

 of the substances which have been considered as metallic 

 oxides, that I have examined, obtained from solutions, agree 

 in this respect j and their colours and other properties are mate- 

 rially influenced by this combined water. 



I shall give an instance. The substance which has been called Instance, 

 the white oxide of manganese is a compound of water and the 

 protoxide of manganese, and when heated strongly, it gives 

 off its water and becomes a dark olive oxide. 



It has been often suspected, that the contraction of volume Contraction 



produced in the pure earths by heat, is owing to the expulsion eLths b^heat 



of water combined with them. The following fact seems to arises from the 



confirm this suspicion, and offers a curious phenomenon. expulsion of 



^ ' r water. 



Zircona, precipitated from its solution in muriatic acid by an 



alkali. 



