HYDROGEN AND SULPHUR. 401 



for instance, by SiF 2 -f-KF; and the hydrofluosilicic acid of 

 Berzelius, by Si F 2 + II F. Dr. Clark connects with this an in- 

 teresting speculation respecting the constitution of these salts, 

 which he would assimilate to the ferrocyanide of potassium, 

 considered as a compound of ferrocyanogen and potassium, 

 Cy 3 Fe + 2K. The fluoride of silicon and potassium may be viewed 

 in the same way, as a compound of a salt-radical containing the 

 silicon and all the fluorine of the salt, with potassium ; that is, 

 Si F 3 -fK ; a view which accounts for some salts of this class not 

 being decomposed by potash, and which is favoured by the in- 

 creasing number of classes of salts, which appear to be formed 

 on a similar type. 



No combination of fluorine with oxygen is known, nor of 

 fluorine with nitrogen or carbon. 



Fluorides of sulphur and of phosphorus were formed by Davy, 

 by distilling the fluoride of lead or of mercury with sulphur or 

 phosphorus, in platinum vessels. There result a sulphuret or 

 phosphuret of the metal, and a fluoride of sulphur or of phos- 

 phorus, which volatilizes. Both of these compounds present 

 themselves as fuming liquids. The fluoride of phosphorus is de- 

 composed by water, hydrofluoric acid with phosphorous acid 

 being formed ; it is, therefore, a terfluoride of phosphorus, P F 3 . 

 This fluoride is capable of taking fire and burning in air, when 

 it is presumed that phosphoric acid is produced, and gaseous 

 fluorine set free, which diffuses itself in the atmosphere. 



CHAPTER II. 



COMPOUNDS OF HYDROGEN. 



SECTION I. 

 HYDROGEN AND SULPHUR, 



SULPHURETTED HYDROGEN, or HYDROSULPHURIC ACID ; 

 %. 213.67 or 17.12; SH; density 117 7; [~T~I- 



Certain compounds of hydrogen with the non-metallic ele- 

 ments have been reserved for separate consideration, which 

 could not be introduced with advantage at an earlier period : 



D D 



