Metals. 233 



sulphuret, a carburet of the metal. Hydrogen 

 enters into similar combinations only with ar- 

 senic and tellurium. 



Sulphur is the most remarkable among the 

 combustibles for its effects on metals, which 

 show different degrees of attraction for it. Thus, 

 if to a compound of lead and sulphur we add 

 iron, and melt them, the iron unites with the 

 sulphur, and rises upwards with it, whilst the 

 lead is collected into a button at the bottom. A 

 compound of sulphur and fixed alkali proves in 

 general more powerful over the metals than the 

 sulphur or alkali by itself. 



Of salts, the acids have the greatest effect in 

 mixture upon metals, which have an attraction 

 for acids, and unite with them into compound 

 salts, many of which crystallize. The corro- 

 siveness of the acid is abated by its union with 

 the metal ; but not so much as in compounds 

 which contain alkaline salts or earths. There is 

 also a point of saturation : a given quantity of 

 acid converts only a given quantity of the metal 

 into a compound salt; and, on the contrary, 

 the metal attracts only a certain quantity of the 

 acid. But this saturation is not so invariable as 

 that of acids with absorbent earths* In many 

 cases the same quantity of metallic matter may 

 be united with different proportions of acids, and 

 the compound differs in appearance according 

 to the quantity of acid it contains. With a 

 iarge quantity of acid it is more soluble in water, 



