GENERAL OBSERVATIONS. 435 



heat alone at a temperature more or less elevated ; these metals 

 do not decompose water in any circumstances. They are mer- 

 cury, silver, palladium, platinum, gold, and probably rhodium 

 and iridium*. It is to be remarked of nearly all the metals 

 which decompose the vapour of water, and consequently sepa- 

 rate hydrogen from oxygen at a certain temperature, that their 

 oxides are reduced, notwithstanding, with great facility by hydro- 

 gen gas, and within the same limits of temperature. This ano- 

 malous result has already been adverted to in regard to iron 

 (p. 188). 



Of the thirteen non-metallic elements, hydrogen only forms 

 a basic oxide capable of uniting with acids. It is a general 

 character of the metals, on the contrary, to form such oxides, 

 if tellurium be excepted, which is more analogous in its chemical 

 properties to sulphur than to the metals. Hence, as the former 

 class are principally salt -radicals, the latter are principally 

 basyles. 



The protoxides of metals are uniformly and strongly basic, 

 but this feature becomes less distinct in their superior oxides, 

 and passes into the acid character in the high degrees of oxida- 

 tion of which some metals are susceptible. Thus, of manga- 

 nese, the protoxide is a strong base, the deutoxide basic but 

 in a less degree than the protoxide ; the peroxide indifferent, 

 and the still higher oxides are the manganic and hypermanga- 

 nic acids, which are respectively isomorphous with sulphuric 

 and hyperchloric acids. A few metals which have no protox- 

 ides, such as arsenic and antimony, are most remarkable for the 

 acids they form with oxygen, and thus more resemble in their 

 chemical history the elements of the non-metallic class. It is 

 indeed impossible to draw an exact line of demarcation between 

 the two classes of elements, either with reference to their physi- 

 cal or chemical properties. 



Besides combining with oxygen, metals combine with sul- 

 phur, chlorine, and with other salt-radicals, whether simple or 

 compound, and hence sulphurets, chlorides, and numerous 

 other series of metallic compounds. Of these series the sul- 

 phurets most resemble the oxides of the same metals ; the 

 chlorides and other series partake more strongly of the saline 

 character. Each metal, or class of metals affects combination 



* Renault, Ann. de Ch. et de Ph. t. 62, p. 368. 



