of the Elements. 493 



and consequently with silver, — 



Kopp, however, calculates with silver, — 



All three oxides yield a regulus with great facility. We should 

 anticipate that the oxides and salts of silver would decompose 

 most readily, then those of lead, then those of mercury. Taking- 

 all the reactions into consideration, however, it appears that 

 mercurial oxide and salts are more easily decomposed than 

 plumbic, though several reactions point to an opposite conclusion. 

 Thus, hydrogen gas decomposes oxide of lead at a temperature 

 but a little above 100° C. (Winkelblech). Potassium and sodium 

 at temperatures below their melting-points decompose oxide of 

 lead (Gmelin). Potassium and sodium heated to their melting- 

 points decompose mercuric oxide (Gay-Lussac and Thenard, &c.). 

 Oxide of silver is decomposed at a red heat, but is formed at a 

 more intense heat. Oxide of mei'cury volatilizes at a red heat 

 and is decomposed ; it is produced at a lower temperature. 

 Oxide of lead is certainly volatile at an intense heat, and is pro- 

 bably decomposed ; it is produced at a red heat. All three metals 

 form hydrates which are perceptibly soluble in water, and mani- 

 fest alkalinity to test-paper. Mercury forms a dinoxide and 

 corresponding disalts. Lead forms a most indubitable dinoxide 

 and disulphide. Silver also appears to form a dinoxide (Faraday) 

 and corresponding disalts (Wohler). The formation of dichlo- 

 ride of silver at any rate cannot be questioned. Mercury does 

 not form any higher oxide than the protoxide. Lead forms a 

 binoxide and intermediate oxides. Silver moreover forms a per- 

 oxide which is apparently a binoxide, and has been examined by 

 many chemists. The protosulphides of the three metals have a 

 general analogy of properties. That of mercury is red at ordi- 

 nary temperatures, black at 300° C, and by a stronger heat 

 sublimes. The sulphide of lead is black and volatilizable ; that 

 of silver black and fixed. All three are with difficulty attacked 

 by acids. The three protochlorides exhibit a marked similarity 

 and gradation of properties. In all three the atomic volume of 

 the chlorine is the same, despite the opinion of Kopp to the con- 

 trary : thus with silver we have — 



Calculated. Experimental. 



/o^ w .. = 5-50 5-55Boullay, 550 and 55-7 



. l'^0+196 [Karstcn; 



with lead, — 



}J?^IL = 5-54 5-68 and 5-8 Karsten ; 



114+196 



