318 Intelligence and Miscellaneous Articles. 



ONTHEABSORPTIONOFHEATBYABISMUTH AND ANTIMONY JOIN'T. 



To the Editors of tlie Philosophical Magazine and Journal. 

 Gentlemen, 

 In writing his remarks on the " supposed absorption of heat by a 

 bismuth and antimony joint," which occur in your last Number, 

 Mr. Adie appears to have forgotten the experiment of Lenz, in ■whicli 

 water was frozen at the point of junction, and the Centigrade ther- 

 mometer sunk to 3-5 degrees below zero. 

 Queenwood College, John Tyndali,. 



Sept. 21, 1852. 



ON THE PEROXIDE OF SILVER. BY F. MAHLA. 

 This substance, discovered by Hitter in 1804, is formed in a solu- 

 tion of nitrate of silver upon the positive wire of a galvanic couple, 

 while crystals of metallic silver are deposited upon the negative wire. 

 With the exception of the process described by Schonbein, by means 

 of the still very mysterious substance called ozone, it cannot be 

 obtained in any other way. Wallquist assigned to it the probable 

 formula of AgO* ; but some time afterwards Fischer pointed out, 

 that even when perfectly washed, this body gave off red nitrous 

 vapours when heated, and consequently that this formula could not 

 be correct. He moreover came to the conclusion that it contained 

 both nitric acid and water, 4AgO'- + AgO N0'' + 2H0. Malila has 

 recently examined this body in Wohler's laboratory. He obtained 

 it in the form of octohedral crystals, brilliant, but with curved 

 planes, which were frequently grouped together in the direction of a 

 principal axis in a prismatic form, and sometimes in narrow prisms 

 an inch long, which appeared at first to belong to a quite different 

 system. He never obtained it in tetrahedrons, which form it has 

 been stated by Grotthuss to assume. The crystals are of a grayish- 

 black colour, have a strong metallic lustre, and are very brittle. 

 Specific gravity 5*474. Heated to 240° F. they evolve pure oxygen 

 suddenly and with a kind of deflagration, at the same time falling to 

 powder. Further heated, red vapours of nitrous acid are given off, 

 and white metallic silver remains. Sulphuric and nitric .icids con- 

 vert it into ordinary silver salts of these acids with evolution of 

 oxygen. It is dissolved by ammonia with violent evolution of 

 nitrogen. It appeared possible that this body might consist of true 

 peroxide of silver, which, in consequence of its rapid formation, had 

 mechanically enclosed some nitrate of silver, to which the red vapours 

 observed on heating it were owing. However, Fischer and L. Gmelin 

 have shown that, even by the most careful washing, all the nitrate 

 cannot be removed. Mahla has also found this to be the case ; 

 likewise that during the washing there is a feeble disengagement 

 of oxygen ; and he considers that the crystals are a true compound 

 of AgO* with AgO N05. 



On analysis he found it to contain in 100 parts, — 



Foimd. Calculated. 



Silver 8M76 81-097 



Oxygen 16030 16-023 



Nitrogen 1765 1-753 



Water 1-166 1-127 



100137 100-000 



Assuming, as is most probable, that the nitrogen exists as nitric 



