440 Miscellaneous Intelligence, 



22. Volatilization of Silver. — The following case of the volatili- 

 zation of silver is noticed by Mr. Princep, in a paper on the mea- 

 surement of high temperatures. He had long* used a pyrometric 

 bar, carrying at one extremity an index, made on the compensation 

 principle, of silver and gold. " The heat communicated to this com- 

 pound index can never have much exceeded the melting point of 

 lead, or about 700° F. ; and yet the surface of the gold has gra- 

 dually become perfectly discoloured, and apparently penetrated by 

 the silver in the same manner as would have been produced by 

 mercury at a common temperature. This effect commenced on the 

 edges of the slip of metal, and has now advanced nearly over the 

 whole surface of the slip of gold, giving it the appearance, under 

 the microscope, of being studded over with hard tubercles of a leaden 

 colour. The golden yellow, where it is not yet thoroughly changed, 

 has become green, like that of an alloy of gold and silver. The 

 impregnation has extended to a considerable depth in the gold, and 

 consequently the index has become less and less sensible to changes 

 of temperature. But I should remark, that at the fixed end of the 

 plate, where a piece of platina foil had been joined, to strengthen 

 and support the index, no discolouration has taken place, the pla- 

 tina covering seeming to shelter the gold from the argentine 

 vapours. I should also remark, that the two metals were origi- 

 nally quite pure, and were united without any alloy by simply laying 

 an ingot of silver over one of gold, and heating the two until the 

 former just began to melt; the compound ingot was then lami- 

 nated.*' The bar had been used constantly for nearly five years. 

 Mr. Princep omitted to keep any note of the original weight of the 

 bar, by which any positive loss might have been ascertained. 



Query. Might not the silver in this case have entered and per- 

 meated the gold by a process analogous to that which takes place 

 with carbon in cementation and the formation of steel ? — Ed. 



23. Crystallization of Argentiferous Salts. — As all the salts of 

 silver are soluble in ammonia, and only the chloride, the nitrate, 

 and the sulphate, form triple compounds with ammonia, M. Fischer 

 proposes this method for the production of crystals of what are 

 called the insoluble salts, considered only in relation to water. A 

 great number of these may be thus obtained in definite forms. — 

 Kastner's Archives. 



24. Argentiferous Precipitate analogous to the Purple of Cas' 

 sius. — If dilute solutions of nitrate of silver, and nitrate of tin, be 

 mixed, the fluid gradually becomes yellow, then brown, reddish 

 brown, and ultimately dark purple. On the addition of dilute sul- 

 phuric acid, a brownish purple precipitate is deposited, consisting 

 of the oxides of tin and silver, and analogous in its nature to the 

 purple of Cassius. If no acid be added, the fluid becomes colourless 

 by degrees, and ultimately furnishes very little precipitate,— .4 ?i7^. 

 der Phys, 1828, p, 285. 



