On iie Soluim and Oxygenation cf Tift, 515 



XIV. 



ExtraB of a Memoir of Proujiy entitled Enquiries concerning Tin. By CITIZEN DaRCET,* 



H E author of this memoir obferves, in the firft place, that he confiders his work as a 

 fupplement to that of Pelletier, on the different degrees of oxygenation which tin can acquire, 

 when diflblved in acids. 



When tin is diflblved without heat, in very weak nitric acid, it acquires a degree of oxygena- 

 tion, different from that which it would obtain if diflblved in a concentrated acid, or if heat 

 had been employed. In the firft cafe, the nitric acid is not decompofed, and afibrds but little 

 oxygen; but this is not the cafe with the water, which in fad, afibrds the quantity necelTary 

 for its oxygenation. 



This folution, which is of a yellow colour, gradually precipitates, more efpecially if it be heat- 

 ed, and the feparation of the tin is made without re-a£tion, for there is no difengagement of 

 nitrous gas ; and if it be faturated with cauflic pot-afb, there is a difengagement of ammoniac, 

 as was already obferved by Bayen and by Pelletier. The oxyde of tin, as well that portion 

 which remains fufpended in the fluid, as that which is precipitated, and re-diflblved in muriatic 

 acid, equally decompofe the fuperoxygenated muriate of mercury, and the mercurial oxydes, 

 &c. being very different, in this refpedt, from the oxyde of tin, which is precipitated from the 

 folution, in concentrated nitric acid, or the folution which has been made with heat. In this, 

 the nitric acid is decompofed, and the precipitate is infoluble in the muriatic acid, and no 

 longer a£ls upon corrofive fublimate, or the oxydes of mercury. This difference arifes from the 

 circumflances, that in the firfl cafe, the oxyde of tin, whether it remain in the liquor, or fall 

 down, is oxyded to the minimum, as Prouft affirms, and in the fecond cafe, to the maximum. 

 Hence it is, that in the firfl cafe, there is no difengagement of elallic fluid, whereas in the 

 fecond, the difengagement is conC4erable. 



When an acid of the ftrength of 25 or 30 degrees is ufed (fp. gr. 1,23), the folution is fa 

 violent, that there does not remain an atom of tin in the fluid, but the precipitate is oxyded to 

 40 parts of oxygen ; but when the very weak nitric acid is ufed, or the folution is made with- 

 out heat, the metal is oxyded only to 30. 



It is afcertained by hepatic water, that all the tin is feparated from the acid; for this re-agent, 

 will totally precipitate tin, copper, or lead, if the fluid contain any. Prouft has obferved, that 

 this re-agent may prove eminently ufeful. For example, fuppofe a folution to contain lead, 

 copper, zinc and iron, the hepatic liquor will feparate them all in fucceflion; firfl the copper, 

 then the lead, next the zinc, and laft of all the iron, with jhis remarkable event, that the iron 

 which was oxyded to the maximum in the folution, is thrown down at the minimum, and is 

 precipitated green, by ammoniac and by lime. This happens, becaufe the hepatic water feizes 

 a portion of the oxygen from the oxyde, and becomes decompofed, leaving the iron at the lefs 

 degree of oxygenation. 



It is known, that very fetid hydrogen is extricated, during the folution of tm in the muri- 



* Annales de Chimie, XXVIII. 113. 



atlc 



