THE PURITY OF THE FUSED ARGENTIC NITRATE. 



59. 



tallized from nitric acid, filtered, precipitated with formate, washed free 

 from ammonium salts, and fused on lime in the blast. The buttons were 

 etched and dissolved in freshly distilled nitric acid in Jena glass, and 

 the salt was crystallized with ample protection against ammonia, dried 

 centrifugally and kept in a clean, tight desiccator. There was no ammonia 

 in this product. Before using it was fused in platinum. 



In the first determination of this series the argentic nitrate was heated 

 too hot (520) and the gases came over so fast that the reduced copper 

 was only superficially attacked ; even so it was vastly more efficient than the 

 gauze. Because, however, some nitric peroxide still escaped, this experi- 

 ment also had to be rejected, a part of the 0.004 per cent impurity which 

 it indicated being undoubtedly due to nitrous fumes. 



The apparatus was now improved by sealing off the end (A) of the tube 

 after the argentic nitrate had been fused for a long time in a current of dry 

 air. Moreover, the last trace of rubber exposed to nitrous fumes was 

 eliminated by providing an accurately ground joint between the decom- 

 position tube and the copper oxide. The process was conducted so slowly 

 at 490 that the argentic nitrate could be entirely decomposed to pure 

 spongy silver without exhausting all the copper. Care was taken to have 

 the very pure argentic nitrate in a state comparable to that used in the 

 determinations. The salt after its preliminary treatment in platinum still 

 contained a few crystals of unfused nitrate ; accordingly in the tube it was 

 heated evenly at 220 with shaking to dislodge steam bubbles, exactly as 

 the determinations had been. Under these conditions reliable results 

 were obtained. In No. 25, a second weighed pentoxide tube placed in 

 tandem with the first showed no gain in weight; hence the first tube 

 caught all the water vapor. The remaining nitrogen was driven out by 

 pure dry air before weighing. That water vapor was actually present 

 was shown by the "melting" of phosphoric pentoxide in the first tube. 



Water Obtained by Decomposition of Argentic Nitrate. 



Thus it is clear that less than 0.003 per cent of water was held by the 

 argentic nitrate after fusion. There was only one other source from 

 which this milligram or so of water might have come, namely, from the 



