THE PURITY OF THE FUSED ARGENTIC NITRATE. 57 



weighed pentoxide tube was attached at D, and the temperature raised to 

 500. Yellow oxides of nitrogen came over, also a fine gray dust caused 

 presumably by the bursting of 

 bubbles of decomposing salt. 

 After an hour the pentoxide 



tube was removed, swept out Fig 2 _ Tube ^ Decomposi L O f Arctic Nitra e . 

 with air, and weighed again. aboul one - el hth actual 81ze - 



A trace of the gray dust had been carried in, and suggested a slight 

 gain in weight, but by no means enough to account for the great 

 increase of weight, 0.012 gram. This was finally traced to the adsorption 

 of nitrous fumes by the pentoxide, 2 mg. being lost upon passing dry 

 air over the tube for an hour, and the rest giving a very strong test for 

 nitrous acid after being dissolved in water. 



In the effort to eliminate this seriously disturbing effect, recourse 

 was next had to spirals of copper gauze heated in a combustion tube, in 

 order to abstract the oxygen from the nitric oxide, leaving only nitrogen. 

 It is well known that metallic copper adsorbs hydrogen ; hence the spirals 

 were first superficially oxidized in a stream of dry air, and then reduced 

 by pure dry carbon monoxide. This was generated by heating the purest 

 oxalic and sulphuric acids of commerce together, the carbon dioxide being 

 absorbed by a generous train of pure concentrated potash solution, and the 

 monoxide dried first by a tower of concentrated sulphuric acid, with 

 beads, and finally by two towers of pounded potash. The resulting cop- 

 per should be above the suspicion of containing any considerable amount 

 of hydrogen or moisture. The argentic nitrate was treated as before, 

 and the decomposition was continued until traces of yellow fumes were 

 noted coming past the copper. This meant that nitric oxide had been 

 coming over for some time, since the last part of oxygen is harder to 

 detach than the first. When swept out with air, the gas in the pentoxide 

 tube turned yellow, but it was not then supposed that much nitric oxide 

 could be absorbed by the pentoxide in so short a time. Nevertheless, 

 nitrous acid was found upon solution, even although the gain in weight 

 was only a third as great as before. 



Efforts were now made to reduce accidental water from rubber, etc. 

 All joints were made to overlap, so that the rubber surfaces exposed to 

 nitric oxide might be small, and large asbestos screens kept them from 

 being overheated by the adjacent furnaces. Fresh sublimed pentoxide 

 was used in the weighing-tube, which was carefully imitated as to volume 

 and surface by a similar tube, to be used as a counterpoise in weighing; 

 both were opened after coming to the temperature of the balance-room, 

 wiped with a clean, slightly damp cloth, and weighed by substitution. A 

 substantial plug of glass wool in the decomposition tube strained the gases 



