58 THE QUANTITATIVE SYNTHESIS OF ARGENTIC NITRATE, ETC. 



before passing over the copper ; it had been heated in the dry air to remove 

 moisture. 



To eliminate the possibility of water in the copper gauze and to test the 

 apparatus, a blank run was made, removing the decomposition tube, and 

 oxidizing the copper with dry air. Here the pentoxide tube lost 0.0004 

 gram, a result which indicated no error in that part of the process. 



It is not worth while to record the individual experiments by which the 

 gradual improvements in apparatus and manipulation were tested, tire- 

 some and time-consuming as these were in execution. By the time seven 

 experiments had been performed, it was clear that the fused argentic nitrate 

 could not contain over 0.004 per cent of water. Even of this small amount 

 a part was undoubtedly due to nitric peroxide ; for the copper gauze was 

 not enough to effect a complete decomposition of the gases. Passing car- 

 bon monoxide through the apparatus while the decomposition was in prog- 

 ress lengthened the effective life of the reduced copper, but introduced 

 other complications; and the addition of a second tube of hot gauze, a 

 meter long, was still inadequate. 



The next step was to secure a copper surface so large that all the nitro- 

 gen oxide resulting from the complete decomposition of 50 grams of 

 argentic nitrate could be removed, and this without increasing the compli- 

 cations of the apparatus. Powdered copper oxide looked promising as a 

 source of this metal, but it must be made from pure materials to avoid 

 the presence of detrimental impurities. Pure electrolytic copper (Merck) 

 was dissolved in nitric acid, evaporated to dryness in porcelain, and very 

 gradually ignited, with constant stirring, to powdery oxide. A hard glass 

 tube 30 cm. long and 3 cm. internal diameter was used to contain it ; the 

 ends were drawn down conveniently and the oxide was reduced at a very 

 moderate heat with carbon monoxide, prepared as usual, except that it 

 was finally dried with pentoxide. Nearly 300 grams of copper oxide were 

 present ; therefore, the process was very tedious, since the gas had to pass 

 through its purifying train at a moderate rate of speed. With this large 

 mass of finely divided copper the glass wool (from C to D in the dia- 

 gram) was no longer necessary, therefore it was no longer used. No trace 

 of powdered nitrate ever appeared beyond the copper. 



A clean pentoxide tube, with glass stopcocks, was refilled with resub- 

 limed pentoxide and glass wool ; dry air was passed through for ten min- 

 utes to assure constancy. A duplicate tube was also prepared for a coun- 

 terpoise, and extraordinary precautions were taken in protecting and 

 weighing these tubes. As another precaution it seemed also expedient to 

 prepare argentic nitrate nearly as pure as that used in the determinations 

 for fear of hygroscopic nitrates, silicic acid, and ammonium salts, which 

 would yield water when decomposed. A moderately pure salt was recrys- 



