60 THE QUANTITATIVE SYNTHESIS OF ARGENTIC NITRATE, ETC. 



copper used for the reduction of the nitrous fumes. Less than 0.0002 

 gram of hydrogen retained by 300 grams of copper, or less than one part 

 in a million, would have been enough to cause this effect, hence it seemed 

 rash to assume that the water did not come from this source. As much 

 hydrogen as this might have come from a trace of moisture in the hun- 

 dred liters of carbon monoxide used for the reduction of the copper. 



The question thus raised was capable of being investigated. For this 

 purpose the mass of copper, reduced just as it would have been for one of 

 the preceding experiments, was twice oxidized by a very large volume of 

 pure ignited air dried with the usual potash towers and finally with phos- 

 phoric pentoxide. This air, having been already passed over red-hot 

 cupric oxide in a hard glass tube and thoroughly dried by pentoxide, could 

 hardly bring with it any water which could be taken up by the following 

 tube of the same material. On one of these occasions, 0.0009 gram of 

 water was found, and on another 0.0007 gram. Possibly some of this may 

 have come from the atmosphere during the manipulation of the tubes ; but 

 a similar amount must be supposed to have been taken during each of the 

 previous determinations. Hence it seems to be permissible to subtract 

 the average 0.0008 gram from the average result of experiments 25, 26, 

 and 27, namely, 0.0013 gram. This leaves only 0.0005 gram as the maxi- 

 mum amount of water held by 50 grams of carefully fused argentic nitrate, 

 introducing an error of only 1 part in 100,000. As the average of 

 the final series led to a value a trifle over 157.480 grams as the weight of 

 nitrate obtainable from 100.000 grams of silver, the correction to be applied 

 for water reduces the result only to 157.479. Possibly not even as much 

 water as this was present in the quantitatively made argentic nitrate, 

 because the relative surface exposed for drying was not so great in the 

 long, narrow tube just used as it was in the quartz flask employed for 

 experiments 10 to 15. 



This unimportant change in the synthetic result from 157.480 to 157.479 

 was the only apparent outcome of these tedious and often exasperating 

 experiments on the decomposition of the nitrate ; but in reality more was 

 shown by them. The experience furnished to the experimenters a strik- 

 ing example of the essential importance of taking as much care in deter- 

 mining a small correction as in determining the quantity to be corrected. 

 It moreover confirmed the impression that except in cases like the chloride 

 of zinc, when water acts chemically upon the substance, little or no water 

 is retained by most fused salts. If argentic nitrate, which at 200 is misci- 

 ble with water in all proportions, sets free so nearly all that it possesses 

 in a current of dry air at this temperature, it is much more likely that 

 other salts, fusing at a higher temperature and possessing a less attraction 

 for water, should be free from it after fusion. This is a reassuring con- 

 viction, well worth the trouble spent upon the point. 



