56 



THE QUANTITATIVE SYNTHESIS OF ARGENTIC NITRATE, ETC. 



matter is not, however, so simply settled ; the final testing of it cost much 

 labor. 



It has been ordinarily assumed that water is entirely expelled from crys- 

 tallized or evaporated salts upon fusion. This is in all probability the 

 case with sodic and potassic chlorides, and other salts which fuse at high 

 temperatures and show little affinity for water. Whether or not this was 

 the case with argentic nitrate, which at 210 is miscible with water in all 

 proportions, was a question which required experimental investigation. 



Besides the conservation of weight on fusion in a vacuum another argu- 

 ment may be adduced to show that most of the water has been driven out. 

 The combining weight of argentic nitrate seems to be nearly independ- 

 ent of the time of its fusion in a current of dry air, as is shown by the 

 following table. 



It should be stated that the last residue was slightly discolored, and 

 increased 0.00008 gram upon a subsequent evaporation with water and 

 nitric acid ; hence a real loss of weight during the extra period of fusion is 

 indicated; but this was probably due to decomposition of the salt rather 

 than to escape of water ; therefore the table bears out the contention stated 

 above. In any case this loss amounts to much less than a unit in the last 

 decimal place. 



Ordinarily, in the past, the investigator has been satisfied with such an 

 outcome and has gone no further. But in this case we were anxious to 

 leave no stone unturned; and accordingly a drastic method of treatment 

 was adopted, which permitted no trace of water to escape being weighed. 

 This was to decompose completely the argentic nitrate by heat, and to pass 

 the gaseous product of the decomposition through a weighed tube contain- 

 ing phosphoric oxide. 



A hard glass combustion tube was bent and drawn out in the manner 

 shown in figure 2, the space between C and D being packed with glass 

 wool. Into the space between B and C was then introduced about 50 

 grams of argentic nitrate which had been crystallized from nitric acid, 

 barely fused in porcelain, cooled, and pounded in a mortar. The tube 

 was heated to 220 in an air-bath for an hour in a stream of dry air passed 

 in through A. The argentic nitrate should now be in a condition some- 

 what comparable to that of the quantitative determination. Finally, a 



