50 THE QUANTITATIVE SYNTHESIS OF ARGENTIC NITRATE, ETC. 



THE SYNTHESIS OF ARGENTIC NITRATE. 



The materials having been prepared, the next step was to combine them. 

 This combination must take place in a vessel wholly free from a sus- 

 picion of solubility on the one hand, and arranged so as to prevent loss of 

 material on the other hand. At the same time, it was important to be able 

 to evaporate and to weigh the argentic nitrate in the same vessel. After 

 a careful consideration of the somewhat conflicting claims of these require- 

 ments it was decided to carry out the process in small round-bottomed 

 flasks of fused quartz of from 0.03 to 0.04 liter capacity ; with necks 

 11 cm. in length and 6 to 9 mm. in internal diameter. Collars of platinum 

 wire provided with loops permitted the suspension of these flasks from 

 the hook of the Troemner balance. Before weighing, they were heated in 

 the oven to be presently described to 250 for at least half an hour, a 

 moderate air-current sweeping through them all the time. The cover- 

 ings were then lifted, and each flask was removed by a hook of platinum 

 wire sealed into a glass rod, and transferred to a large desiccator pro- 

 vided with a suitable support. Two flasks similar in weight and surface 

 were treated in the same way and kept in the same desiccator. After 

 two hours near the balance the first flask was weighed against a tare, its 

 weight being determined by substitution of the first by the second flask 

 and a few small weights. Upon removal from the desiccator both flasks 

 absorbed moisture from the air, often to the extent of 0.0001 gram, but 

 they soon reached constancy with respect to one another, which was all 

 that was needed. No final weighings were made when the hygrometer 

 in the weighing-room stood above 40, and under these circumstances 

 flasks could be weighed on successive days with variations not exceeding 

 0.00003 gram. 



A new Troemner balance, sensitive to 0.01 mg. was available for the 

 research. The brass weights were carefully standardized at the begin- 

 ning of the year, and again upon starting the final series ; and the rider 

 also was calibrated, and the necessary correction employed. For cor- 

 rection to the vacuum standard 0.000132 was added to each apparent 

 gram of argentic nitrate, and 0.000030 was subtracted from each apparent 

 gram of silver. This was on the assumption that the two specific gravities 

 concerned were respectively 4.35 and 10.49, that of the brass weights 

 being 8.3. 



The silver was now weighed by substitution, and carefully pushed 

 down the neck of the flask, which was held meanwhile in a horizontal 

 position to avoid breakage. Next the whole was transferred to a large, 

 clean, empty desiccator, whose sides had been moistened ; and the flask was 

 laid on a suitable support of glass and platinum tilted 45 from the ver- 



