36 ATOMIC WEIGHTS OF SODIUM AND CHLORINE. 



various samples of salt were analyzed by methods of known precision. 

 The temptation to vary two conditions in a single new experiment 

 is thus easily avoided. The detailed description of every step of the 

 analytical process follows. 



It was soon found that salt when free from excess of acid can be 

 fused in a platinum crucible in the air without either attacking the 

 crucible to an important extent, or becoming appreciably alkaline. 

 Quantitatively, it was later proved, as will be shown, that salt thus 

 prepared is identical to that fused in a platinum boat in a vacuum and 

 transferred and weighed in the familiar ' ' bottling apparatus ' ' which 

 has served so conveniently for hygroscopic substances. It was found, 

 moreover, that a crucible full of salt thus prepared did not gain in 

 weight during the operation of weighing, on account of the dry winter 

 atmosphere of the steam-heated weighing room. Probably this would 

 not have been the case in a moist climate; but being the case, it facil- 

 itated greatly the present work. 



The crucible generally used for fusing the salt was, of course, pre- 

 viously freed from iron, and during twenty-three fusions it lost only 

 0.47 milligram, or 0.02 milligram each time. It is possible that a por- 

 tion of the weight was lost by volatilization during the preliminary igni- 

 tions of the crucible, when it was being prepared for weighing alone ; 

 but probably most of this trace of platinum went into solution in the 

 salt. The weight of the crucible before fusion was always taken as 

 the true one, however ; therefore even this slight possibility of loss of 

 course could not affect appreciably the quantitative result. 



During the fusion of the salt the crucible was inclosed in a larger 

 covered Berlin porcelain crucible, especially made to fit it, and heated 

 by a blast lamp in a small clay furnace. The products of combustion 

 were suitably deflected, so that only pure air should be in contact with 

 the salt in the crucible. The fused salt was cooled in a desiccator in 

 the balance room, and the weighing was conducted by the substitution 

 of a suitable tare-crucible, as usual. 



In order to avoid all risk of accidental loss, the salt was dissolved 

 from the crucible by placing it in a large covered beaker, and after 

 covering it carefully with water, agitating it gently from time to time 

 until solution was complete. This solution thus carefully prepared 

 was transferred Ito a 2 -liter Erlenmeyer flask with a well -ground 

 glass stopper, where it was diluted to suitable volume (over 5 liters per 

 mol). Here it was precipitated by the at least equally dilute argentic 

 nitrate in excess. The precipitate was freed from the supernatant 

 mother liquor by filtration as soon as it had cleared enough to make 

 this separation possible. Promptness is needed in order to avoid the 



