THE DRYING AND WEIGHING OF THE POTASSIC CHLORIDE. 15 



containing fused salt was opened in the moist atmosphere of the beaker to 

 be used for the solution of the salt. 



At first the bottling apparatus so often used in the Chemical Laboratory 

 of Harvard College was employed to protect the fused chloride from mois- 

 ture during the determination of its weight, the chloride being contained in 

 a platinum boat protected by a glass-stoppered weighing bottle. Because, 

 however, the weighing room was not wholly constant in temperature or 

 in moisture, time and trouble were needed to obtain exact weighings, even 

 although the apparatus was always weighed by substitution against a 

 similar empty boat and bottle. The use of quartz weighing bottles proved 

 to be no advantage, indeed, if anything, a disadvantage. In either case, 

 if time enough were taken, satisfactory weighings could be made ; but 

 as time was especially precious, another device was used which wholly 

 overcame the trouble. 



This effective and satisfactory device consisted in the use of small 

 weighing bottles of platinum, shaped like the long Lawrence Smith 

 crucible, which were closed by small platinum capsules, fitting into the 

 bottles like ground stoppers. One of these bottles, containing the potassic 

 chloride, was supported by a loop of platinum wire in an inclined porce- 

 lain tube, and above it in the tube was placed its platinum stopper. Glass 

 stoppers fitted into each end of the porcelain tube, which was encircled 

 by a suitable furnace. After the potassic chloride had been dried for 

 a long time at a high temperature, just barely fused in nitrogen, and 

 cooled in a current of pure dry air, the stopper was shaken into place 

 and the platinum bottle quickly removed and placed in a desiccator. 

 This arrangement is essentially similar to the bottling arrangement of 

 Richards and Parker, except for the additional advantages that glass 

 is wholly eliminated and that the inclosed air-volume in the tube is much 

 smaller. Probably the burnished platinum joint is not as tight as the 

 ground-glass joint; but it is amply tight enough to prevent any appre- 

 ciable diffusion of moisture during the very brief exposure of the tube. 

 This was evident from the constancy of the weighings, which were made 

 by substitution against a similar empty platinum bottle kept in a similar 

 desiccator. The weighings were very quickly performed and were trust- 

 worthy. Before being used, the platinum bottles were repeatedly ignited 

 with pure sublimed ammonic chloride in order to remove iron ; they 

 remained satisfactorily constant in weight during subsequent experiments, 

 the one used for the fusion losing only 0.3 mg. in fourteen experiments, 

 or on the average 0.02 mg. in a single experiment. In one experiment, 

 where oxygen was present during the fusion, as much as 0.3 mg. was 

 taken from the boat, the platinum being plainly visible on solution. This 

 was of course not used for analysis. 



