14 THE ANALYSIS OF POTASSIC CHLORIDE. 



NITRIC AND HYDROCHLORIC ACIDS. 



Very carefully tested preparations of commerce were used as the raw 

 materials in the preparation of these acids. They were redistilled with 

 platinum condensers until they were fully pure enough for the purposes 

 for which they were needed. The hydrochloric acid had been shown 

 in the research on sodium to be free from bromine or iodine. 



WATER. 



This substance, because it is used in larger quantities than any other, 

 must be especially pure. All the water used, either for preparation or 

 analysis, was twice distilled, once with alkaline permanganate and once 

 alone. For the best work a platinum condenser was used. All that was 

 needed for analysis was tested in the nephelometer immediately before use. 



THE DRYING AND WEIGHING OF THE POTASSIC CHLORIDE. 



The final preparation of the salt for analysis is given a special chapter 

 to itself, because the proper execution of this feature is of very great 

 importance, not less than the purification of the material. It is clearly 

 useless to separate 0.001 per cent of a metallic impurity if 0.01 per cent 

 of water is allowed to remain in the salt. 



Obviously, superficial drying can not remove the imprisoned moisture 

 in the crystals, hence they must be fused. 1 Except in a few preliminary 

 experiments, where a common platinum crucible was used, this fusion 

 was conducted in a platinum boat or open bottle contained in a porcelain 

 tube through which a current of nitrogen was passing. The experience 

 in a number of similar cases, that the simultaneous presence of oxygen 

 and traces of hydrochloric acid inclosed in the crystals is likely to cause 

 perceptible corrosion of the platinum boat, was confirmed in this case ; 

 hence an inert gas \vas needed. The nitrogen was prepared by the w r ell- 

 known method of Wanklyn, by passing air charged with ammonia 

 over red-hot copper. The excess of ammonia was carefully eliminated 

 by washing the gas with much dilute acid. Because fused sodic chloride 

 was found to be essentially free from dissolved nitrogen, we did not think 

 it necessary to fuse this very similar potassium salt in a vacuum. 



Potassic chloride, although not so hygroscopic as some other salts, 

 used in similar researches, is nevertheless far too hygroscopic to weigh 

 safely when directly exposed to the air of the balance room. Its ten- 

 dency to attract water was seen in perceptible crackling when the tube 



a Richards, Zeit. phys. Chem., 46, 189 (1903). 



