386 Gooch and Blake — The Per chlorate Method. 



Table V (continued). 



KCl 



taken 

 grm. 



EbCl 

 taken 

 grm. 



CsCl 

 taken 

 grm. 



Per- 

 chlo- 

 rate 

 found 

 grm. 



Theory 



for 



perchlo- 



rates 



grm. 



Error 

 grm. 



HCIO4 



(70^) 

 cm^ 



Filtrate 

 cm^ 



Three evaporations with intermediate solution, in platinum: 

 transfer by means of the filtrate. 



0-1038 0-1000. 0-1025 0-4873* 0-4873 0*0000* 3X0*4 20 + 5 

 0-1010 0-1000 0-1018 0-4817* 0-4811 +0-0006* 3x0-4 20 + 5 



The results of the experiments recorded go to show (1) that 

 the use of an alcoholic liquid saturated with the substance to 

 be precipitated is unnecessary to the attainment of good analyti- 

 cal results; (2) that it is practicable to so restrict the volume 

 of the washing liquid (97 per cent alcohol containing O'l per 

 cent of perchloric acid) that the solubility of the precipitated 

 perchlorates is insignificant for practical purposes; (3) that a 

 single evaporation with a moderate excess of perchloric acid 

 (O'l cm^ for every 0*1 grm. of salt) is not sufficient to convert 

 considerable masses of alkali chlorides (e. g., 0-3 grm.) com- 

 pletely to perchlorate, and that in such a case the residue of 

 the first evaporation with perchloric acid should be dissolved 

 in the least amount of water, another portion of perchloric acid 

 added, and the evaporation repeated; (4) that in separations 

 of the larger amounts of insoluble perchlorates (0'3 grm.) from 

 sodium perchlorate the residue left after digestion of the nearly 

 dry mass of perchlorates in the washing liquid and decanta- 

 tion should be dissolved in a small amount of water and the 

 process of evaporation and extraction repeated; (5) that, in the 

 case of rubidium at any rate, digestion of the residue for fifteen 

 or twenty minutes with the washing liquid before effecting the 

 transfer is advantageous. 



It is to be noted that the evaporation of large amounts of 

 perchloric acid in glass may result in a considerable action upon 

 the glass and it has been found that perchloric acid which has 

 stood a long time in glass may yield an appreciable residue on 

 evaporation. 



* Upon dissolving these residues, again precipitating, and weighing, errors 

 found were —0-0004 grm. and +0'0004 grm. respectively. 



