382 Gvoch and Blake — The Per chlorate Method 



perchlorate was dissolved to a clear solution in the alcohol 

 previously saturated with potassium perchlorate and to this 

 liquid mixture the weighed amount of solid potassium perchlo- 

 rate was added. The mixture in each case was thoroughly 

 shaken and filtered upon asbestos in the perforated crucible. 

 The precipitate, transferred by the use of the filtrate and 

 gathered in thin compact layer upon the asbestos felt, was 

 washed with a small amount of alcohol (about 5 cm^) applied 

 in portions successively with intermediate drainings. The 

 results, given in Table I, show that when a saturated solution 

 of potassium perchlorate in alcohol is used as the washing 

 liquid for precipitated potassium perchlorate in presence of 

 sodium perchlorate, there is the possibility that the precipitate 

 may be augmented by potassium perchlorate derived from the 

 washing liquid. 



Table I. 

 Treatment of the Saturated Solution of Potassium Perchlorate in Alcohol. 









Volume of 



KC104 



KCIO4 



Excess of 



saturated 



taken 



found 



KCIO4 found 



alcohol 



grm. 



grm. 



grm. 



cm^ 



0-1025 



0-1050 



0-0025 



50 



0-1020 



6-1036 



0-0016 



50 



0-1029 



0-1048 



00019 



50 



0-1012 



0-1033 



0-0021 



50 



As regards the solubility of potassium perchlorate in alcohol 

 carrying a small amount of perchloric acid, as recommended 

 by Wense,* it is evident that the solvent effect may be mod- 

 ified, without the use of a medium saturated with the salt to 

 be precipitated, by restricting the amount of liquid used in the 

 digestion, transfer, and washing the precipitate. We have, 

 therefore, tried the expedients (1) of keeping the volume of 

 liquid low and (2j of again using the first filtrate after the 

 digestion for transferring the precipitate to the filtering crucible, 

 completing the washing of the crystalline precipitate with a 

 very small amount of the washing liquid applied in successive 

 portions. The effects of these procedures, in the perchlorate 

 determination of potassium, rubidium, and caesium, are shown 

 in the following account of the experimental work. 



In all the tests, the carefully prepared alkali chlorides were 

 weighed in sm.all beakers, dissolved in water, and treated with 

 pure perchloric acid which distilled without residue. The 

 liquid was evaporated to the fuming point of perchloric acid. 

 For the smaller amounts (0*1 grin.) of material a single evap- 

 oration proved to be effective in converting the chlorides to 

 perchlorates. In tlie case of the larger amounts the residues 



* Loc. cit. 



