CRITICAL EXPERIMENTS FOR DETERMINATION OF POTASSIUM, ETC. 573 



of the clear liquor, and, by its analysis for platinum and fixed chlorine, prove the 

 absence of excess, or determine such small excess as there might be, of either 

 reagent. But very little chloroplatinate did settle out. We therefore added 

 enough of absolute alcohol to nearly fill the bottle, shook up the contents, and 

 allowed to stand, stopper on, over night. Next morning the whole was 

 weighed, as much as possible of the clear liquor drawn off, weighed, (in a 

 stoppered phial), and analysed for platinum, total chlorine, and fixed chlorine. 

 For this purpose, the solution (after addition of water but without removing its 

 alcohol), was kept at a temperature near to, but below, its boiling-point, within a 

 conical flask, through which a very slow current of hydrogen was constantly 

 passing. The out-going hydrogen was made to bubble through a quantity of 

 water contained in a bulbed U-tube, to catch any hydrochloric acid that might 

 go off. Let us at once state that no chlorine was found in this wash-water after 

 the experiment. The platinum was filtered off and weighed ; the filtrate diluted 

 to a known weight, and aliquot parts used for the determination of the fixed and 

 total chlorine. As there was not enough of material for repeating either deter- 

 mination, the chlorine, in each case, was precipitated with a known weight of 

 standard nitrate of silver, the precipitated chloride of silver weighed, and the 

 excess of silver in the filtrate determined by Volhard's method, to check 

 the gravimetric determination. From the weight of platinum obtained, the 

 corresponding weight of chloroplatinate of potassium was calculated, the re- 

 sulting number multiplied by the ratio of bottle contents to liquor analysed, 

 and the result deducted from the total chloroplatinate (solid or dissolved) 

 calculated from the total platinum used, to obtain a first approximation 

 to the weight of solid chloroplatinate in the precipitation bottle, at the 

 time when the liquor was withdrawn. The result, when subtracted from the 

 weight of the total contents, gave an approximation to the weight of the total 

 mother-liquor. From this weight a second approximation to the dissolved 

 chloroplatinate was obtained, and thus a second approximation to the weight 

 of the solid chloroplatinate, and consequently also to that of the mother-liquor. 

 This second result served for the reduction of the chlorines formed in the 

 drawn off part to the total liquor. 



We might have stated before that the platinum solution, before being 

 used, was analysed to find the quantities of platinum, total chlorine, and fixed 

 chlorine present in the weight of reagent employed. To enable the reader to 

 form his own opinion on the probable uncertainty in the final results, we quote 

 the following numbers : — 



Found, for the total liquor drawn off — 



Total Chlorine. Fixed Chlorine. 



Gravimetrically, .... 0-38263 0-02676 



Titrimetrically, .... 0-38240 0-02675 



Means (adopted), . . . 0-38251 0-02675 



