46 § 44. basp:s axd acids with REAGEinrs. . 



h. Determination as potassic Sulphatc. — The solution 

 being freed from other metals and from non-volatile acids, 

 as directed in each special case, evaporate it to dryness 

 and ignite the residue in a platinum crucible, as directed 

 for the ignition of potassic chloride, except tliat it may 

 be more strongly heated at the close of the operation. 



If volatile acids, such as hydrochloric, nitric, or acetic, 

 are present in tlie solution containing the potassium to be 

 determined, sufficient sulphuric acid must be added before 

 evaporation to expel them; in order, however, to avoid 

 the disagreeable operation of expelling a large excess of 

 sulpliuric acid also, it is well to add but little at first ; the 

 evidence that enough has been used will be found in the 

 evolution of abundant white acid fumes towards the close 

 of the evaporation ; if these fumes do not appear, of 

 course a little more acid must be added, and the evapora- 

 tion continued. 



After igniting the residue in the j)latinum crucible 

 gently for a little while, put in a small fragment of well 

 dried amnionic carbonate, and ignite again while the 

 crucible is loosely covered, very gently at first, and then 

 gradually raise the heat to a full red ; repeat this addition 

 of ammonic carbonate and the subsequent ignition as 

 lonoj as there is any chanire in weig^ht. 



The ignition Avith ammonic carbonate facilitates the ex- 

 pulsion of the second equivalent of sulphuric acid from 

 the potassi-c bisulphate, and it should be used in the man- 

 ner indicated whenever free sulphuric acid was present in 

 the solution that was evaporated. The residue of potassic 

 sulphate contains 44.89" |„ of potassium, or 54.08° |^ of 

 potassa. 



c. The determination of potassium as potaSSic platinic 

 chloride depends upon the insolubility of this compound 

 in alcohol. 



The solution being freed from all except potq,ssic and 

 sodic chlorides, and, according to Stohraann, calcic and 



