﻿12. STUDIES ON PERCHLORIC ACID (IV)— Distillation of 

 Potassium Perchlorate with Sulphuric Acid. 



By Fraxk C. Mathers, Ph.D., Assistant Professor of Chemistry. 



Introduction. The difficulties in obtaining a satisfactory supply 

 of perchloric acid for experiments in the Indiana University chemical 

 laboratory led to the research which is described in this paper. 

 At the present time, the use of perchloric acid in laboratory methods 

 is seriously restricted by high cost, and its use in any commiercial 

 process is impossible. The success of the methods for the electro- 

 lytic deposition of metals from perchlorate baths ^ really depends 

 upon the economical preparation of perchloric acid. 



Perchloric acid may be made very easily by the treatment of 

 sodium perchlorate with concentrated hydrochloric acid. The con- 

 ditions for obtaining maximum yields were published in a previous 

 paper. 2 The only objection to this method is that the sodium 

 perchlorate is an expensive starting material. Potassium perchlorate, 

 which is a cheaper starting material, will not give perchloric acid 

 when treated with hydrochloric acid. The simplest method of 

 making perchloric acid from potassium perchlorate is to distill 

 with an excess of sulphuric acid. 



Method of Analysis of the Distillate. Sulphuric acid was de- 

 termined by precipitation as barium, sulphate. The total acidity, 

 after correcting for the sulphuric acid present, was calculated as 

 perchloric acid. Chlorides and free chlorine, which were deter- 

 mined in a few cases, were present in such small amounts that 

 these determinations were discontinued. Non-volatile matter, 

 which was determined in a few experiments, was about 0.065 

 gram for each 100 grams of potassium perchlorate used. 



Experiments. The distillation of potassium perchlorate with 

 sulphuric acid under atmospheric pressure gave yields of perchloric 

 acid which varied from 54 to 74 per cent. No conditions were 

 found which would give satisfactory yields. The distillates were 

 colprecl pale yellow and much chlorine or oxides of chlorine were 

 evolved during the distillation. The presence of water was neces- 

 sary for even fair yield. Large amounts of water were of no ad- 

 vantage because the excess was distilled out before any perchloric 



1 Mathers, Chemiker-Zeitung, No. 148, 1316 (1910). 

 Mathers, Indiana University Studies, I, No. 4, 30 (1910). 



Mathers, Transactions American Electrochemical Society, XVIII, 261 (1910). 

 Mathers and Germann, Indiana University Studies, I, No. 5, 41 (1910). 

 blathers and Germann, Transactions American Electrochemical Society, XIX, 69 (1911) 

 Mathers and Overman, Ibid, XXI (1912). 

 = Mathers, Indiana University Studies, I, No. 3, 24 (1910). 

 Mathers, Journal American Chemical Society, XXXII, 66 (1910). 



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