494 



precautions into water. After straining off the precipitated silica, the 

 acid was boiled down with chlorate of potassium (and not perchlorate, 

 as Serullas advises), added in such quantity that for every kilogramme 

 of fluor-spar 600 grammes of chlorate was present. On heating the 

 mixture, the liberated chloric acid undergoes quiet decomposition, 

 chloric oxide, and probably other oxygen compounds of chlorine, 

 escaping as gas, whilst aqueous perchloric acid remains in the liquid. 

 After the mixture has cooled, the aqueous acid was decanted from the 

 insoluble fluosilicate of potassium, and the clear liquid concentrated by 

 boiling until the perchloric acid began to volatilize. The acid was 

 then distilled, and freed from chlorine by perchlorate of silver, and 

 from sulphuric acid by perchlorate of barium. According to this 

 method, 4 kilogs. of chlorate of potassium yielded 500 grammes of 

 pure concentrated aqueous perchloric acid. 



The aqueous acid thus prepared is a colourless, heavy, oily liquid, 

 in appearance undistinguishable from oil of vitriol ; its composition 

 and properties will be hereafter described. 



From this substance I have succeeded in preparing two definite 

 compounds. One of these is the liquid pure perchloric acid, Cl O 4 H, 

 an interesting body which was previously unknown ; and the other 

 is the monohydrated or crystallized acid, Cl G 4 H + H 2 O, originally 

 discovered by Serullas, but obtained by him in such small quantities 

 that he was unable to determine its composition. 



If aqueous perchloric acid be distilled with four times its volume of 

 oil of vitriol containing 98*5 per cent, of real acid, decomposition 

 begins at a temperature of about 110 C. ; dense white fumes are 

 evolved and escape, whilst a yellowish, mobile, easily condensible liquid 

 is found in the receiver. If the distillation be continued, the tem- 

 perature gradually rises to 200 C., and a thick oily liquid distils over, 

 which, on coming into contact with the more volatile liquid in the 

 receiver, immediately unites with it, forming a white, solid, crystalline 

 mass. Both the first and the last portions of the distillate thus pre- 

 pared were found to contain sulphuric acid mechanically carried over, 

 and were therefore unfit for analysis. In order to obtain the sub- 

 stances in a pure state, the crystallized acid thus prepared requires 

 redistillation. Heated, however, to a temperature of 110 C., the 

 crystals themselves undergo a decomposition similar to that just de- 

 scribed, a strongly fuming volatile liquid first distilling over, and the 



