16 Prof. Sir C. A. Cameron and Mr. J. Macallan. [May 2, 



then inverted and pushed down into the flask, so that when the open 

 end wa,s below the surface of the acid, the closed end extended suffi- 

 ciently far into the neck of the flask to prevent the tube from being 

 thrown down by the ebullition of the liquid. The vapour given off 

 from the acid within the tube became gradually expanded as the 

 temperature rose, and passed in a stream of bubbles through the acid, 

 keeping it well agitated. The tube also served the purpose of pre- 

 venting splashing from the boiling acid up into the neck of the small 

 flask. 



Some selenic acid, which had been previously partially concentrated, 

 was kept in an open dish on the water-bath f orf our hours and its strength 

 then determined : 0*6364! gram required for neutralisation 14" 72 c.c. 

 of seminormal soda solution, equivalent to 83*68 per cent, of selenic 

 acid — a strength intermediate between a monohydrate and a dihydrate. 

 The acid thus obtained at 100°, under the ordinary pressure of the 

 atmosphere, was stronger than that obtained by Graham from dilute 

 sulphuric acid by heating it to the same temperature in a vacuum 

 until it ceased to lose weight — the dihydrate, H 2 S0 4 ,'2H 2 0, remaining 

 showing the greater affinity for water possessed by the latter acid. 



Selenic acid, concentrated as above described, was poured into the 

 flask previously referred to, and gradually heated. Weak selenic acid 

 commenced to pass over at 56°, evidenced by the potash liquefying 

 and effervescing, owing to the presence of potassium carbonate which 

 it contained, being the ordinary commercial potash. It was then 

 heated slowly up to 100°, kept at that temperature so long as any acid 

 distilled over, and the strength of the residue taken : 0*9432 gram re- 

 quired for neutralisation 24*10 c.c. of seminormal soda solution, 

 equivalent to 92*44 per cent, of selenic acid. Subsequent to this 

 experiment, acids heated on various occasions to 100° were found to 

 have the following percentages of anhydrous selenic acid : — 92*03, 

 92-08, 93-28, and 9370; the different results being found due to the 

 varying conditions of the experiments, such as the length of time of 

 heating, the quantity of potash, and its proximity to the acid, the 

 amount of the latter, and the size of the flask containing it. 



The acid which had been heated to 100°, was next heated to 150°. 

 At the latter temperature the more or less dilute acid distilling over 

 appeared in the form of dense white fumes resembling those of sul- 

 phuric acid. 0'6898 gram of the residue left nentralised 18'42 c.c. of 

 seminormal soda solution, equivalent to 96*58 per cent, of selenic acid. 

 It was again heated to 150°, and kept at that temperature so long as 

 any acid distilled over : 0*417 gram of the residue left neutralised 

 11*21 c.c. of seminormal soda, equivalent to 97*25 per cent, of selenic 

 acid. 



A fresh portion of acid w r as heated, to 155° and kept for some time 

 at that temperature : 0*8045 gram of the residue neutralised 21*72 c.c. 



