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Messrs. J. B. Hannay and J. Hogarth. [Feb. 26,. 



solution to be tested, and by a few experiments the strength of the- 

 solution was so adjusted that no separation of solid took place, when 

 the tube was completely filled by expansion. 



The behaviour of a solution of potassic iodide we have already 

 described. Bromide of potassium gave a similar result. The solubility 

 of chloride of calcium in alcohol was found to be uninterrupted by the- 

 passage of the alcohol through the critical state. Cobaltous chloride 

 (anhydrous) remained in solution at 320° C. the highest temperature 

 reached in this experiment, and the beautiful blue colour of the 

 solution was unimpaired. Ferric chloride (sublimed) gave a yellow 

 fluid at a temperature of 260° C. This yellow colour rapidly disap- 

 peared, and a reddish- coloured powder separated out, which remained 

 insoluble on cooling. On opening the tube a strong ethereal odour 

 was perceived. This was most probably due to the formation of ethylic 

 chloride. Some peculiar phenomena observed when heating the ferric 

 chloride solution deserve description. At a temperature of 120° C. a 

 very strongly coloured liquid layer appeared at the bottom of the tube, 

 while the uppermost layer was perceptibly paler. As the temperature 

 rose the two layers gradually mixed and the fluid was quite homo- 

 geneous at and above the critical point. 



A solution of ferric chloride in ether was distinctly coloured at least 

 30° C. above the critical point, but the colour gradually faded, and 

 did not return on cooling. The separation and redissolving of part of 

 the ferric chloride occurred also with ether. 



A solution of sulphur in carbon disulphide showed no separation 

 of sulphur when raised 50° C. above its critical point. Of course 

 sulphur at this temperature is a liquid, but its vapour tension is com- 

 paratively so small that its solution is worth recording. Selenium also 

 remained in solution in carbon disulphide above its critical point, and 

 separated out in part when the solution coolei. Chemical action 

 evidently took place in this experiment, for on evaporating a portion 

 of the solution after heating, a reddish-yellow residue containing* 

 selenium was obtained. The liquid had a distinct horse-radish smell, 

 and on burning gave a dark stain on a piece of porcelain held in the 

 flame. Sulphide of selenium was most probably formed. An attempt 

 was made to dissolve cadmic sulphide in carbon disulphide, but 

 without success. In an experiment with metallic arsenic and carbon 

 disulphide the arsenic seemed to dissolve, but as an orange-coloured 

 film appeared on the glass on cooling, we are inclined to doubt its 

 solubility. When some sulphur was enclosed in the tube with arsenic 

 and carbon disulphide, and the temperature raised above the critical 

 point, solution occurred, and when the temperature was allowed to 

 fall a separation of dense liquid drops took place at the critical point. 

 At a lower temperature these solidify and form reddish-yellow r crystals. 

 The apparent solubility of arsenic was thus probably due to its con- 



