1880.] On the Solubility of Solids in Gases. 



185 



the solid state ? To answer this question, a solution of anhydrous 

 cobaltous chloride was sealed in a tube as before, and its spectrum 

 observed while heat was applied. No change could be detected in its 

 passage through the critical point, and a careful comparison of the 

 spectra of the same solution at 15° 0. and at 300° C. showed no differ- 

 ence beyond the fainter and more nebulous character of the bands 

 caused by expansion. The position of the bands was not changed. 

 Chloride of cobalt, however, was not well fitted for our purpose, the 

 measurement of the bands being rather uncertain on account of the 

 nebulous nature of their edges. At the suggestion of Professor Stokes, 

 we turned our attention to the product of the decomposition of chloro- 

 phyll by acids. The beautiful spectrum of a solution of this body in 

 alcohol was quite permanent, even at a temperature of 350° C, although 

 when heated in air it decomposes below 200° C. A direct comparison 

 of the hot and cold solutions failed to show any change in the position 

 of the lines. 



A good opportunity of testing the question further seemed to be 

 offered by the blue solution of sodium in liquefied ammonia, described 

 by Gore.* To prepare this, we first tried compression of the gas by 

 the pressure apparatus, but the quantity of liquid got by this method 

 was too small for experiment. We next tried a combination of Gore's 

 method with the pressure apparatus. A tube, shaped as in the draw- 

 ing, had the wide part charged with chloride of calcium saturated 

 with ammonia, and the end sealed. By applying slight heat, the air 

 was expelled by the liberated ammonia. A small piece of sodium was 

 then placed in a pocket near the end of the experimental tube, and, 

 after sealing, the tube was placed in the pressure apparatus and sur- 

 rounded with mercury. The iron tube was now heated by flaming 

 with a Bunsen, and the experimental tube cooled in a freezing 

 mixture. Distillation of ammonia commenced, and when a sufficient 

 quantity of liquid was obtained the pressure screw was advanced, 

 until, coming in contact with the wide tube, it broke the narrow neck 

 joining it with the experimental tube, and allowed the mercury to 

 rush in and enclose the liquefied ammonia. Further pressure brought 

 the ammonia in contact with the sodium and solution commenced, but 

 an unforeseen difficulty caused the experiment to fail, for the sodium 

 solution coming in contact with the mercury was rapidly decolorised 

 by it. It was, therefore, necessary to dispense with the use of mer- 

 cury. Several methods were proposed, and we finally arrived at the 

 following simple and effective one. A piece of tubing, about j inch 

 diameter, was joined to a piece of marine barometer tubing, and just 

 beside the join the latter was drawn out to an exceedingly fine bore. 

 The wide tube was now charged with ammonia-saturated chloride of 



* " Proc. Roy. Soc," vol. xxi. 



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