486 



Mr. J. B. Hamiay. 



[June 10, 



the iodide more soluble, or did its solubility increase more rapidly 

 •with temperature, I have no doubt that its effect upon the critical 

 point "would be much more pronounced. 



By performing a large number of experiments I came to the follow- 

 ing conclusions : — 1st. The gas must have a certain density before it 

 will act as a solvent, and when its volume is increased more than twice 

 its liquid volume its solvent action is almost destroyed. 2nd. Retaining 

 the volume the same, the higher the temperature the greater the 

 solvent power. This was determined by placing an excess of iodide in 

 the tube and raising the temperature to a given point and maintaining 

 it for an hour or so, then noting portions still undissolved, raising the 

 temperature again, and watching the effect till a temperature was 

 reached when all the salt dissolved. As the increase in the solubility 

 in potassic iodide is very slight, it takes a considerable rise to have 

 any apparent effect. Thus we see that two conditions are requisite, 

 molecular closeness and vis viva. We see from this that the liquid 

 condition of fluids has very little to do with their solvent power, but 

 only indicates molecular closeness. Should this closeness be attained 

 loj external pressure instead of internal attraction, the result is that 

 the same or even greater solvent power is obtained ; greater because 

 of the greater activity of the molecules so compressed. That this is 

 the case is seen well in the case of hydrogen, which, when compressed 

 by a pressure of 1,000 atmospheres, measured by the hydrogen mano- 

 meter, dissolves potassium, sodium, and lithium. The experiment is 

 done in this way. A piece of the metal is placed in the end of the 

 tube, and the dry hydrogen below it. The pressure is then applied, and 

 after twenty or thirty minutes the mercury near the metal will be 

 found to be solid amalgam. This is at the ordinary temperature ; but 

 should the temperature be raised to 100°, the mercury becomes solid 

 in a few seconds. I intend to apply still higher pressures, and attempt 

 to dissolve harder metals. This is a case of purely gaseous solution, 

 the hydrogen being at a very great distance from its critical point. 



The conclusions arrived at in a former paper have been called 

 in question in a paper by Professor Ramsay, and I would ask 

 permission to point out some errors into which I think the author 

 has fallen. He says : — " When the tube contains a small amount of 

 liquid the space left for gas is larger, and consequently more vapour 

 must be given off by the liquid before enough gas can be compressed 

 till it acquires the same specific gravity as the liquid, the temperature 

 at which the meniscus disappears is consequently higher." * It is dim- 

 cult to understand how the author came to such a conclusion, unless 

 he was thinking of the amount of heat required to form more vapour, 

 and confounding calorimetry with thermometry. His conclusion, as it 

 stands, is at variance with all the experiments and conclusions of the 



* " Proc. Eoj. Soc," toI. xxs, page 326, lines 10 to 14. The italics are mine. 



