1880.] 



On the Solubility of Solids in Gases. 



187 



lead oxide, due to the action of hydrogen on the hot glass, makes the 

 demonstration of the solubility of sodium in hydrogen exceedingly 

 difficult, but the phenomena described, we are convinced, can only be 

 explained on this hypothesis. In several experiments we have seen 

 little pieces of sodium slowly disappear, leaving only the thin shell of 

 oxide formed round them while they were being placed in the tube. 

 There seemed in many cases to be a sudden chemical action, for the 

 tube burst, not while pressure was being applied, but often several 

 minutes after the pressure screw had been advanced. A beam of 

 light passed through the tube showed no absorption when examined 

 by the spectroscope. 



Having described our experiments, it remains only for us to con- 

 sider the state of the solvent at a distance above the critical point. 

 We cannot do better than quote Dr. Andrews' consideration of the ' 

 subject. He says,* "What is the condition of carbonic acid when it 

 passes at temperatures above 31° C. from the gaseous state down to 

 the volume of the liquid without giving evidence at any part of the 

 process of liquefaction having occurred ? Does it continue in the 

 gaseous state, or does it liquefy, or have we to deal with a new con- 

 dition of matter ? If the experiment were made at 100° C, or at a 

 higher temperature, when all indications of a fall had disappeared, the 

 probable answer that would be given to this question is, that the gas 

 preserves its gaseous condition during the compression, and few would 

 hesitate to declare this statement to be true, if the pressures, as in 

 batterer's experiments, were applied to such gases as hydrogen or 

 nitrogen. On the other hand, when the experiment is made with 

 carbonic acid at temperatures a little above 31° C, the great fall 

 which occurs at one period of the process would lead to the conjecture 

 that liquefaction had actually taken place, although optical tests care- 

 fully applied failed at any time to discover the presence of a liquid in 

 contact with a gas. But against this view it may be urged with great 

 force, that the fact of additional pressure being always required for a 

 further diminution of volume, is opposed to the known laws which 

 hold in the change of bodies from the gaseous to the liquid state. 

 Besides, the higher the temperature at which the gas is compressed the 

 less the fall becomes, and at last it disappears." Leaviug out of con- 

 sideration the solubility of sodium in hydrogen, we have had iodide of 

 potassium in solution in alcohol at temperatures much too high for 

 measurement by the mercurial thermometer, and which may safely be 

 estimated at 150° C. above the critical point ( = 380° C). We think 

 therefore we are justified in saying that at this high temperature the 

 solvent was truly gaseous. An examination of Dr. Andrews' curves 

 for carbonic acid shows us that at a temperature only 16° C. above the 



* "Phil. Trans.," 1869, p. 575. 



