326 



Mr. C. Tomlinson on the Action of Nuclei. [Nov. 20, 



f ul directions so kindly furnished ns by Professor Stokes, and find that 

 it shows the phenomenon in a marked manner, whether dissolved in 

 alcohol or ether. The compound is easily decomposed by heat under 

 ordinary circumstances, and yet can be dissolved in gaseous menstrua, 

 and raised to a temperature of 350° without suffering any decomposi- 

 tion, showing the same absorption spectrum at that elevated tempera- 

 ture as at 15°. 



We considered that it would be most interesting to examine by 

 this method a body such as sodium, which, besides being an element, 

 yields in the gaseous state sharp absorption lines. An opportunity 

 seemed to be afforded by the blue solution of sodium in liquefied 

 ammonia, described by Gore, # but we found that, on raising the 

 ammonia above its critical point, the sodium combined with some con- 

 stituent of the gas, forming a white solid, and yielding a permanent 

 gas, probably hydrogen. 



There seems, in some cases, to be a slight shifting of the absorption 

 bands towards the red, as the temperature rises, but we have as yet 

 been able to make no accurate measurements. 



When the solid is precipitated by suddenly reducing the pressure, it 

 is crystalline, and may be brought down as a " snow " in the gas, or on 

 the glass as a " frost," but it is always easily redissolved by the gas 

 on increasing the pressure. These phenomena are seen to the best 

 advantage by a solution of potassic iodide in absolute alcohol. 



We have, then, the phenomenon of a solid with no measurable 

 gaseous pressure, dissolving in a gas, and not being affected by the 

 passage of its menstruum through the critical point to the liquid state, 

 showing it to be a true case of gaseous solution of a solid. 



VII. " On the Action of Nuclei in producing the Sudden Solidi- 

 fication of Supersaturated Solutions of Glauber's Salt." 

 By Chaeles Tomlinson, F.R.S. Received October 6, 

 1879. 



I propose now to state the general conclusions at which I have 

 arrived since resuming the study of this subject two years ago.f The 

 remarks that will be made refer to solutions of the typical salt, sodic 

 sulphate, in the proportions of 6 of salt to 3 of water. 



In my first two papers on supersaturated saline solutions, % a nucleus 

 is defined as a body that has a stronger adhesion for the salt, or for 

 the liquid of a solution, than subsists between the salt and the liquid. 



# « p roc> Roy. Soc," yoI. xxi, p. 145. 

 + " Proc. Roy. Soc," vol. xxvi, p. 523. 

 X " Phil. Trans.," 1868 and 1871. 



