162 DR. FARADAY ON THE LIQUEFACTION AND SOLIDIFICATION OF 



solid, transparent, crystalline body. It does not freeze until reduced much lower 

 than this temperature ; but being frozen by the carbonic acid bath in vacuo, it re- 

 mains a solid until the temperature in rising attains to —124°. 



Fluosilicon. — I found that this substance in the gaseous state might be brought 

 in contact with the oil and metal of the pumps, without causing injury to them, for 

 a time sufficiently long to apply the joint process of condensation already described. 

 The substance liquefied under a pressure of about nine atmospheres at the lowest tem- 

 perature, or at 160° below 0°; and was then clear, transparent, colourless, and very 

 fluid like hot ether. It did not solidify at any temperature to which I could submit 

 it. I was able to preserve it in the tube until the next day. Some leakage had then 

 taken place (for it ultimately acted on the lubricating fat of the stop-cock), and there 

 was no liquid in the tube at comqion temperatures ; but when the bend of the tube 

 was cooled to 32° by a little ice, fluid appeared : a bath of ice and salt caused a still 

 more abundant condensation. The pressure appeared then to be above thirty at- 

 mospheres, but the motion of the mercury in the gauge had become obstructed through 

 the action of the fluosilicon, and no confidence could be reposed in its indications. 



Phosphuretted /n/droge?i. —This gas was prepared by boiling phosphorus in a strong 

 pure solution of caustic potassa, and the gas was preserved over water in a dark room 

 for several days to cause the deposition of any mere vapour of phosphorus which it 

 might contain. It was then subjected to high pressure in a tube cooled by a carbonic 

 acid bath, which had itself been cooled under the receiver of the air-pump. The gas 

 in its way to the pumps passed through a long spiral of thin narrow glass tube im- 

 mersed in a mixture of ice and salt at 0°, to remove as much water from it as possible. 



By these means the phosphuretted hydrogen was liquefied ; for a pure, clear, colour- 

 less, transparent and very limpid fluid appeared, which could not be solidified by any 

 temperature applied, and which when the pressure was taken oflf immediately rose 

 again in the form of gas. Still the whole of the gas was not condensable into this 

 fluid. By working the pumps the pressure would rise up to twenty-five atmospheres 

 at this very low temperature, and yet at the pressure of two or three atmospheres and 

 ^ the same temperature, liquid would remain. There can be no doubt that phosphu- 

 retted hydrogen condensed, but neither can there be a doubt that some other gas, 

 not so condensable, was also present, which perhaps may be either another phosphu- 

 retted hydrogen or hydrogen itself. 



Fluohoron. — This substance was prepared from fluor spar, fused boracic acid and 

 strong sulphuric acid, in a tube generator such as that already described, and con- 

 ducted into a condensing tube under the generating pressure. The ordinary car- 

 bonic acid bath did not condense it, but the application of one cooled under the air- 

 pump caused its liquefaction, and fluoboron then appeared as a very limpid, colour- 

 less, clear fluid, showing no signs of solidification, but when at the lowest tempe- 

 rature mobile as hot ether. When the pressure was taken oft', or the temperature 

 raised, it returned into the state of gas. 



