184 Mr. Faraday on neiv Compounds 



190° will deposit crystals on cooling; that is to sa^', before 

 sufficient of the permanently fluid part at low temperatures 

 has been removed, to leave a solution so saturated as to cry- 

 stallize at 0°. 



Bi-carburet of hydrogen appears in common circumstances 

 as a colourless transparent liquid, having an odour resembling 

 that of oil gas, and partaking also of that of almonds. Its 

 specific gravity is nearly 0-85 at 60^ When cooled to about 

 32° it crystallizes, becoming solid ; and the portions which 

 are on the sides of the glass exhibit dendritical forms. By 

 leaving tubes containmg thin solid films of it in ice-cold water, 

 and allowing the temperature to rise slowly, its fusing point 

 w^as found to be very nearly 42° F. ; but when liquid it may, 

 like water and some saline solutions, be cooled much below 

 that point before any part becomes solid. It contracts very 

 much on congealing, 9 parts in bulk becoming 8 very nearly; 

 hence its si)ecific gravity hi that state is about 0'956. At 0° 

 it appears as a white or transparent substance, brittle, pul- 

 verulent, and of the hardness nearly of loaf-sugar. 



It evaporates entirely when exposed to the air. Its boiling 

 point in contact with glass is 186°. The specific gravity of 

 its vapour, corrected to a temperature of 60°, is nearly 40, 

 hydrogen being 1 ; for 2"3 grains became 3*52 cubic inches 

 of vapour at 212°. Barometer 29-98. Other experiments 

 gave a mean approaching very closely to this result. 



It does not conduct electricity. 



This substance is very slightly soluble in water; very so- 

 luble in fixed and volatile oils, in aether, alcohol, &c. ; the 

 alcoholic solution being precipitated by water. It burns 

 with a bright flame and much smoke. When admitted to 

 oxygen gas, so much vapour rises as to make a powerfully 

 detonating mixture. When passed through a red-hot tube 

 it gradually deposits carbon, yielding carburetted hydrogen 

 gas. 



Chlorine introduced to the substance in a retort exerted 

 but little action imtil placed in sun-light, when dense fumes 

 were formed, without the evolution of much heat; and ulti- 

 mately much muriatic acid was produced, and two other sub- 

 stances, one a solid crystalline body, the other a dense thick 

 fluid. It was found by further examination, that neither of 

 these were soluble in water; that both were soluble in alco- 

 hol — the liquid readily, the solid with more difficulty. Both 

 of them appeared to be triple compounds of chlorine, carbon, 

 and hydrogen ; — but I reserve the consideration of these, and 

 of other similar compounds, to another opportunity. 



Iodine appears to exert no action upon the substance in 



several 



