On the Limit of the Liquid State. 



319 



The last liquid examined was carbon tetrachloride, and this was 

 very carefully dried and purified by fractionation and distillation off 

 quick-lime, the purified liquid being kept with the same precautions as 

 were used in the other cases. It was seen, however, that the tetra- 

 chloride acted upon the mercury, forming a white crystalline body 

 which crystallised out as the liquid cooled. It appeared to be mercuric 

 chloride, as it dissolved in water ; but whether the crystals were pure 

 mercuric chloride or a compound of that body with some other 

 chloride of carbon there was not sufficient obtained to determine. 

 The critical temperature and pressure were determined with twenty 

 different samples, using one quantity only for two or three readings, 

 and the following numbers were obtained : — 



Mean temperature corrected 282 0, 51. 



Probable error 0°'38. 



Mean pressure corrected 57*57 atmos. 



Probable error 014 „ 



On attempting to obtain the critical temperature under pressure it 

 was found that the hydrogen at once dissolved under pressure, and 

 not only dissolved, but formed a compound with the tetrachloride. 

 Some curious observations were made on the relation of pressure to 

 chemical combination with this mixture. It was found that for a 

 given temperature and pressure only a certain amount of combination 

 would take place, leaving the excess of hydrogen overlying the tetra- 

 chloride quite free. If then more pressure were applied, the mano- 

 meter would jump up say five atmospheres, and then gradually fall 

 about four or four and a half atmospheres, and again become stable, 

 and this would take place each time, a large portion of hydrogen 

 disappearing for a small permanent rise of pressure. A sudden rise 

 of temperature had somewhat the same effect, but as the temperature 

 could not be varied so suddenly the effect was not so obvious. Several 

 bodies were formed by the action of the hydrogen, the action being 

 capable of being pushed so far as to form chloroform. Nitrogen was 

 used as a pressure substance, and it answered well. The following 

 numbers were obtained from twenty-seven experiments : — 



Mean temperature corrected 277°"56. 



Probable error 0°"29. 



Mean pressure corrected 142-83 atmos. 



Probable error 0*13 ,, 



From this it will be seen that by increasing the pressure to nearly 

 three times the normal, a fall of five degrees in the critical temperature 

 has taken place. This was no doubt due to the surface tension being 



