BODIES GENERALLY EXISTING AS GASES. 167 



When in the solid state it gives off so little vapour that the eye is not sensible of 

 its presence by any degree of colour in the air over it when looking down a tube 

 four inches in length, at the bottom of which is the substance. Hence the pressure 

 of its vapour at that temperature must be very small. 



Some hours after, wishing to solidify the same portion of euchlorine which was 

 then in a liquid state, I placed the tube in a bath at —110°, but could not succeed 

 either by continuance of the tube in the bath, or shaking the fluid in the tube, or 

 opening the tube to allow the full pressure of the atmosphere ; but when the liquid 

 euchlorine was touched by a platinum wire it instantly became solid, and exhibited 

 all the properties before described. There are many similar instances amongst ordi- 

 nary substances, but the effect in this case makes me hesitate in concluding that 

 all the gases which as yet have refused to solidify at temperatures as low as 166° 

 below 0°, cannot acquire the solid state at such a temperature. 



Nitrous oxide. — This substance was obtained solid by the temperature of the car- 

 bonic acid bath in vacuo, and appeared as a beautiful clear crystalline colourless body. 

 The temperature required for this effect must have been very nearly the lowest, per- 

 haps about 150° below 0°. The pressure of the vapour rising from the solid nitrous 

 oxide was less than one atmosphere. 



Hence it was concluded that liquid nitrous oxide could not freeze itself by evapo- 

 ration at one atmosphere, as carbonic acid does ; and this was found to be true, for 

 when a tube containing much liquid was freely opened, so as to allow evaporation 

 down to one atmosphere, the liquid boiled and cooled itself, but remained a liquid. 

 The cold produced by the evaporation was very great, and this was shown by putting 

 the part of the tube containing the liquid nitrous oxide, into a cold bath of carbonic 

 acid, for the latter was like a hot bath to the former, and instantly made it boil 

 rapidly. 



I kept this substance for some weeks in a tube closed by stop-cocks and cemented 

 caps. In that time there was no action on the bitumen of the graduation, nor on 

 the cement of the caps ; these bodies remained perfectly unaltered. 



Hence it is probable that this substance may be used in certain cases, instead of 

 carbonic acid, to produce degrees of cold far below those which the latter body can 

 supply. Down to a certain temperature, that of its solidification, it would not even 

 require ether to give contact, and below that temperature it could easily be used 

 mingled with ether ; its vapour would do no harm to an air-pump, and there is no 

 doubt that the substance placed in vacuo would acquire a temperature lower than any 

 as yet known, perhaps as far below the carbonic acid bath in vacuo as that is below 

 the same bath in air. 



This substance, like olefiant gas, gave very uncertain results at different times as 

 to the pressure of its vapour ; results which can only be accounted for by supposing 

 that there are two different bodies present, soluble in each other, but differing in the 

 elasticity of their vapour. Four different portions gave at the same temperature. 



