Stubbs. — Condiictivitii of Aqueous Sohifioiix of Cdrhou-fJioxidr . 25 



(c.) The conductivity of the hydrate-bearing solution, as has been stated, 

 is less than that of the corresponding free solution, but it increases more 

 rapidly than that solution in conductivity as the temperature is increased, 

 eventually becoming ec][ual to it in conductivity at some definite temperature 

 (varying in the experiments performed from about 6^ at 15 atmospheres 

 to 8° at 25 atmospheres pressure). Henceforward the conductivity follows, 

 the conductivity-temperature law of the ordinary solution. 



The similarity between the curve which expresses this behaviour and 

 the vapour-pressure curves of ice and water intersecting at the transition- 

 point is suggestive. Just as water can be supercooled, and its vapour- 

 pressure curve produced below 0°, so the COj solution seems capable of 

 supercooling and the solution temperature-conductivity curve can be pro- 

 duced below the true transition-point. 



{d.) As far as such evidence as was obtained can be relied on, in con- 

 formity with the statements in (6) above, the crystallization-point seems 

 to ocf ur at a lower temperature the lower the pressure : thus, at 25 atmo- 

 spheres the formation of the hydrate took place at 2°, at 20 atmospheres 

 pressure at 0°. 



(e.) A hydrate formed at one pressure can be preserved at a lower pres- 

 sure if the temperature be kept low ; but when it melts, which it does at a 

 definite temperature, it does so completely and rapidly, causing a sudden 

 rise in the conductivity and increase in the pressure, due to evolution of 

 the extra CO2 held. The melting-point rises in such cases with increase 

 of concentration : thus, the hydrate formed at 20 atmospheres and decom- 

 posed at 15 atmospheres melted at 3°, while that formed at 25 atmospheres 

 and decomposed at 20 atmosj)heres melted at 5|°. This behaviour agrees 

 fairly well with the observations of Hempel and Seidel, who found that the 

 hydrate formed by them at a very high pressure — i.e., the vapour-pressure 

 of liquid COo — melted under this pressure at 8° and under atmospheric pres- 

 sure at — 2°. 



(/.) At 0° C. the hydrate is decomposed at between 8 and 10 atmospheres 

 pressure. 



{g.) Wroblewski's statement that the hydrate is " capable of existing 

 only under certain pressures, increasing with the temperature," is inaccurate, 

 as the hydrate has been formed or kept in existence at 0° under pressures 

 varying from 9 or 10 to 30 atmospheres. There is apparently a lower 

 pressure-limit, but not a higher. 



(h.) It seems certain from the facts mentioned in (e) that the composi- 

 tion of what has been styled " the hydrate " varies. There was no means 

 of determining, however, whether more than one hydrate M-as formed. 



