Stubr!>. — CoiKhictiritji of Aqueous. Solufioiift of Carbon-dioxu/e. IS 



recorded results (Journ. Chem. Soc, 77, 9) having a dilution 12-6, corre- 

 sponding to less than 2 atmospheres pressure. He worked down to very 

 great dilutions, and obtained a fairly satisfactory dissociation constant 

 under these conditions. 



The Dissociation Constant of Carbon-dioxide in Solution, Walker and 

 Cormack, 1900 (Journ. Chem. Soc, 77, 5). — These investigators worked 

 along the same lines as Knox, with apparently more elaborate pre- 

 cautions to insure accuracy. They measured the conductivity of solu- 

 tions of various concentrations, all at a temperature of 18°, the 

 pressure of COo in contact with the solutions never rising above atmo- 

 spheric. The ordinary Kohlrausch method of determining conductivity 

 was used, measurements being made with induction coil and telephone. 

 The apparatus was of glass, and great care was taken to insure abso- 

 lute insulation of electrodes, &c. Water for the experiments with a con- 

 ductivity of 0-7 X 10" in Siemens units at 18° was used, being obtained 

 bv successive distillations (1) with alkali, (2) with phosphoric acid, and 

 (3) alone, the last being conducted in chemically pure air. 



Reference is made to Pfeiffer's and Knox's experiments. The solutions 

 in Pfeiffer's experiments were prepared rmder pressure, and hence were 

 too concentrated to be of service in fixing the dissociation constant of 

 COa- (The same objection applies to the experiments described in this 

 thesis, and consequently no attempt has been made to determine the dis- 

 sociation constant.) 



Knox's dissociation constant is calculated as 0-380 x 10~", the authors' as 

 0-304 X 10^'', corresponding to a difference in actual conductivity of about 

 10 per cent. This result is considered as being due to the authors having 

 used better conductivity-water and to their more accurate method of deter- 

 mining the concentration of CO^ in the solution — viz., by titration with 

 bariums-hydroxide, as against Knox's measurement by means of the pressure 

 of CO2 in the solution. (The above-mentioned discrepancy between the 

 results of good workers would seem to show the experimental difficulty in 

 obtaining accurate results when working with very small conductivities.) 



The conductivity imparted to pure water by exposure to atmospheric 

 CO2 is calculated to be 0-65 x 10" Siemens uiiits. At this very small 

 concentration 14-4 per cent, of the dissolved COo exists in the ionized state. 



The remainder of the paper and an addendum (Journ. Chem. Soc, 83, 

 182) discusses the relative proportions of dissolved COo and un-ionized 

 H2CO3 existing in the solution, but without coming to any very definite 

 conclusion. 



A Hydrate of Carbon-dioxide, Villard, 1895 (Journ. Chem. Soc, 68, ii, 44). 

 — The author's experiments lead him to take CO26H2O as the composition 

 of the hydrate. It does not decompose below 0° (c/. with Hempel and 

 Seidel, below). 



The Absorption Coefficient of Carbon- dioxide in Water at 0°, Prytz and 

 Hoist, 1895 (Journ. Chem. Soc, 68, ii, 104). — The freezing-point of a satu- 

 rated CO2 solution at atmospheric pressure was determined, giving a depres- 

 sion of 0-156°. The calculated depression, assuming all the COj to dissolve 

 as such or as H2CO3, was 0-158°. Absorption coefficient at 0° = 1-7308. 



Compounds of Carbon-dioxide with Water, Hempel and Seidel (Journ. 

 Chem. Soc. 76, ii, 151). — By sealing solid CO2 and water in a glass tube, 

 allowing temperature to rise to ordinary temperature and then cooling, a 

 CO2 hydrate was crystallized out ; at 8° it melted under the vapour-pressure 



