794 Transactions. 
The formula used for the calculation of the hydrogen-ion concentration is 
E = E, + 0-059 log, С at 25° C, 
where E = E.M.F. of the element in volts, E, = 0-277 volt, © = concen- 
tration of hydrogen ions. 
en a normal calomel electrode is used as the other half-element, 
if z is the observed E.M.F., then the potential of the other element is 
(0-564 — x) volt at 25? C., 
which is E of the formula above. 
80, according to theory, the observed E.M.F. will increase with 
decrease of hydrogen-ion concentration; and, since the carbonate solutions 
are all akaline to phenolphthalein, the hydrogen-ion concentration will be 
small, and hence the observed E.M.F. will be great. 
is difference of potential may be deduced approximately as follows : 
The concentration of the calcium ions in the solution is of the order 
107 . mols. per litre. Now, assuming that the calcium exists solely 
as carbonate or the products of hydrolysis of the carbonate, the hydrogen 
10n 1$ present at about 10—10 . mols. per litre. 
Since the hydrolysis of the carbonate proceeds according to the equation 
2CaCO, + 2H,O = Ca(OH), + Ca(HCO,), 
=. 
(00, — 1°92 x 10"*, | 
whence the value of the product [Ca-] [CO,"] may be calculated. 
The E.M.F. produced was measur by th inary potentiometer 
of oxygen. The hydrogen was generated under a pressure sufficient to 
keep the gas bubbling through the solution. The solutions were filter 
rough cotton-wool out of contact with air, the first portions being 
rejected. The electrode vessel was then left in the thermostat till the 
жыз was saturated with hydrogen. 
Discussion or RESULTS. 6 
The solubility-curves obtained were not straight lines, and the deviation 
was greater than the experimental error. Apparently a new effect appears 
at about M/50, since a sudden change of direction occurs near this : 
