The solubilities of the red and yellow forms of lead monoxide, of hydrated lead monoxide and of basic lead carbonate in dilute aqueous potassium hydroxide solutions at 25°have been determined.The change of the stoichiometrical equilibrium constant with concentration shows that the activity coefficient of the plumbite ion is about the same as that of the nitrate ion in dilute solutions.From the extrapolated values of the equilibrium constants, the free energies of solution have been calculated.

3799final temperatures, a number of different determinations with different accidental reading errors are obtained in one measurement, as with the slowly changing temperatures in non-adiabatic work, and yet with the advantages of adiabatic method. The maintenance of the adiabatic condition during the slow changes of end-temperatures is very easy if the calorimeter bath is also heated electrically. Finally, it will be noted that, if the heat capacity of the calorimeter has been accurately determined, this type of measurement yields the heat of reaction directly in units of energy, the thermometer acting as an indicating instrument only-or primarily.summary This paper describes a procedure] dependent upon the precise maintenance of an adiabatic condition for a few hours, whereby the relative values of all the nominal 0.01 O or other minute marked intervals of thermometers may be determined to *0.0002° or less by a continuous process, that, namely, of the generation within the calorimeter of electrical heat a t a constant rate, precision of reading being secured by observations of the intervals of time during which the scale intervals are traversed. The accuracy of the method is demonstrated by data on the calibration of calorimetric mercury thermometers, and on errors of measurement which are briefly discussed.The method is presented as the essential basis of a procedure for the complete standardization of calorimetric mercury thermometers.Its direct: applicability to thermochemical measurement is briefly discussed. NEW YORK CITY