The Guldberg-Waage curve at 100° was also determined, and it was found that the ratio K2CO3: K2SO4 is also not constant, although the variations are not so great as at 25°.
Guldberg-Waage Curve at 100°.
| Solid phases. | 100 moles of water contain, in moles, | Σk2 | K2CO3 K2SO4 | |
| K2CO3 | K2SO4 | |||
| BaCO3 + K2SO4 + BaSO4 | 23.9 | 12.65 | 35.65 | 1.82 |
| BaCO3 + BaSO4 | 6.28 | 2.02 | 8.3 | 3.1 |
| " " | 3.17 | 0.851 | 4.025 | 3.7 |
APPENDIX
EXPERIMENTAL DETERMINATION OF THE TRANSITION POINT
For the purpose of determining the transition temperature, a number of methods have been employed, and the most important of these will be briefly described here. In any given case it is sometimes possible to employ more than one method, but all are not equally suitable, and the values of the transition point obtained by the different methods are not always identical. Indeed, a difference of several degrees in the value found may quite well occur.[[398]] In each case, therefore, some care must be taken to select the method most suitable for the purpose.
I. The Dilatometric Method.—Since, in the majority of cases, transformation at the transition point is accompanied by an appreciable change of volume, it is only necessary to ascertain the temperature at which this change of volume occurs, in order to determine the transition point. For this purpose the dilatometer is employed, an apparatus which consists of a bulb with capillary tube attached, and which constitutes a sort of large thermometer (Fig. 129). Some of the substance to be examined is passed into the bulb A through the tube B, which is then sealed off. The rest of the bulb and a small portion of the capillary tube is then filled with some liquid, which, of course, must be without chemical action on the substance under investigation. A liquid, however, may be employed which dissolves the substance, for, as we have seen (p. [70]), the transformation at the transition point is, as a rule, accelerated by the presence of a solvent. On the other hand, the liquid must not dissolve in the substance under examination, for the temperature of transformation would be thereby altered.