From some of the above experiments, it appears, that a few alterations may be made in the column of acids in Mr. Geoffroy's table of elective attractions, and that a new column may be added to that table, according to the following scheme, where the alkaline substances are all considered as in their pure state and free of fixed air.
| Acids. | Fixed air. | |
| Fixed alkali | Calcarious earth. | |
| Calcarious earth, | Fixed alkali. | |
| Volatile alkali and magnesia. | Magnesia. | |
| Volatile alkali. | ||
At the foot of the first column several of the metals might follow, and after these the earth of alum; but as I don't know what number of the metals should precede that earth, I have left it to be determined by further experience.
The volatile alkali and magnesia are placed in the same line of this column; because their force of attraction seems pretty equal. When we commit a mixture of magnesia and salt ammoniac to distillation, the alkali arises and leaves the acid with the magnesia; because this earth, by attracting the acid, represses its volatility, and it seems also to diminish the cohesion of the acid and alkali, and to render them separable by a gentle heat. If the magnesia be saturated with air, this likewise, on account of its volatile nature and attraction for the alkali, is driven up along with it, and makes it appear under a mild form, and in the same manner do the alkali and air arise from a mixture of salt ammoniac and of a crude calcarious earth.
Footnotes:
[1] June 5. 1755.
[2] Hoff. Op. T. iv. p. 479.
[3] Hoff. Op. T. iv. p. 500.
[4] Mr. Margraaf has lately demonstrated, by a set of curious and accurate experiments, that this powder is of the nature, and possesses the properties, of the gypseous or selenitic substances. That such substances can be resolved into vitriolic acid and calcarious earth, and can be again composed by joining these two ingredients together. Mem. de l'Acad. de Berlin. an. 1750, p. 144.
[5] Hoff. Op. T. iv. p. 480 & 500.