Page:Transactions of the Geological Society, 1st series, vol. 1.djvu/244

 desirous, for the sake of obtaining further evidence on the subject, to bring the sulphat of alumine to a crystallized state, by artificially supplying what I conceived to be wanting for the completion of that process. For this purpose, having dissolved about thirty grains of residue in distilled water, I added to the filtered solution two or three drops of a solution of carbonat of potash, and evaporated it very slowly; crystals were thus obtained, dispersed in the saline mass, which, though of a size scarcely exceeding that of a pin's head, had a distinct octahedral form, and when separated and chemically examined, had all the properties of alum.

5. With regard to the proportion of sulphat of alumina, contained in the water, it will be seen, that by connecting together the results of the experiments just related (1, 2, 3), eighty grains of residue, or a pint of the water, yield 3,8 grains of alumine heated to redness, which, according to the proportion of twelve parts of ignited alumine, in one hundred parts of crystallized alum, would be equivalent to 31,6 grains of alum in each pint of the water.

1. Some of the former experiments (§ III. d and g) had shown, beyond all doubt, the presence of selenite, and indeed; from the general composition of the water, lime could scarcely be supposed to exist in it in any other form of combination.