232 Dr. Marcet on an Aluminous Chalybeate Spring 



desirous, for the sake of obtaining further evidence on the subject, 

 to bring the sulphat of alumine to a crystalUzed 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 octohedral form, and when separated and chemically exa- 

 mined, had all the properties of alum. 



5. With regard to the proportion of sulphat of alumine, 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 alumf , would be equivalent to 

 31,6 grains of alum in each pint of the w^aterj:. 



§ X. Sulphat of Lime. 



1. Some of the former experiments (§ III. d and g) had shown, 

 beyond all doubt, the presence of selenite, and indeed, from the ge- 

 neral composition of the water, lime could scarcely be supposed to 

 exist in it in any other form of combination. 



* These arc the proportions stated by INIr. Kirwan, and which I obtained myself on a 

 former occasion (See the Analysis of the Brighton Chalybeate.^ 



* It is scarcely necessary again to observe, that the sulphat of alumine contained iu 

 the water does not appear to exist there in the state of alum ; but it is perhaps better to 

 express the quantity of alumine by the quantity of alum which it would form, as the 

 crystallized state of a salt affonls a much more precise standard of comparison. 



