Page:Transactions of the Geological Society, 1st series, vol. 1.djvu/241

 carefully washed, dried, and ultimately heated to redness with a little wax in a platina crucible, weighed 7,2 grs.

3. It will be observed that between this and the former result there was a difference of 0,4 grs. in the quantity of oxyd of iron contained in 50 grs. of residue. But when it is considered that in the first of these analyses, a small quantity of iron was positively detected in the acetic solution, which, from the best estimate I could make, would have brought the quantity of iron very near that obtained in the second process, it will readily be admitted that the coincidence was such as to authorize me to consider the last result as sufficiently accurate.

4. If therefore we consider 7,2 grs. of peroxyd of iron, as the quantity of this metal contained in 50 grs. of the residue, which corresponds to 11,59 grs. of the oxyd for 80,5 grs. of residue (that is for each pint of the water, according to the average before established, § VI. 2), we shall be able to infer the quantity of sulphat of iron contained in the water.

5. In order to do this, however, it was necessary to ascertain by a comparative experiment the proportion of oxyd which a known quantity of sulphat of iron yields by a process similar to that which I have just described. For this purpose, 50 grs. of transparent crystallized green sulphat of iron were dissolved in water, and treated with carbonat of ammonia as long as any precipitate appeared.