Page:Transactions of the Geological Society, 1st series, vol. 1.djvu/242

This page has been proofread, but needs to be validated.

This precipitate, after being carefully separated, edulcorated, dried, and ultimately heated to redness with wax in a platina crucible, weighed exactly 14 grs. It appeared in the form of a red-brown magnetic powder.[1]

6. Since therefore 50 grs. of crystallized green sulphat of iron gave 14 grs. of this oxyd, the 7,2 grs. of oxyd obtained from 50 grs. of residue, would represent 25,7 grs. of green sulphat of iron; and 11,59 grs. of oxyd (which is the quantity contained in an English pint of the water), would represent 41,4 grs. of that salt.

§ IX. Sulphat of Alumine.

1. Fifty grains of residue [2] were boiled in two successive lixivia of caustic potash (as in § VIII. 1), so as to take up all the alumine present ; the residue was separated and well washed, and the washings were added to the alkaline solution. The clear liquor had a brownish colour, and on being tried with muriatic acid and prussiat of potash, a blue tinge was produced, which appeared to have arisen from a few particles of oxyd of iron which were suspended

  1. This result which was obtained in two different trials, with the variation of only 0,1 gr. corresponds exactly with the proportions given by Mr. Kirwan in his treatise on mineral waters (table iv.), in which 28 grs. is the quantity of oxyd stated to exist in 100 grs. of green sulphat. But in order to establish the perfect coincidence of these results, it would be necessary to know the process which Mr. Kirwan followed. The iron in his experiment, is stated to have been obtained in the state of black oxyd.
  2. These fifty grains had been previously boiled in neutral carbonat of ammonia, in order to separate the magnesia as will be detailed hereafter. The previous intervention of a carbonated alkali renders the subsequent application of caustic potash for the separation of the alumine, more unexceptionable, as a solution of caustic potash might redissolve a small portion of the lime, if it were not previously carbonated.