636 PHILOSOPHICAL TKANSACTIONS. [aNNO I769. 



a purple, as in common solutions of iron. The liquor, decanted after boiling, 

 ■neither changed colour with galls, nor showed any precipitation with lime-water. 



Exp. 3. A common quart bottle was half filled with distilled water, to which 

 were added 100 grs. of steel filings. To these was introduced, by means of the 

 bent tube, as much fixed air, obtained from a solution of alkaline salt in the 

 vitriolic acid, as was judged sufficient to fill the bottle. The whole being then 

 shaken, with his hand over its mouth, the bottle stuck like a cupping-glass. 

 About the same quantity of air being again added, the bottle, after shaking, had 

 less adhesion than before. On repeating this experiment, a third time, with 

 fresh air, the adhesion was scarcely perceptible. And after the 4th trial, a small 

 portion of air was observed to issue from the bottle. The water now gave a deep 

 colour with tincture of galls. This experiment was repeated with fixed air from 

 different combinations: as also by passing this air through a vessel of pearl-ash, 

 to arrest any acid which might escape from the effervescing mixtures: but the 

 solutions of iron, in all the trials, appeared to be exactly similar, except some 

 trifling difference in taste and smell. 



Exp. 4. A bottle, with the like quantity of steel-filings and distilled water as 

 in the first experiment, remained in a room many weeks; yet though it was fre- 

 quently shaken, and had an ochrous sediment, it gave no colour with tincture 

 of galls. 



Exp. 5. A single grain of iron in solution,* diluted with a pint of distilled 

 water, changed to a deep blue purple, with the tincture of galls. Half a pint 

 of the like mixture*" exposed many days in a wide-mouthed glass covered loosely 

 with paper, let fall a slight precipitation; but its property of tinging with galls 

 was not sensibly diminished. The same quantity being boiled 4 or 5 minutes in 

 a Florence flask, became turbid, and deposited a small portion of an ochrous 

 sediment. Yet the tincture of galls gave as deep a colour to the clear liquor as 

 it would have done before boiling. 



The foregoing experiments seem to prove, that iron remains quite unaffected 

 by pure water, but may easily be dissolved in it on the addition of fixed air; and 

 that in whatever manner this air is generated, the event will appear the same. 

 The last experiment shows, that where iron is suspended in water, by an acid, 

 neither exposure nor boiling will destroy its property of tinging with galls ; which 

 is the reverse of what we find to be the case with many ferruginous waters. The 

 2d experiment more particularly teaches, that the iron, ' dissolved in water by 

 fixed air, is at least equal in quantity to what is commonly ascribed to most cha- 

 lybeate springs: that this air, by which the metal is held in solution, is similar 



• Iron-filings were dissolved in diluted oil of vitriol to saturation; and by experiment, one grain 

 of the metal, with about 2| grs, of the acid, were found to be contained in 6'8 grs. of the solution. 

 — Orig. 



