wis PHILOSOPHICAL TRANSACTIONS. [aNNO 176Q. 



Jjart of the iron would remain in the water after boiling. All which were disco- 

 verable by the tincture of galls. 



Exp. 8. To a pint of distilled water, being saturated with fixed air, and con- 

 taining 4 grs. of chalk, was added 1 gr, of iron in solution ; the mixture con- 

 tinued pellucid. ' '-"• ' '■ '' -'■ -i^i..- ,i;,;-.ill :^.:> ■.,.i._.i, ,r I, r<.U ,tiii i: 



Another grain of dissolved iron was diluted with a like quaritity of water, 

 previously saturated with air from a solution of pearl-ash in vitriolic acid; 8 grs. 

 of salt of tartar, crystallized with fixed air, and dissolved, were added to this 

 mixture: a slight degree of cloudiness ensued, but disappeared on shaking; after 

 which the liquor- much resembled spa- water; only it tasted stronger of the iron; 

 The quantity of chalk, and of alkaline salt, in this experiment, was more than 

 sufficient to neutralize the acid. 



Both the above mixtures, on exposure, became turbid, threw up pellicles, de- 

 posited ferruginous sediments, and lost their power of striking a purple with galls. 



Solutions of iron, and qf its ores, in the marine and nitrous acids, as also 

 pyrites dissolved in rain water, were substituted, by turns, instead of the original 

 iron in vitriolic acid; and they all gave a purple colour with tincture of galls. 



The trials were repeated with lime-stone, marble, island crystal, osteocolla, 

 and magnesia, instead of chalk; and with volatile and mineral alkali, replete 

 with air, instead of salt of tartar; but no material difference was observed. 



The success of these experiments completely answered his expectations. They 

 feiatisfied him, that any acid holding iron dissolved, and diluted with water, might 

 hot only be neutralized, but the water charged with an excess of alkaline or 

 earthy matter, without precipitating the metal; and that the solvent, in these 

 cases, could be no other than fixed air. Since the iron remained in solution, 

 Only where this principle originally abounded in the water, or was afterwards 

 generated in the saturation. 



Thus much being determined, it seemed easy to apply the discovery to the 

 more perfect analyzation of some waters ; and to the re-production of others, by 

 art, which should exactly resemble those of natural medicated springs. This is 

 a task he should probably have undertaken at leisure ; had he not been informed, 

 that Dr. Watson, junior, by whose conversation his thoughts were first led to 

 the subject, was then engaged in something of this sort. This gentleman saw 

 "many of the foregoing experiments repeated; and, as he afterwards went to the 

 German spa, his abilities and application would sufficiently improve the oppor- 

 tunity : he should gladly therefore wait the result of his inquiries. 



To conclude, it appeared to Mr. L. highly probable, that fixed air is generally 

 necessary to the impregnation of mineral springs. That by the right knowledge 

 of this principle, we might now solve most difficulties that had arisen on this 



