634 I'HILOSOPHICAL TRANSACTIONS. [anNO I769. 



is soluble in simple water, by the intervention of fixed air; and thence, that it 

 is very probable, many different chalybeate springs sustain their metallic charge 

 by this means only. 



The solution of iron in mineral waters, especially in such as, by exposure, 

 readily lose the property of striking a purple colour with astringent vegetables, 

 has usually been attributed to some subtile gas, or volatile acid. Chemistry 

 however does not discover any acid solvent for iron, but what has greater affinity 

 with alkalies; and by means of which therefore this metal will be precipitated. 

 Hence if any water appears, with a predominant alkali, which has also the power 

 of tinging with galls, and, on being exposed to the open air, lets fall the iron, 

 and loses that property; may we not conclude the metal to have been suspended 

 by some other medium ? This, for example, is plainly the case in German spa 

 water, which Dr. Brownrigg has proved to abound with fixed air. Mr. Caven- 

 dish's very curious experiments, before cited, clearly showed, that calcarious 

 earths might be suspended in water by this principle of fixed air. And these 

 had led Mr. L. to examine, whether iron might not be dissolved by the same 

 natural means. 



He would not however be supposed to deny, that iron is frequently found 

 united vi'ith an acid. The fact is sufficiently evinced in the pyrites and vitriolic 

 earths. Nor could he doubt, but that these substances do largely contribute to 

 the primary impregnation of waters, they being so readily soluble in theni. But 

 as an alkali, or absorbent earth, is often found more than sufficient to , saturate 

 the acid in mineral waters; this would effectually disengage every particle dissolved 

 by an acid, unless the metal was supported by some other menstruum. His 

 endeavours therefore to detect this solvent, by experiments, are what he here 

 offers. 



Exper. 1. — A wide-mouthed bottle, containing -i- a pint of distilled water 

 and 60 grs. of steel filings, was suspended 48 hours over some distillers melasses, 

 in brisk fermentation; so as to receive the fixed air escaping from the fermenting 

 liquor; the surface of which was 10 inches below the mouth of the bottle. 

 Immediately after its removal, the clear water was decanted from the filings and 

 ochrous sediment. This liquor had a brisk and ferruginous taste, with a flavour 

 of the melasses. An infusion of galls, or green tea, soon changed part of it to 

 a colour like ink. The remainder, being exposed to the open air, presently 

 became turbid, threw up a party-coloured pellicle, and deposited a yellowish 

 sediment. The water now retained but very little power of tinging with galls; 

 and in a few days lost this property entirely. 



Exper. 1. — Fourteen oz. of coarse sugar, dissolved in 7 pints of water, were 

 mixed with 4- a pint of yeast, in a bottle capable of holding more than twide the 



