Faraday to Charles Brand¹   2 June 1828

Royal Institution | June 2d, 1828.

Sir,

I have at last been able to fine time to complete an examination of the water from the Inca’s bridge which you gave into my hands; and though I have no doubt, from the nature of the water, that it had undergone changes since you removed it from its source, (as was indeed sufficiently evident from the deposition in it of black hydrosulphuret of iron,) it still was very curious in its natural characters.

The water is distinguished, in the first place, by a large quantity of sulphureted hydrogen, which it holds in solution; this renders it fetid, and very nauseous to the taste. It has at one time also been distinguished as chalybeate, holding iron in solution, but at present al[l] the iron is separated in the form above described.

The water holds excess of carbonic acid in solution and by means of it, a large quantity of carbonate of lime is also dissolved.

Upon dissipating the carbonic acid, the carbonate of lime falls in abundance. I conclude that at the springs the water contained more carbonic acid than even that you gave me, and that the iron was formerly held in solution by it. Besides these substances, the water contains a large proportion of common salt, and also a considerable proportion of sulphate of lime; but there are no traces of magnesium salts.

The water was clear at first, with the exception of the small black flocculi; being filtered, its specific gravity was 1014.33 at 60º Fahrenheit; and ten cubical inches of it were found to yield forty-five grains of dry saline matter, of which, far the largest proportion was common salt².

I am, Sir, | Your obedient servant, | (signed) M. Faraday.

Lieut. Charles Brand, R.N. | &c. &c. &c.