Faraday to John Barrow¹   9 September 1834

Royal Institution, 9th September, 1834.

Dear Sir, - I have been engaged in examining the water you sent me from the Geyser, but found myself sadly limited by the smallness of the quantity; there was not more than six ounces of it altogether.

This water had none of the smell of sulphur of which you spoke, nor could I find any traces of deposited sulphur, neither had it deposited any thing apparently since you put it in the bottle; it had a little colour, but I suspect that was derived from the cork.

The water is distinguished, even in its present state, from other waters, by containing a peculiar combination of silica and the alkali, soda. When the water is evaporated, this compound is in part decomposed, the silica deposited in an insoluble state, the alkali is set free, being probably assisted in this change by the carbonic acid of the atmosphere, and being dissolved in, and removed by, water, is found in considerable abundance.

The silica which is thus deposited is not merely insoluble in water, but in sulphuric, nitric, or muriatic acid also, and quite resembles the purer parts of that which you sent me as deposited at the spring. The alkali is in such quantity, that when washed from the silica by distilled water before evaporation, it readily affects turmeric paper. The original water does not immediately and sensibly affect the test paper, but if it be heated, in the air at least, it gradually affects the paper when left in it. All the effects show that the silica for the time neutralizes in part the alkali, and that the latter shows its power as the former is by the evaporation gradually separated from it.

The deposits are all essentially siliceous: most of them have the silica in combination with water as a hydrate, and it is probable that a little alkali is contained in them. The red portions are produced by oxide of iron, derived, I believe, not from oxide of iron contained originally in the waters of the Geyser, but from the action of the alkali precipitating some chalybeated portions of water which it meets with in its course. I think you said that the red deposit does not occur at the spring, but at the place where the waters run into the river.

The waters contain, besides silica, &c., sulphate and muriate, probably of the alkali soda, for there is no sensible portion of lime present; but these, or at least the muriate or the chlorine is probably in a peculiar state of combination, for when nitrate of silver is added to the original water, i.e. before the silica is separated from it, it causes but a very slight precipitate; and yet the addition of a little nitric or sulphuric, or even acetic acid, produces an abundant precipitate of chloride of silver. This is an effect which we should not expect, and shows the interference of something for a time, which interference is removed by the presence of the acids. The quantity of water was so small, that I was not able to satisfy myself of the exact nature of this action.

The specific gravity of the water is 1000.8.

I presume that the deposition which takes place from the waters at the spring is quite of the same nature as that which occurs on the evaporation of the portion you brought away; the water coming from the earth in its fresh and hot state fully saturated with silica, and holding more of it than it can retain when it cools and is exposed to the air. I should not think it would be an impossible thing by art to imitate the whole effect².

With regard to the surturbrand, I have nothing to say about it which is not well known, and I believed published. The specimens of the deposits I shall have the pleasure of laying before the next Board of Managers³, and in the mean time beg to return you our thanks for them.

M. Faraday

John Barrow, Jun., Esq.