Faraday to John Gage   2 June 1835

<q>Royal Institution, June 2, 1365.

My Dear Sir,

In the midst of the pressure of much occupation which will admit of no delay, I commence account of the matters you gave me in charge for examination, and hope I shall be able to finish it in time to suit your convenience.

It is nearly three weeks since I took the portions I possess from the various articles in your custody, and, if my impression is correct, you wished me to notice any thing which at that time caught the attention. I shall do so therefore in some degree, though at the risk of noticing some points which you will have touched far more minutely and accurately than I can do.

The article which we called a camp-stool has been constructed principally of iron, and much of that metal still remains in its original state under the coat of oxide.

The upper horizontal bars were tipped with knobs of bronze; which have resisted decay in a manner very far surpassing the iron. The white incrustation upon them, which I at first considered as being probably oxide of tin, is only carbonate of lime, and has been derived from the calcareous matter with which the stool has been in contact.

You will recollect that at the corners of the upper horizontal bars were appearances as of the remains of the straps or bands which had formed the seat of the stool when opened. These appearances did not consist of any difference in the colour or even nature of the substance there from that on other parts of the bars, the whole was rust or oxide of iron: but at those corners might be distinctly observed the form as of the ends of bands. These bands appeared to have been either leather or hide; for there was still the character of the surface of the skin, the sharp cut edge, the little curl up at the edge, the small wrinkles where the tension of a tight pull round the corner had not been uniform; there was also the long notch or slit through which the descending bar of the stool has passed: and the junction or union of the substance beyond that part: all these were indications of the former existence of a strap there, and seemed to imply that it was either of skin or leather. I have already said that the substance here resembled in appearance that of other parts; but when it was heated it gave much more ammonia than they did; and when projected on to fuzed chlorate of potassa, there was scintillation, as if a little organic matter still remained.

The next article I will notice, is the beautiful enamelled bronze vessel with the loose handle. This, since it has been cleaned, will reveal its own nature to you. It appears to me that the cavities in which the enamels are placed have certainly been finished with the chisel, before the enamel was introduced, otherwise the angles could not have been so sharp as they are. Whether they have been altogether formed by that tool, or partly produced in the casting, I cannot say. The enamels are true glasses; not encaustic, as commonly understood; and the solid portions selected, were found but very little changed in their nature. The colours are three, blue, red, green, and without any shades of difference. The blue is a deep translucent colour, and is due to cobalt. The red is an opaque colour produced by copper. The green is, I think, copper; but that is more difficult to determine from the smallness of the portions taken, and the constant presence of that metal derived from the bronze. The part of the bronze left uncovered by the enamel appeared to have been gilt all over; but upon close examination I could find no gold; the appearance was that of the bronze only.

The Lamp. - After removing the loose dirt and other matters which had fallen into this vessel, there was found in the body of it a cracked cake of a sub‑stance, dry, brittle, earthy in appearance, about half an inch in thickness, and rather light. It was of a greyish colour, but the upper surface black, and the lower green from the contact of the bronze. This substance was altogether combustible; but it could be separated into two portions, one a fusible fatty body, the other not fusible, and dark in colour. The whole consisted of a fatty fuel much changed by time, or perhaps, in part, by the heat which had resulted from the combustion of the lamp in former ages. I am inclined at least to think the blackness and infusibility of part of the substance, is due to such an action; for in lamps of this construction, where the wick is in such near vicinity to the general mass of oil, much of the oil that has been highly heated in the wick returns into the body of the fuel. It is remarkable that this fuel has not assumed that condition in which it would have constituted a fatty acid: it is not like the fat in soap, capable of free combination with an alkali, nor abundantly soluble in alcohol.

The wick of the lamp was in the state of half burnt fibrous matter, and about an inch in diameter. It is in its nature vegetable, but I cannot say what particular substance it is.

The bronze leaf which rises from the handle must have struck you as being not merely very ornamental but also as a shade to the eyes, a protection to the hand when the lamp was carried, and a counterpoise by its weight to the projection of the lamp at the place of the wick: the lamp would in fact be very unsteady without it.

And now with regard to the narrow long-necked glass bottle. This bottle would hold probably about half a pint. It was full to the top; the contents being partly aqueous, and partly solid and liquid fatty matter. The bulk of the contents had not sensibly diminished; for a portion of asphaltum, or some substance resembling it, had been used to close the filled vessel; this had taken an impression from an irregularity in the form of the inside of the neck close to the top, and this irregularity, and the corresponding indentation in the asphaltum, were still nearly in contact; the part below being quite full of solid and liquid matter. This solid substance, which I have called asphaltum, was black, hard, heavier than water, and burnt with flame having the same appearance and smell as asphaltum. There was but a small quantity of it, perhaps a quarter of an inch in depth.

Below this black cement was a dry solid substance, and then a mixture of solid and liquid, all being fatty and of the same general nature. A very little heat dissolved the solid matter in the liquid, and an oil resulted. This oil was lighter than water, of a yellow colour, burning with a bright flame, producing a red colour on litmus paper; dissolving abundantly in alcohol, and combining with alkalies so readily as to produce much heat. It was in fact fatty acid, and in that respect unlike the fat in the lamp, but like that which was found in the square narrow-mouthed bottle of the tumulus formerly opened in the same place¹; except that that was solid fat, and this partly solid, partly liquid. Whether this fatty acid is the result of the spontaneous change of oily matter at first in its natural state, which has remained so long nearly or entirely excluded from the air; or whether it had been made hot or otherwise treated before being introduced, and so a change induced upon it at that period, I cannot say; but my impression is, that the change has been the work of time.

At the bottom of the bottle, beneath and amongst the fat, was an aqueous liquid sufficient in quantity to occupy about one third of the contents of the whole bottle. It had a pale brown colour; was very sweet to the taste (with a degree of roughness on the tongue); and had a faint vinous or apple-like smell. By exposure to air it, in a few days, became darker in colour, and lost its smell. It was slightly acid; was darkened in colour a little by per-sulphate of iron, as if a trace of astringent matter were present. It was heavy, descending rapidly through water, and forming strong striae during its solution in it. It mingled freely with alcohol, no turbidness being produced. Being evaporated it left a large proportion of a sweet thick syrup, which by more heat burnt like sugar or honey, leaving an alkaline trace behind. I could not discover any indications of an animal origin for this substance. I do not think it had been mere wine, it was too dense a solution for that; my impression is that it has been honey mingled either with water, wine, or some aqueous fluid at the time of its introduction; for the superposition of the oil in the vessel, and the gene‑ral appearances, forbid the supposition of the water having been obtained by gradual abstraction from the atmosphere.

The next vessel that I will refer to is the bottle with two handles. Its ca‑pacity is about a pint and a half; and, though open, it was nearly four-fifths full of an aqueous fluid, at the bottom of which was a thick mass of mucous matter resembling in its appearance the similar substance frequently produced during the decay of vinegar and other vegetable solutions. The contents of this vessel had a faint smell resembling rhubarb; the liquor was of a pale yellow colour, clear, not sensibly acid or alkaline, and nearly tasteless, having only a slight mouldy flavour. The colour scarcely changed by the addition of acid or alkali. Traces of a sulphate and muriate could be found in the fluid by the proper tests, but scarcely any lime or earthy base.

When the liquor was evaporated considerably, it left a small quantity of coloured residue which was slightly alkaline before burning; when heated it blackened, yielding only slight traces of ammonia, and the ash that was left was very alkaline, the alkali being potash. I then examined the coagulum that was at the bottom of the liquid. When pressed between litmus paper it was very much diminished in size, indeed scarcely any thing solid was left. The remaining substance burnt precisely like vegetable matter. My impression is, that the liquid in this bottle is the result of the decay of some vegetable solution, but whether wine, vinegar, or any other particular liquid, I cannot guess by any indications derivable from its present state.

There was also amongst the articles I saw and examined, a long-necked small glass vessel which was dry inside, and contained only a few loose fibres of dry solid matter. Parts were brown and parts black in colour, and these differed from each other in their qualities, being distinct substances. The black portion burnt with a feeble flame and perhaps contained a little asphaltum. The other burnt, but scarcely with flame. I can, however, say very little about them².

The presence of the aqueous fluid in the double-handled open bottle, leads me to hope that you will particularly consider the state of the cavity from whence these vessels were taken, as to its degree of dryness or dampness. Do you recollect whether the level of the cavity is above or below the level of the surrounding land? and was any notice taken of the state of the air in the cavity when first opened?

I am, my dear Sir, | very truly yours, | (signed) M. Faraday.

John Gage, Esq. F.R.S.