Faraday to William Savage   8 October 1818¹

Royal Institution | Oct. 8, 1818.

Dear Sir,

I have, in obedience to your desire, analysed the Specimens of Paper which you sent me; and herewith send you an account of their chemical nature². I will describe the result of the analyses, without any reference to their applicability, and afterwards make such observations as may suggest themselves.

One thousand grains of French Plate Paper, dried at 212°, were boiled for some hours in repeated portions of distilled water, until every thing soluble was separated from it; the solutions were filtered and evaporated; and, when reduced to a pint, formed a clear transparent fluid, of a pale yellow colour, which precipitated with galls, and very slightly with alcohol: when evaporated considerably, it gelatinized on cooling; and, on being dried, at 230° weighed 15.2 grains. Afterwards, treated with alcohol, 2.5 grains of extract were dissolved out; and the rest, with the exception of .7 of a grain of sulphate of lime, appeared to be gelatine.

Five hundred grains of the same Paper was burnt, piece by piece, in a pair of forceps, and the ashes received in a basin. They were not alkaline, nor did they effervesce on the addition of muriatic acid. Heated, until the excess of acid was driven off, the soluble salts were washed out with distilled water and filtered, and gave, alumina 2.4 grains; lime 0.6 of a grain; oxid[e] of iron 0.7 of a grain.

The insoluble ashes were heated in a crucible of platinum with a little nitrate of ammoniac, to burn off the adhering charcoal, and left 2 grains: this analysed gave 1.3 grain of silex, and the remainder sulphate of lime.

One thousand grains of dried Yellow India Paper, treated in the same manner, gave, first, a clear solution of a light brown colour, which precipitated with galls, and lightly with alcohol. It contained a very little muriate of lime and muriate of soda. Dried, it became a dark brown solid substance, weighing 19.5 grains. Alcohol dissolved but a very small portion of it; and it was not very soluble in water: hot water dissolved it more readily than cold water; and when a hot saturated solution of it was cooled the substance precipitated, and the solution became opaque. Galls precipitated it readily, and there was apparently, from the nature of the precipitate, some gelatine in the solution; but by far the greater part of the substance appeared to me to be a peculiar extractive matter.

Five hundred grains burnt, gave ashes very strongly alkaline, and effervesced abundantly when acted upon by muriatic acid. The soluble salts, separated and dried, weighed 5 grains; and (the lime being converted into a carbonate, the state in which it existed in the paper) 3 grains of carbonate of lime, 1 grain of alumina, and 0.5 oxide of iron.

The substance unacted upon by acid, gave 4.7 grains of silex, and 0.6 of iron, with a little alumine.

One thousand grains of White India Paper gave a light yellow coloured solution; precipitated lightly by galls, alcohol, nitrate of silver, and oxulate of lime. Evaporated to dryness, it split in various directions across the capsule; and weighed 21 grains. Like the substance obtained from the yellow paper, it was scarcely touched in some hours by alcohol: it was not very soluble in water; but more so in hot than in cold water: and, with the exception of a little muriate of lime and muriate of soda, I concluded it to be a peculiar extract.

The ashes (of 500 grains) were strongly alkaline, and effervesced with muriatic acid briskly. The bases of the soluble salts formed, separated from each other, were as follows; 9 grains carbonate of lime; 4 grains alumine; 0.8 of a grain oxide of iron; and a small quantity of soda. The insoluble residuum examined, gave 1.3 grains silex, and 0.4 of a grain of sulphate of lime.

I was somewhat surprized to find so great a difference in the quantity of earthy matter afforded by the two kinds of India paper; and still more so by the excess being on the side of the white paper. I had expected the contrary effect in a slight degree, from the supposition, that the material of the white paper had been submitted to cleansing processes; and I was justified by the results in a similar judgement respecting the French plate paper. That, however, I am nearly correct in the quantities I have given, though they oppose the preconceived opinion, is shewn by their near accordance with the weights of a more general analysis that I gave you some time since.

During boiling, the yellow India paper broke down into a magma, and formed a sort of paste. The white paper did not suffer so much in this way; and the French plate paper scarcely any thing.

I have been thus precise in describing the analyses, and the results afforded by them, rather to satisfy your earnestness, than from an opinion that they present any thing capable of improving the art of paper making: and I should expect that matter much more interesting would arise from an examination of the mechanical properties of the paper, and more applicable to the improvement of our own manufactory.

I have no doubt myself, that the superiority of the India paper is owing to the peculiar nature of the fibre used in its formation, and not to any particular process in the manufacture of it, or to the addition of any other substance. Indeed, as far as regards the making of it, I think it inferior to our own; but it has a singular degree of ductility, even in the dry state, which far surpasses any thing I have observed in European paper: the slightest impression of the nail, or other hard body; the mark of a twist, or any form given to it by pressure, remain very perfectly after the force which produced them is removed; and by simple extension of the paper, or other means, these may be removed much more readily and completely than they can from a piece of English paper. Now, I presume that it is to this property, and which belongs to the peculiar fibre of which the paper is composed, that it owes its superiority: it permits the paper to mould itself according to all the inequalities of the surface against which it is pressed; and, consequently, entering and filling up more accurately the lines upon the copperplate, it receives the ink from every place where it has been deposited, in a more perfect manner than any paper deficient in this quality can do. I endeavoured to convince myself of this, by scratching and cutting up a copper plate with a steel point, and then covering one half with folded India paper, and the other with French plate paper, submitting the surface thus covered to pressure: I found, on removing it, that though both papers had been in precisely the same circumstance, there was an essential difference in the impressed form received by them; on the French plate paper I could only trace the elevations formed by the deeper lines on the copper plate; but on the India paper every mark could be observed which the copper that it covered had received.

I will not extend these observations further than to express my opinion that the two sorts of India paper are made from the same substance; and that previous to its having passed through any other manufactory. It is probable that the large quantity of carbonate of lime in the white paper results from the use of lime in some state in the process of whitening; and the deficiency of silex in it would be a necessary consequence of its having undergone a more extensive series of processes.

I do not think that any thing has been added to the pulp of the India paper to make the fibres adhere, except perhaps to the yellow paper, where a little gelatine appears present; and where, from greater tenuity in the paper, it might be necessary. It is possible, however, that the whole of the extractive matter has been added; but I am inclined to believe it comes from the fibre. Your researches, however, may probably have enabled you to make a much better judgement on this and other points than I can do; and I will therefore cease troubling you with further conjectures.

I am, Dear Sir | Very sincerely yours, | M. Farraday

Mr. W. Savage