London Institution,
January 16th, 1838.
Dear Sir,
One of my duties in connexion with the Philosophical Magazine is the editorial sending of the proofs. In this way your paper <1> on a new property of Nitre has come before me; and as I think that some of your remarks in the first page will excite ca<s?>illing criticism which if inserted as they now stand, I have restrained the printing of the sheet until I should have an opportunity of communicating with you and learning your decision on the points in question. May I request therefore you attentionr to the following observations:
Your remarks on the formation of crystals by successive depositions on a nucleus appear to me to apply only to the production of crystals in aqueous solutions, and not to their production by the cooling of bodies previously Signified by the mere action of heat – by igneous fusion. In many cases of the latter kind, if not in all, the formation of crystals obviously takes place as you have stated in p 147, the crystellization of fused nitre to proceed Further, you state, p 145, your belief that it is the received opinion that the structure not only of quartz but of all crystals is so destroyed by fusion as not to be recovered, in growing cold. Now this, I think, can hardly be the “received opinion”; as it is known that so many crystalline bodies, not merely in nature, but also in the operations of the arts, are produced by solidification from a state of igneous fusion. It is scarcely necessary to cite, as examples, merely all the crystalline minerals constituting what are called per excellentian “the crystalline rocks;” and the artificial felspar, pyroxene, mica, & epidote of Mitscherlich <2> & Haussman. We know, further, by experiment, that if a rock consisting of crystalline felspar & pyroxeve be fused, & then slowly cooked, those minerals and consequently the rock itself are reproduced; but if rapidly cooled, it becomes a glass. I strongly suspect that the case of the fused quartz is parallel to this. In so far as the notion you mention may be or may have been the received opinion, its origin, I think, must be sought in the confusion which has existed and still exists to a considerable extent on the subject of “water of crystallization”; and the nature of the crystalline bodies containing it. It was thought, not long since, that certain salts would not crystallize but in confirmation with this water, and that when it was expelled by the agency of heat they lost their power of crystallization unless again combined with water by solution. It is perfectly true that the crystalline structure of such salts is so destroyed by fusion as not to be recovered in growing cold, if the water be expelled. But if they be cautiously fused – in their water of crystallization undergoing what has been termed the “watery fusion”, upon cooling they recover all their former properties. It was moreover quite overlooked that these are properly fused hydrates of the salts: if the heat be further merged, after the expulsion of their water, so as to fuse them, they will then crystallize on cooling, though in very different forms from those which they assume in crystallizing from aqueous solution, – being, in fact, different chemical compounds. But those salts which crystallize from water without retaining it as an element, of which Nitre is one, have the same primary form whether they crystallize from aqueous solution or igneous fusion.
I inclose a proof of your paper, and should you think proper, after considering the remarks I have offered, to modify your own, have the goodness to alter the proof accordingly and return it as speedily as may be convenient. I have already been prevented from addressing you on the subject so soon as I intended.
It would be very interesting to ascertain what are the optical properties of nitre while in the fused condition. As Biot <3> has shown that many crystalline bodies exert their characteristic action upon light when in a state of solution, we may reasonably expect to find that such also is the case with others the liquifaction of which is effected by simple fusion.
I had the honour of receiving from you many months since a request to make my acquaintance and I called in Sackville Street <4> in consequence, but you were in Devonshire. I need scarcely say that I shall be most happy to become further acquainted with you. It is now nearly ten years since Mr. Faraday <5> intended to have introduced me to you, from my then wishing to suggest some experimental inquiries on refractive power. These, which I still think important, have never yet been made, but I am turning my attention to the mineralogical part of the subject, and if agreeable, will offer you my suggestions on that which is properly optical.
I have the honour to subscribe myself
Dear Sir,
With much respect, Very truly Yours,
E. W. Brayley
H. F. Talbot Esq.
&c &c &c
Notes:
1. WHFT, ‘On a new Property of Nitre’, Philosophical Magazine, s.3 v.12 n.73, February 1838, pp. 145–148.
2. Eilhard Mitscherlich (1794–1863), German mineralogist & chemist.
3. Jean-Baptiste Biot (1774–1862), French scientist.
4. 31 Sackville Street, London residence of the Feildings, often used as a London base by WHFT.
5. Prof Michael Faraday (1791–1867), scientist.