[draft:] ^<1>

To Brewster
March 22. 1833

Remarks On [illegible deletion] Ch. Ch^ges of Col^r

So little is kn conc^gye Cause of the var ch^gesof C w^ch arise in Ch^l exp^tsthat any contrⁿtow^ds may hope to be fav^ly rec^d

Very little is knⁿ with certainty conc^g ye Causes or causes of ye of those strik^g Ch^ges of C which we so freq witness in Ch^e exp^ts. No theory has yet been proposed w^ch will ^is by any means acc^t for the whole of ye phæenom^a of them & we are often at a loss even for a plausible explan^n. And yet these phæn^a have probab^ly a some very intimate connexion with the ultimate constitution of bodies, & are therefore well worthy of our marked partic^r attention. I will therefore mention a few facts relating to this subject hoping to engage others to pursue the subject such enquiries further.

Water being a colourless subs^tce ought, one would imagine, when mixed w^th other sub^stces possessing no decided colour, to produce a colourless compound. Neverthe^less it is to water only that the common Vitriol or Sulphate of Copper owes its extremely vivid blueness: as is plainly evinced by a simple exp^t. For if we calcine & pulverise the vitriol at a low red heat, & pulverise it & reduce it to powder, we shall obtain a powder of a dull & dirty white appearance. Now Pour a little water upon this and a slight hissing noise is heard, accompanied by an evolution of heat, very similar to what happens in the slaking of quicklime. At the same moment the blue colour suddenly reappears. M^r Faraday to whom I exhibited showed this exp^t. informed me it was new to him, I therefore presume that it is a fact little if at all known, & may interest your chemical readers.

Under the microscope this is a very pretty exp^t for the instant a drop of water is placed in contact w^h the vitriol, the amorphous powder is seen to shoot into blue prisms. Are we then to infer that water has a tendency to communicate a blue rather than any other colour, to bodies in general? By no means, for in other instances its operatⁿ is exactly the reverse, and it is a destroyer instead of a promoter of blueness.

For instance: Sulpt. of Molybd. is a liquid of a very rich dark blue, when suffic^ly concentr^d but a very small portion of water suffices entirely to destroy annihilate this blue tint, and to leave the produce a mixture which is perfect^ly limpid colourless. Thus the action of water upon the two metals copper & molybdenum is of an entirely opposite character: Instead of water, if Ammonia be used, the same contrast appears, but is seen still more strikingly as

* Muriate of Copper is described in most books of Chem^try as a liquid of a bright green colour. But how imperfect an account of [illegible deletion] it this is, will be seen from the foll^g exp^t – If sulph. Copper & mur. lime (dry, or only slightly damp,) be pulverised together in a mortar, mur. of copper is formed of a dark yellow colour* illegible deletion. If a few drops of water are now added, the yellow speedily changes to a bright green. If more water is added, the liquid mixture becomes greenish blue, sky blue, & finally colourless. If the water is evaporated by heat, the same colours reappear in the reverse order.

In Turner’s elements of Ch^ry it is said that Nitric acid [illegible deletion] when combined with containing a small portion of the yellow orange Nitrous gas, assumes a green tint & this remark upon which the author takes occasion to make the follow^g remark

Now the a

Now the above ment^d prop^y of Mur. Copper seems to furnish an [illegible deletion] instance that is very analogous to this.

*another striking remarkable but and well known instance analogous to this is the Mur Cobalt, which is entirely deprived of its fine blue colour by a very slight admixture of water.

The mere application of heat often produces great change of colour, which disappears when the subs^tce again becomes cold. The red oxide of lead Red lead, vermilion & white oxide of zinc are instances well known, & never accounted for – Another curious example is furnished by the Sulph. Molybd. which when warmed loses changes its fine blue tint, to a pale yellow, again when cold reverting to the blue.

* Correction. Here insert “or more frequently yellowish brown”

[expanded version:]

To Sir David Brewster

March 22, 1833

Remarks on [illegible deletion] Chemical Changes of Colour

So little is known concerning the cause of the various changes which arise in Chemical experiments that any contribution towards may hope to be favorably received Very little is known with certainty concerning the cause various causes of the of those striking changes of Colour which we so frequently witness in Chemical experiments. No theory has yet been proposed which will by any means account for the whole of the phænomena of them and we are often at a loss even for a plausible explanation. And yet these phænomena have probably some very intimate connexion with the ultimate constitution of bodies, and are therefore well worthy of our marked particular attention. I will therefore mention a few facts relating to this subject hoping to engage others to pursue the subject such enquiries further.

Water being a colourless substance ought, one would imagine, when mixed with other substances possessing no decided colour, to produce a colourless compound. Nevertheless it is to water only that the common Vitriol or Sulphate of Copper owes its extremely vivid blueness: as is plainly evinced by a simple experiment. For if we calcine and pulverise the vitriol at a low red heat, and reduce it to powder, and pulverise it we shall obtain a powder of a dull and dirty white appearance. Now pour a little water upon this and a slight hissing noise is heard, accompanied by an evolution of heat, very similar to what happens in the slaking of quicklime. At the same moment the blue colour suddenly reappears. Mr Faraday ^<2> to whom I exhibited showed this experiment informed me it was new to him. I therefore presume that it is a fact little if at all known, and may interest your chemical readers. ^<3>

Under the microscope this is a very pretty experiment for the instant a drop of water is placed in contact with the vitriol, the amorphous powder is seen to shoot into blue prisms. Are we then to infer that water has a tendency to communicate a blue rather than any other colour, to bodies in general? By no means, for in other instances its operation is exactly the reverse, and it is a destroyer instead of a promoter of blueness.

For instance: Sulphate of Molybdenum is a liquid of a very rich dark blue, when sufficiently concentrated but a very small portion of water suffices entirely to destroy annihilate this blue tint, and to leave the produce a mixture which is perfectly limpid colourless. Thus the action of water upon the two metals copper and molybdenum is of the entirely opposite character: Instead of water, if Ammonia be used, the same contrast appears, but is seen still more strikingly. as Another striking remarkable but and well known instance analogous to this is the Muriate of Cobalt, which is entirely deprived of its fine blue colour by a very slight admixture of water.

Muriate of Copper is described in most books of Chemistry as a liquid of a bright green colour. But how imperfect an account of this it this is, will be seen from the following experiment– If sulphate of copper and muriate of lime (dry, or only slightly damp) be pulverised together in a mortar, muriate of copper is formed of a dark yellow colour or more frequently yellowish brown [illegible deletion]. If a few drops of water are now added, the yellow speedily changes to a bright green. If more water is added, the liquid mixture becomes greenish blue, sky blue, and finally colourless. If the water is evaporated by heat, the same colours reappear in the reverse order.

In Turner’s Elements of Chemistry it is said that Nitric acid [illegible deletion] when combined with containing a small portion of the yellow orange Nitrous gas, assumes a green tint and this remark upon which the author takes occasion to make the following remark ^<4>

Now the a

Now the above mentioned property of Muriate of Copper seems to furnish an [illegible deletion] instance that is very analogous to this.

The mere application of heat often produces great change of colour, which disappears when the substance again becomes cold. The red oxide of lead Red lead, vermilion and white oxide of zinc are instances well known, and never accounted for – Another curious example is furnished by the Sulphate of Molybdenum. which when warmed loses changes its fine blue tint, to a pale

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Notes:

1. Draft of WHFT’s paper ‘Remarks on Chemical Changes of Colour’, Philosophical Magazine, s. 3 v. 2 no. 11, May 1833, pp. 359–360.

2. Prof Michael Faraday (1791–1867), scientist.

3. Brewster had become an editor of the Philosophical Magazine.

4. “It is difficult to perceive how an orange-coloured liquid should give different shades of green and blue merely by being diluted“. Edward Turner, Elements of Chemistry: Including the Recent Discoveries and Doctrines of the Sciences, 4^th edition, enlarged and carefully revised (London: John Taylor, 1833), p. 193.