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Letter from DR. MAC CULLOCH to the Editor, respecting some Miscellaneous Inquiries.

In turning over my note-book, I perceive, among a variety of miscellaneous matter, of which many are subjects for distinct papers, some facts and remarks which I am tempted to transcribe for you in a letter, as being too short for any other purpose; while I am unwilling that they should perish, as so much of what is entered under this form does every day. In this instance, where they refer to statements in your own Journal, I am sorry to say that I can neither point out the writer nor the number; having neglected to enter either when the remarks on the particular passages were made.

It is observed somewhere there, that no analysis of the produce of gunpowder, after combustion, has been given by chemists, and that the generated gases remain unknown. If the author who has committed this oversight will take the trouble to refer to the Supplement of the Encyclopædia Britannica, he will find the analysis in question, both as it concerns the gaseous and the solid produce. I need not, therefore, transcribe it here, to occupy your pages for no purpose. At the same time, I would gladly see that analysis repeated now, by abler hands, and by the more accurate means of analysing mixed gases which the chemistry of the present day furnishes. It is thirty years since it was performed, and with no very refined apparatus; so that it is probable that the relative proportions are not as accurate as they might be rendered. I will not even say, now, that it is entirely correct in the mere substances; but they who laboured at that distant date, and undertook such an analysis also, as one of their first problems, will not be very severe on the errors that they may discover.

In one of your recent numbers there is also recorded the Discovery, by an Italian Chemist, of a concrete adipose substance to be obtained from Essential Oils. That discovery was published by myself, nearly twenty years ago, in Tilloch's Journal, though I have not the series at hand, so as to point

out the year or number. Of many experiments which I afterwards made on it, there are none in addition to those published (if I now recollect right, in two papers) that are of much importance; but some further remarks made on some of the oils may be worth mentioning, as they lead to an important conclusion as to the essential oils in general.

In this paper, I observed that the formation of this substance, which bears a nearer resemblance to spermaceti than adipocire, depended on age; since it is never found in new oils. That it is the consequence of the action of oxygen, is probable, if not accurately proved; and it increases with the age of the oil. In some specimens of the ottar of rose, which I know to be at least thirty years old, the whole has become a nearly solid mass, from the formation of this substance. By extracting from it, with cold alcohol, such of the liquid oil as remained, it did not even divide into parts, but remained a somewhat porous yet continuous substance. But as to this particular essential oil, there is an observation of some practical value that deserves record. The spermaceti (since I do not choose to coin a name) is inodorous; and it appears that during this change the odoriferous principle, be that what it may, is destroyed. This is proved by these specimens ; for I did not procure from a drachm of this ancient oil more of the odoriferous, alcoholic solution, called essence of rose, than a few grains of the fresh and liquid oil would have yielded. And I can conceive that in perhaps as many more years, or less, the whole of the odours would have disappeared. This fact may prove of use to possessors as well as to purchasers; since the former ought not to keep this oil long, as is commonly done, nor the latter to purchase, if they have a choice, that which is concreted.

Of all the oils that I have examined, that of aniseed appears to yield it in even greater quantity than the ottar of rose. A specimen now in my possession, after about twenty-five years, is a solid, and as white as tallow; scarcely containing any liquid oil, while the quantity of odour or odorous matter is also reduced to almost nothing. I cannot discover that there is any sensible difference in this spermaceti from whatever oil it is procured. In the oil of lavender, it appears to require much

longer time to be formed in any quantity.In that of berga mot, it is much more abundant in the same time; but it is still in very small proportion compared to that in the oils of anise or the rose.

But, that I may not prolong this paper by noting the oils in which it does occur, I may proceed to say that there are many in which it never is found. Such, among many more, are those of juniper, the fir tribe, or oil of turpentine, and that of cloves. And these oils undergo a very different change from exposure to oxygen. They become first thickened, and finally are changed into resins; while in the oil of the fir-tribe this change is even rapid, as is familiar.

And the general conclusion is interesting to chemistry; since it shews that there are two distinct kinds of essential oil, bearing the same analogy to each other that the fat and 'the drying liquid oils do in another division of these inflammable substances. Oxygen converts the one set into spermaceti, and the other into resin; just as, in the latter, it renders the one rancid, sometimes also tallowy, while it converts the other into an elastic varnish, a solid. And hence another division of these substances is required. We must make two species or genera of the oils that are evaporated, or perhaps some times formed, at or below the boiling point of water; as we have made two of those that do not evaporate under between 500° or 600°,' and are obtained by expression, if from vege tables. And it is not unworthy of remark that, in the animal kingdom, we find two oils of this latter nature, which nearly represent the two species or genera of the essential oils. The oil of the spermaceti whale is converted, partially, if not entirely, into spermaceti, by exposure to oxygen, whence also it loses its property of burning readily by age; while that of the Greenland whale is, by the same action, converted into varnish, or becomes a drying oil.

But as it is not my object here to write another essay on this subject, I shall terminate: nor should I have noticed the discovery of this Italian Chemist, for the vulgar purpose of claiming it as my own, had he not overlooked the most im portant conclusions, and indeed had he not left the subject little else than a mere record of a fact, without bearings or

interesto If my own papers were so far forgotten as they appear to have been, some time might yet have passed before his discoveries would have been brought to the present conclusions, since they would have formed the point of departure for himself or other experimenters; and there is so much to do in chemistry, that it is ill policy to waste time in discovering what has been discovered before.

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On the subject of iodine, every new fact, however insulated, is interesting. Of all the marine plants which I have examined, it is contained in the largest quantity in one which was formerly called Fucus pygmæus, which is now, perhaps, better known to most botanists by its ancient name than by the modern one, which has transferred it to the lichens. And it is best to give it the name that is best known; as the present is not a question of botanical criticism. The very smell of this fucus is almost suffocating; resembling that of iodine when confined in a bottle: but as it is not a bulky plant, though an abundant, one where it grows, it never can be a convenient one from which to procure this substance.

I have examined the lichens to some extent, though much less than I desired, in hopes of finding iodine in them, and I wish to point out this investigation to those who have the opportunities which I have now long lost. I have reason to believe that it will be found somewhat widely; but in particular I wish to direct the attention of chemists to the lichen cæsius; a liche even under the present nomenclature, unless it has again, been changed, under that system which has determined that our memories shall not rust for want of exertion. It is sufficiently common on stones, and ought to be well known to every botanist. God to deILY

noLastly, having been interrupted in some experiments which I may never be able to renew, I wish that some chemist would examine into the nature of the lilac dye produced from certain, lichens, especially from the roccella; since it is not impossible, that this colour may be derived in some manner from the e substance in questions to bio i 8 at 925 bi

To have mentioned dyeing, reminds me of two lilac dyes which I have produced, amongst some other things, which I must defer to a future opportunity, from plants of domestic growth, not hitherto applied to this purpose. The one of these is the berry of the Portugal laurel, and the other the black currant. The simplest process with alum, which I need not describe, is all that is required for either; but, as far as my trials go, the best tint is produced by the former fruit. It is as pure and brilliant a lilac as that from the lichen roccella; but it is far more valuable, inasmuch as it is not reddened by acids, the great evil of all the lichen dyes, nor, as far as I was able to ascertain, by perhaps insufficient trials, so easily injured by the sun. And the preparation of the dye itself is comparatively nothing; so that, as far as this is concerned, the expense would be far less. The question, however, remains-what would be the expense of cultivating this tree for its fruit, compared to that of importing the lichen roccella. This I have no means of ascertaining at present: but it could not be a very difficult question to a nursery gardener; while also, were there a demand, the berries, perhaps, might be furnished cheaper from its native climate. Mr. Macintosh, whose name is authority on such a subject as this, seemed to think, on a general view, that it might be profitable: but I need say no more, where I meant only to offer a suggestion to those who may feel an interest in inquiring further into this subject.

As to the black currant, the produce on any given piece of land is considerable; and there are collateral purposes in this fruit which might render it easier to cultivate it to a profit for the sake of the skins in dyeing. The fruit might first yield marketable jelly, by the usual process, or might even be made into some sort of wine; while the marc, in either case, would be the dyer's material.

Let me conclude these miscellaneous notices by pointing out an unobserved formation of a neutral salt, which I find it very difficult to explain. It is the nitrate of ammonia. In the house which I inhabit in London, on returning in Decem