Imatges de pàgina
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ber, after an absence commencing with March, during which, I presume, the windows had not been cleaned, the whole surface of the glass was found covered with drops resembling oil. Attracted by this appearance, I examined them, and found that they had a saline taste; and when the room became heated by lighting fires, they crystallized; continuing to alternate between deliquescence and crystallization, according to the state of the atmosphere, until I had collected them for examination.

I do not know of any formation of nitrate of ammonia from the atmosphere, though it probably takes place in nitre beds. and dunghills. Yet here, there is a reason for the ammonia; as that for the nitrous acid is familiar. But the alkali, be it what it may, is, in these cases, with formation of nitre, existing in the soil, or at least supposed to be there, while it could not have existed on the glass. Nor was there aught in the room, or in the house, an excellent, large, and especially clean and pure house, without smells or drains, or anything else of this nature, to generate ammonia. If it be so, the ammonia also, as well as the nitrous acid, is formed from the atmosphere; and it is probable that not only this, but potash itself, is thus produced; since in no other way do we know how to account for the formation of nitrate of potash, at least in open soils, where no free potash was ever yet detected. Such is the fact which I had to record. It might be of comparatively small moment by itself; but if it shall ever aid to throw a light on the mysterious formation of nitre, it will not be without its

use.

Believe me your very

obedient servant,
J. MAC CULLOCH.

We have frequently remarked small radiant and arborescent crystallizations on dirty windows in London, and have found them to consist of sulphate of ammonia. This salt, or at least sulphite of ammonia (which becomes sulphate by exposure to air), is an abundant product of the combustion of coal, and to that source its presence in the above instances is probably to be referred. The ammonia alluded to by Dr. Mac Culloch is, doubtless, of similar origin.-Note by the Editor.

.de bæof bitrode soi sawa þy to an obizza bonidmo Observations on the manner of Manufacturing Indigo † in the 1 Southern Provinces of India; with some Remarks on its Chemical Changes and Combinations. By Charles Hi Weston, Esq.

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DR. BANCROFT introduces his observations on Indigo by the following strong expressions: "The subject of this article is the most interesting, important, and instructive, which can occupy the attention of a dyer or a chemist; the admirable and singular properties of indigo being only surpassed by those of the colouring matter of the murex and the buccinum a little, while it is of much higher practical utility than the latter." Perthan the a per haps there are few men better qualified to form an estimate this point than Dr. Bancroft, who had removed from the art of dyeing generally so much that obscured it, and had thrown so much light on the changes and chemical characters of indigo in particular.

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Not only, however, has it claims, from its peculiar chemical characters, upon the attention of the scientific man, but the 71190 Important part it now holds in our exports from India must also interest the man of business in its favour. The indigo the East Indies, which at one time ranked so, low in its bid portsm comparative value, has, by a better mode of manufactu fmanufacture, been progressively improving, and, consequently, as gradually ing its way into European markets, till, at length, the making its way exports of the West, of Spanish America, and the West Indies, have been to a great extent transferred to the East.† This is a conquest indeed, but it is a conquest which English 10.r intelligence, as well as enterprise, has accomplished. To those, therefore, in whose minds the bare mention of the word "theory" is "but too apt to call into action every latent prejudice, and to secure to it the most determined opposition, this very striking instance before us, among many others which are daily occurring, of the great advantages resulting from the

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bus Vide Experimental Researches concerning the Philosophy of Permanent Colours." By Dr. Bancroft.

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If is, I believe, computed that British India supplies three-fourths of all the indigo brought into European markets. hose Real right bas sib9q

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combined assistance of theory and practice, should lead such, at least, to question the propriety of their hatred to all theore tical knowledge. The tendency of scientific information, as it lays open causes and effects, is, to point out what parts of the process are superfluous, and what may be improved; and," in proportion as science advances, all the principles become less complicated, and, consequently, more useful; and it is then that their application is most advantageously made to the arts*" In the following remarks, I shall endeavour to bear in mind the comparative value of both theory and practice. There will be no occasion for me to make remarks upon the botanical characteristics of the indigofera tinctoria, as they are already so well known. Upon the mode, however, of manufacturing, or rather of separating, the valuable dye from the indigo leaves, something, it appears to me, need be said; inasmuch, as in works written professedly upon this subject, I have only met with one method of conducting this process, namely, the green or fermenting process; by which is intended the fermentation of the plant fresh cut and green in vats perly prepared for the purpose. There is another method the very reverse of this, the production of indigo from the dried leaves of the plant without fermentation; and this is the method which is to be the subject of the following remarks.

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I shall slightly touch upon the cultivation and growth of the plant, making a few observations on its peculiar structure, and its wonderful adaptation, both to the climate and the soil in which it is destined to exist.

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Immediately after the great periodical fall of takes place during the monsoon months of the latter part of October, November, and the beginning of December, the D107 901 10 ground is ploughed up and properly prepared for the reception of the seed. The time of sowing will, of course, depend o local situation the elevated parts sowed before the monsoon has quite passed by, while, from fear of inundation, the low tracts remain untouched till a later period.

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The plant requires a light soil, little but timely rain, and

* Vide "Elements of Agricultural Chemistry." By Sir H. Davym 104See the botanical characters of the indigofera genus in Rees's Cyclopedia, and their classification by Dr. Bancroft. quod obat a la

much sunshine. Rain should fall immediately after the plant shows itself above the ground, for by it the plant is not only invigorated, but cleansed from those innumerable insects, which otherwise would have fed upon, and destroyed the leaves. From this time, comparatively little rain is required, if it fall opportunely, that is at the different stages of the growth of the plant. After the first cutting of the branches, it sickens, and at that period rain is particularly necessary for its proper restoration. The same remarks will, of course, apply to the like periods between the other cuttings.

This plant, unlike the Bengal plant, is only made use of for one year, during which the branches are cut off from the stem three or four times, after which the ground is ploughed up for another sowing. But each successive growth of the branches produces an increased deterioration of the qualities of the leaves; so that one part of the leaves of the first cutting would yield as much indigo as two parts of the third crop.

The produce of the leaves is very precarious, for excessive rain is almost as destructive of the properties of the plant, as continued drought is of the plant itself. The rapidity of the growth of plants during much rain, in the temperature of the tropics, is extraordinary, and a proportionate deficiency in all that characterizes the vegetable world necessarily follows. This we find to be the case with all forced vegetables; and the mildness of the radish of hastened growth, when contrasted with the highly pungent and almost acrid flavour of the slowly and gradually advanced one, may be adduced as explanatory of this observation. Besides this general remark, however, there are other considerations in some measure peculiar to this plant. Indigo contains an extraordinary quantity of carbon, to obtain more or less of which carbonic acid gas must be decomposed; the plant retaining the carbon, and transpiring pure oxygen gas*. But as this important change can only be effected

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*There are, indeed, some plants which must derive the whole of their carbon from the atmosphere. Sir H. Davy remarks, Many plants that grow upon rocks or soils containing no carbonic matter, can only be supposed to acquire their charcoal from the carbonic acid gas in the atmosphere." In the sandy soil of India there certainly cannot be enough of vegetable matter to supply a proper proportion of carbon.

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when the plant is under the direct and immediate influence of light, rainy weather, by intercepting the sun's rays, prevents the accomplishment of this very important part of vegetable economy. Hence it is, as it is practically well known to manufacturers, that the indigo plant, however fine and luxuriant, as is the natural result of much rain, is very deficient in produce, and a similar loss is experienced even if the plant, without the fall of too much rain, has grown up under cloudy weather. Sunshine, much and continued sunshine, is essentially necessary for the proper exercise of those secretory organs by which this peculiar drug is formed and perfected.

This plant is destined, therefore, to exist under a burning sun and much deficiency of rain; how then is it to obtain its necessary supply of water? Nature, who invariably so well adapts the means to the end, has, in this instance, displayed her usual wisdom. The root, instead of being short, and branching off in different directions, and reaching to various depths, is one continuation of the stalk, which, decreasing gradually to a point, after the manner of the common garden radish, descends perpendicularly into the ground, to the depth of about three feet. While, therefore, the plant is necessarily exposed to the continued heat of a broiling sun, it is deriving benefit from the moisture of that part of the soil, which always remains uninfluenced by any external heat. I before stated that the nature of the soil should be light and sandy; and the nonconducting powers of the sand, in reference to caloric, afford a sufficient reason for the complete protection of the root. I have often found that, while the surface at mid-day was too hot to allow the hand to remain in contact with it, the temperature of the sand, at even a short distance beneath the surface, was gratefully cool*.

There remains another reason why the plant can endure drought so continued. As dew is the condensation of the

A good instance of the non-conducting power of sand is given in the following extract :-"The red-hot balls employed by the garrison of Gibraltar to destroy the Spanish floating batteries, were carried from the furnaces to the bastions in wooden barrows, with only a layer of sand interposed, and this was found sufficient to prevent the balls, though in a high state of incandescence, from setting fire to the wood."-TILLOCH'S Philosophical Magazine.

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