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gas; but with the last, the fusible protoxide being used, butter of antimony is produced, and carbonic oxide libe rated, and an infusible peroxide formed, a proof, if any was required, of the formation of carbonic acid in the preceding instance being owing to the decomposition of the oxide of zine, and not of the oximuriatic gas.

These are some of the principal circumstances I have discovered respecting this new gas; a gas, which, as it reddens litmus and expels acids from ammonia in consequence of superior attraction, has every claim to be considered as a peculiar acid singularly composed of two acidifying prin ciples united to one inflammable base.

After the preceding statement of facts, Mr. Murray, I should conceive, will be induced to renounce his conclusion, "that the production of carbonic acid in his experiment was established beyond the possibility of doubt;" and admit, that what he considered as carbonic acid was actually the new gas just described; and I should likewise imagine, that this gentleman in future will be more cautious in his assertions, and criticisms on the labours of others. Let the intelligent candid reader judge of the propriety of the following observation. Mr. Murray says, having previously stated, that he had found carbonic acid in all his experiments, "that the Messrs. Davys did not obtain it in theirs, because they did not look for it with sufficient care, or were not sufficiently aware of the fallacies, by which its production might be concealed." His considering the new gas as carbonic acid is another instance of the evil tendency of attachment to hypothesis. How just is the remark of Lord Bacon! quod mavult homo esse verum, id facile credit.

In a former communication I have observed, that no carbonic acid appeared to be formed, when dry carburetted hidrogen and oximuriatic gas are inflamed by the electric spark, assigning as a reason for this belief, the precipitation of charcoal. I tried both olefiant gas and carburetted hidrogen procured by the decomposition of acetate of potash by heat. Mr. Murray says, that he has repeated the experiment, and that in this too I was deceived. Mr. Murray employed the gas produced by heat from moistened charcoal.

charcoal. It is surprising that he is not aware, that Dr. Henry found this gas to be a mixture of carburetted hidrogen and carbonic oxide; and that the formation of carbonic acid might be expected on passing a mixture of it and oximuriatic gas frequently through lime water, as he experienced, this being the result when a mixture of pure carbonic oxide and oximuriatic gas is thus treated.

There is nothing farther in Mr. Murray's communications, that requires notice, excepting a misuse of names. He sometimes writes properly, calling me "Mr. J. Davy," at other times, improperly "Mr. Davy," thus creating ❤ confusion, and rendering it impossible to distinguish opinions and statements which belong to me, and for which I alone am answerable, from those of Mr. Davy, my brother.

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Method of preparing a beautiful and permanent White for
Water Colours. In a Letter from Mr. GROVER Kemp.

SIR,

IT is

To MR. NICHOLSON.

cate all we can

T is a very just remark of the ingenious and candid Chap- It is our duty tal, that, "at a time when the minds of all men are bent to communion confirming public happiness, every citizen owes to his to the publie country all the services that his situation allows him to accomplish; he should be eager to pay to society the tribute of those talents with which Heaven has favoured him; and there is no one who is not able to bring some materials to the foot of that superb edifice, which a virtuous government is erecting to the happiness of all *:" and believing with this

See "Elémens de Chimie par M. Chaptal," Montpellier edition, 1790. Advertisement, p. 5.

VOL. XXX.-SEPT. 1811.

D

celebrated

white for water colours.

A permanent celebrated chemist, that it is the duty of every one to do what he can towards the advancement of general science, I am induced to lay before the public, through the highly respectable medium of the Philosophical Journal, a new and easy method of preparing a beautiful permanent white for water colours, calculated to stand the test of time; which, I understand, is at present a great desideratum among our artists. This being the case, I entertain a confident hope, that the present discovery may prove eminently useful.

Mentioned by

Mr. Hume.

Through the information of a chemist of the name of Hume, the public is already in possession of the facts, that a colour can be prepared from barytes; and that this earth will furnish the only white for water painting, that never changes; which may also be mixed with any other colour without injury; but of its mode of preparation we have hitherto, I beheve, remained entirely ignorant. This beautiful pigment, which not only surpasses in opacity and whiteness every thing of the kind I have ever met with, but possesses the peculiar advantage of being permanent, is prepared by the following simple process: Dissolve pure barytes, or the common native carbonate, in diluted nitromuriatic acid; filter the solution, and add thereto as much carbonate of ammonia, previously dissolved in distilled water, as is sufficient to precipitate the earth; which may be separated by filtration, and, after repeated washings with distilled water, must be gradually dried by the heat of the sun, or a fire, and rubbed into a very fine powder, or made up into cakes for use. I decomposed some nitro-muriate of barytes with a solution of pure ammonia, but the precipitate was very inferior in colour to the above. An artist of ace knowledged celebrity, who has used this white, speaks very encouragingly of it.

Brighton, 8th mo. 4th,

1 remain, respectfully,

GROVER KEMP.

1811.

VII.

The Natural History of Clouds. By LUKE HOWARD, Esq.

A CLOUD is a visible aggregate of minute drops of

water suspended in the atmosphere.

the term cloud.

The word is probably derived from the Anglo-Saxon ceh Etymology and los, covered, kidden, the face of heaven being so in those definition of parts where clouds appear. The same aggregate, which in this situation is called cloud, obtains the name of mist, when seen to arise from the earth or waters; and fog, when it envelopes and covers the observer. Yet the two latter, viewed from a greater distance or elevation, present all the appearances of clouds; while these, in their turn, become mists and togs, in proportion as we approach and penetrate them. It may be proper, therefore, for the sake of preci sion, that the term cloud, in philosophical language, should be made a general one, comprehending all such aggregates, however situate.

It is concluded, from numerous observations, that the Formed of particles of which a cloud consists are always more or less drops of water. electrified. The hypothesis, which assumes the existence of

vesicular vapour, and makes the particles of clouds to be hollow spheres, which unite and descend in rain when rup tured, however sauctioned by the authority of several eminent philosophers, does not seem necessary to the science of meteorology in its present state; it being evident, that the buoyancy of the particles is not inore perfect than it ought to be, if we regard them as mere drops water. In fact they always descend, and the water is elevated again only by being converted into invisible vapour.

Natural History of Clouds.

Since the general introduction of accurate instruments for Prognostica. determining the changes of density, temperature, humidity, ther from

* This valuable paper was first inserted in Mr. Tilloch's Philosophical Magazine, and reprinted, with the author's revisions, in Dr. Rees's New Cyclopedia, article CLOUD, from which I have copied it, in order that the readers of our Journal may more completely understand the Mete Brological Tables, which will in future appear in our work. W. N.

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tions of wea

them.

Modifications of Clouds.

and electricity, which continually occur in the atmosphere, our knowledge of its constitution and properties has been considerably advanced. It is nevertheless true, that the philosopher of the present day is not more weather-wise than his predecessors in ancient times. He is still obliged to yield the palm in the science of prognostics to the shepherd, the ploughman, or the mariner; who, without troubling his head about the reasons of things, has learned, by tradition and experience, to connect certain appearances of the sky with certain approaching changes; of which those appearances are, in fact, a commencement or continuation, discoverable while the cause is yet at a distance. Undoubtedly the union of these two kinds of knowledge would best deserve to be entitled the science of meteorology; and it must tend, equally with the invention or perfection of philosophical instruments, to the improvement of this science, could we restore to its place the ancient and popular branch of it, now too much neglected by philosophers, which is founded wholly on natural phenomena. If we except the changes of the wind, some indications of moisture and dryness, and a few others of less importance, the whole of these may be traced fo one common origin in the product resulting from the decomposition of vapour; which remains, during a certain interval, in a state of simple diffusion or suspension in the atmosphere. To give to the extensive collection of facts, which it is easy to make on this subject, a communicable and useful form; to render that attainable in a short time, which has been hitherto the exclusive treasure of the adepts of long experience, is the object of the writer of the following systematic nomenclature and natural history of clouds.

Clouds are susceptible of various modifications.

By this term is intended the structure or manner of aggregation, in which the influence of certain constant laws is sufficiently evident amidst the infinite less diversities resulting from occasional causes.

Hence the principal modifications are as distinguishable from each other, as a tree from a hill, or the latter from a fake; although clouds, in the same modification, compared

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