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with the air, with a solution of cane sugar, which dissolves the litharge very well, and absolutely takes nothing from the sub oxide of lead.

The nitric, sulphuric, hydrochloric, and acetic acids, feeble or concentrated, do not form distinct salts with the sub oxide of lead; they change it into metallic lead, very finely divided, and into ordinary oxide, with which they combine.

The nitrate of lead

The soluble alkalies act in the same manner. itself changes it into protoxide of lead and metallic lead. It disappears in a diluted solution of this salt, and the liquor filtered boiling, leaves deposited a mixture of nitrate and of basic nitrate of lead.

Mixed with a small quantity of water, in contact with the air, the sub oxide of lead acts in a remarkable manner, and of which we do not find any reasonable explication, except by admitting that it really constitutes a definite compound.

It then produces much heat, rapidly absorbs the atmospheric oxygen, and becomes converted into a white powder, which is the ordinary hydratic oxide. A mixture of lead, very finely divided, and litharge in a fine powder, produces nothing similar.

Heated to a dull red the sub oxide of lead becomes decomposed, and forms a mixture of lead and its protoxide. We recognise this decomposition with facility, whether by amalgamation, or with boiling sugar water, which dissolves the oxide, or with feeble acetic acid, which leaves a residue of lead, which in place of being in a fine powder, as with the sub oxide, presents itself in net work, which needs only to be compressed between the fingers to become a compact mass of a metallic aspect.

Besides, the mixture is immediately distinguished from the sub oxide by its colour, which is yellow, slightly tinged with green.

The tribasic oxalate of lead is decomposed by heat, like the neutral oxalate; but the gases vary in their relations during the whole length of the operation, and the residue is a mixture of the sub oxide and of protoxide. I was assured of this upon using a boiling solution of sugar, which dissolved a considerable quantity of the protoxide of lead.

The analysis of the sub oxide of lead has not in any manner to be made after the examination of the relation of the gases proceeding from the oxalate.

This relation sufficiently indicates for the sub oxide the formula Pb20, which likewise confirms the properties of this compound.

100 parts of sub oxide heated in contact with the air, have given 103,7 and 103,6 of the protoxide.

This oxidation is effected with great facility, for the sub oxide of lead is pyrophoric, and when we heat it in a weight of its mass, the whole mass entire takes fire.

The incontestable existence, however, of the sub oxide of lead is important for the general history of the combinations of oxygen with the metals. This sub oxide will doubtless not remain long the only one of the species, but it will soon place itself at the head of a

series of compounds which will present, with the superior degrees of the oxidation of the metals, this very singular point of resemblance, that neither one nor the other can combine with the acids.

The oxalate of zinc gives from the dry distillation, the ordinary oxide of zinc, and sensibly too, equal volumes of carbonic acid gas and oxide of carbon.

That of copper is decomposed with the greatest facility; it sets at liberty carbonic acid almost pure, and gives a residue of copper quite metallic, in scarlet spangles, brilliant and malleable, some of which are several millimetres broad, although they certainly proceed from a pulverulent and amorphous matter, which has not been submitted to any fusion.

On the Theory of the Fabrication of Carbonate of Lead (ceruse). -The process for the fabrication of white lead, by M. Thenard, is well known, and was for the first time executed by M. Rouard, in his domestic economy of Clechy. This process, known under the name of the French process, to distinguish it from another kind of fabrication employed at first in Holland, consists in making carbonic acid pass into a solution of tribasic acetate of lead. This latter salt cedes to the carbonic acid the two of its base, which it deposits in the state of white lead, and thus becomes neuter. It may serve anew for the same operation, after its having combined directly with the oxide of lead. We conceive that a considerable quantity of ceruse may thus be produced, by a comparatively very feeble proportion of acetate of lead, and consequently by acetic acid. There would even be no limit to the production of ceruse with the same vinegar, if this salt did not retain a feeble quantity of acetate of lead.

A modification has been projected in England of the process of M. Thenard, by which they have, if I may so express it, transformed it into a process by the dry method. This process consists of mixing with litharge about the hundredth part of its weight of acetate of lead, and to cause to pass on the mixture, previously wetted with a very small quantity of water. In a few hours all the litharge is carbonated, and the operation is finished.

Carbonic acid and oxide of lead, alone, are only united with extreme slowness. It is necessary then to admit, that the some thousandth parts of acetic acid, which are found in the preceding mixture, are conveyed over the entire mass of oxide of lead, to constitute a basic ascetic, which is destroyed and re-produced without cessation. That process named the Holland one, which was transported many years ago to Lille, where it has become a very important object of industry, consists in exposing the plates of lead to the vapour of vinegar and to the exhalation arising from horse dung. vinegar made use of is that made from beer of an inferior quality, and which contains a very small quantity of real acetic acid. After an examination which I made of this vinegar, for which I am under considerable obligations to the courtesy of M. M. Lefevre and Decoster, manufacturers of ceruse at Lille, the weight of the real

The

acetic acid does not amount to the one hundred and fiftieth part of the weight of the lead, and we know that in good operations almost the whole of the lead is transformed into ceruse. M. Graham has arrived at similar conclusions in England: he has even found less acetic acid than I have, relatively to the weight of the lead.

It is impossible then that the carbonic of ceruse proceeds from the decomposition of the vinegar.

The manufacturers, on the other hand, well know that they cannot obtain ceruse except they establish with care currents of air in the mixtures above spoken of.

The theory of this fabrication is very simple then, and similar to that of the other processes of which I spoken in the first place.

The oxidation is caused by cold air, and the vinegar, in vapourising under the influence of considerable heat produced by the fermentation of dung, unites with the oxide of lead, from whence it is soon displaced by the carbonic acid disengaged in abundance by the dung. In the unwashed Holland ceruses, a great portion of the acetic acid is recovered.

I believe that such is the manner in which these things take place; and during the ten years since I have left Lille where I was enabled to study this fabrication, I have always presented this theory as being the most rational. At this epoch, almost every chemist thinks that the carbonic acid co-operates with its elements to the composition of ceruse.

I have made an experiment which shows plainly the part which vinegar takes in the fermentation of ceruse. I composed an artificial atmosphere of oxygen and carbonic acid, and I abandoned to itself in this atmosphere, a plate of lead placed over a vase containing vinegar. At the end of three months, the plate of lead had become converted into a white crust of ceruse. The proportion of this was such as to indicate that the oxygen and the carbonic acid were absorbed. Almost the sum total of the vinegar was found. The proportion which had served to determine the formation of the ceruse was so small, that it could not be estimated.

Another very curious experiment shews very well, in my opinion, the true part which the acetic acid acts in the formation of ceruse, and the necessity of introducing in this fabrication an acid susceptible of producing with the oxide of lead a sub salt decomposable by the carbonic acid. If in the preceding experiment we substitute formic acid for the vinegar, which does not produce, as is well known, the basic salt with the oxide of lead, it does not form ceruse, even after several years of contact between the vapours of the formic acid, the metallic lead, and the oxygen and carbonic acid gas. Formic acid, nevertheless, is very nearly allied, by its affinities to acectic acid, and volatile almost to the same degree as it, but it does not form the basic salt with the oxide of lead, and the neutral formiate of this metal is not decomposed by carbonic acid; this is the reason why its use is improper for the production of ceruse.

Atmospheric Electricity.-By Mr. THOMAS SPENCER.

SECTION V.

In every branch of human knowledge, not even excepting the strictly scientific, the propounder of a theory, among the disadvantages he has to contend with, and they are not few, runs the risk of compromising any reputation he may have hitherto gained, as well as of throwing a bar in the way of the due appreciation of future labours, although, perhaps, of unquestioned utility. Such are the general results, in the event of his views proving ultimately to be correct; one generation having to pass away, and himself with it, before they are admitted to rank with the elementary knowledge of the next. On the other hand, should they be incorrect, the consequences are disastrous, and a long life of future scientific labour is often insufficient to compensate for the one blunder.

With both these positions fully before me, I have ventured to propound my views theoretically on the subject of atmospheric electricity; but have hoped the strong facts on which they are founded will at once render them obvious even to the unscientific, and, perhaps, spare me much of what I have just predicated.

While these papers have been undergoing publication, I have received several communications on the subject from different quarters; some giving their assent; others blaming my rashness and withholding assent; and a third requiring further information, the published papers being necessarily abridged. To the latter I have replied privately; but, with respect to those who dissent in opinion, they hold my grand error to be, that I have assumed a chemical action to have taken place when water has been converted into steam, and a like action when the steam is reconverted back to water. Another objection, less easily answered, is made, that I have taken the imponderables, heat and electricity and used them as so many ponderable bodies; or, in other words, that I have taken two things that are known to exist universally in nature, but are not recognised to have substance, and are merely considered under the vague title of forces, that have no weight, and used them as chemical compounds.

To this I plead guilty, in the fullest sense of the word. Yet, be it observed, I still look on these bodies as imponderable—that is, relatively to the mass of our planet. But that they are imponderable, relatively to the mass of the centre of our system, I cannot admit. In relation to that body, they may have sufficient density to he atmospheric; indeed, unless some such state of things have existence with respect to those bodies, in relation to the sun, it is difficult to conceive how the principle of gravitation can be universal.

Hydrogen, the lightest of known bodies, on the surface of the sun would weigh twenty-nine times more than it does with us; while, at the surface of our own satellite, no reasonable doubt can exist that its ponderability would be hardly detectable by the finest conceivable

mechanism, and there, would consequently be ranked among the imponderables: yet we know its ponderability.

Voltaic, or more properly, chemical, electricity has been already considered by Dr. Hare' as a compound of another species of electricity with caloric. How far he carries his opinion, I am, at present, unaware: but, at the hazard of being deemed speculative, I may venture to say that we are borne out by analogy in supposing that the four recognised species of electrical power, namely, chemical, frictional, magnetic, and thermo-electricity, are, in all probability, compounds of one base, combined atomically with caloric in different proportions.

Speculations regarding the nature of electricity are daily becoming more interesting, although, perhaps, of questionable utility; but when we take into view the fact, that every form of matter we are acquainted with is saturated in definite proportions with this wonderful power, lying, as it were, dormant, but never, under any circumstances, refusing to be drawn forth to perform its functions when the proper means are applied; and when we recollect, that, like substances, it can never be dissipated, the force, it is true, may be misapplied by ignorance, but not wasted,-fulfilling its assigned office during its transit from one body to another, from whence it may be again and again recalled with definite, yet undiminished vigour.

With these facts before me, surely I may be pardoned in looking on electricity as something more than a mere force in nature, without substance. Dissent from these opinions does not, however, necessarily invalidate, or otherwise, what I have already promulgated on the nature and proximate origin of the electricity of the atmosphere. On the contrary, had other proofs not existed, I should never have hazarded them.

The experimental proofs of the necessary nature of cloud arise out of the following fact, discovered accidentally at the close of 1840, and since followed up with much ingenuity by Mr. Armstrong, of Newcastle, and confirmed by many others. This is the electricity that is found to exist in connection with steam.

I now quote from a communication made by Mr. Armstrong to Dr. Faraday. After describing the portion of the boiler, &c., in which the occurrence took place, he says, "About three weeks ago the steam began to escape at this joining, through a fissure in the cement, and has ever since continued to issue from the aperture in a copious horizontal jet. Soon after this took place, the engineman, having one of his hands accidentally immersed in the issuing stream, presented the other to the lever of the valve, with a view of adjusting the weight, when he was greatly surprised by the appearance of a brilliant spark, which passed between the lever and his hand, and was accompanied by a violent wrench in his arms, wholly unlike what he had ever experienced before. The same effect was repeated when he attempted to touch any part of the boiler or any iron-work connected with it, provided his hand was exposed to the steam. He next found, that, while he held one hand in the jet of steam, he

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