Abbildungen der Seite

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.


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 be 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

communicated a shock to every person he touched with the other, whether such person were in contact with the boiler, or merely standing on the brickwork which supported it; but that a person touching the boiler received a much stronger shock than one who merely stood on the bricks.” Mr. Armstrong made some further experiments, all of them tending to confirm his first observations; but, being unable to account for these appearances, he committed their results to Dr. Faraday. This gentleman suggested a number of experiments to Mr. Armstrong; and, in his remarks on the nature and origin of electricity discovered to exist in steam, says, “ The evolution of electrictity by evaporation described by Mr. Armstrong is, most likely, the same as that already known to philosophers, but on a much smaller scale, and about which there are, as yet, doubts whether it is to be referred to mere evaporation, as Harris says, or to chemical action, according to others. This point neither settles nor illustrates; but it gives us the evolution of electricity during the conversion of water into vapour upon an enormous scale, and, therefore, brings us much nearer to the electric phenomena of volcanos, waterspouls, and thunderstorms than before.The electricity alluded to by Dr. Faraday as being already known to philosophers has, in reality, as much relation to the electricity proceeding from the conversion of steam into water, as light has to darkness, inasmuch as the negative state was already known, or, more properly, suspected, when water was being converted into steam, but the positive electricity discovered on this occasion was never before detected under the same circumstances.

Positive electricity is the only electricity, negative electricity being the appellation given to a state of things where it does not exist, or just as we speak of cold as being the opposite of heat.

The proofs we have of the existence of that peculiar state of things termed negative electricity, in connection with evaporation, are illustrated in the following simple experiment :-Adjust a platinum crucible, containing a little water, on the brass ball or plate disc of a common gold leaf electrometer, then add a red hot cinder to the water contained in the crucible, which will cause evaporation to take place, and, at the same time, the gold leaves will be distended towards the sides of the instrument. This action of the leaves points out to us that when water is being converted into steam, in other words, evaporated, that electricity is absorbed. Not only is electricity absorbed during the progress of evaporation, but I am led to infer further, that it is essential to the process itself. Since this paper was read in Liverpool, a paper has been published in the Philosophical Magazine detailing an experiment which goes very far to prove this. The writer, Mr. Rowell, took two cups of water, each containing eight ounces.

One of them was made to commu. nicate with the earth by means of a copper wire: the other was what electricians term insulated, having no metallic communication with the earth. They were both placed in otherwise equal circum

stances in a warm room over an oven. In twenty-five hours the cup, having electrical communicatiou with the earth, had evaporated fourteen dwt. and nine grains more than the one having no communication. I have repeated a similiar set of experiments, and with nearly similar results, always, at least, showing an excess in favour of non-isulated vessels of water. I may here state that the writer, in the same communication, briefly says, he has entertained views somewhat similiar to some of those I have published in the foregone sections, and that he has entertained them since 1840. As he will, in all probability, publish them in detail, at present I can only say my own views on the same subject were far from being matured until a later period.

In the paragraph above quoted from Dr. Faraday, it is also worthy of remark, that he at once seemed to perceive the necessary connection that existed between the electricity given out by the steam and the electrical phenomena of the heavens.

In the first experiments made by Mr. Armstrong, he was led to imagine, that, if electricity was given out with the steam at a small aperture of the boiler, it would, in all probability, exist in much larger quantity in the interior. Of course, with the views I have explained, namely, that its existence in the free state was caused by the conversion of the steam into water, it was not difficult to foresee, that any experiments to prove this would fail. This gentleman, however, made a series of experiments with this view, but no electricity could be elicited in the steam, while it was steam, but only when it had become water was this force perceptible.

From the results of these experiments, it is scarcely possible not to view them as principles that may not prove unimportant in the great business of life, but more particularly with reference to the economy of steam-engines. We thus see evaporation, or the formation of steam promoted by metallic conducting substances, on the one hand, and, when about to be condensed, on the other; there can be little doubt that a like conducting substance to carry off the electricity generated during the process would also facilitate it. I have no means of making such an experiment on the proper scale; but, where even a small saving of fuel might be the result, it is worthy of consideration, and I should be but glad to hear of such experiments being made.

With respect to the application of these results to the electrical phenomena of the atmosphere, I trust they are, by this time obvious. Still, I may be permitted to repeat, that the air, at all times, conlains a very large proportion of steam, invisible to the eye, and, hence, termed transparent aqueous vapour. From the water contained in this steam is formed cloud, rain, hail, and snow. The accidental result observed in the steam-boiler, at Newcastle, shows us clearly, that, when steam is condensed, it gives out electricity. Cloud, then, is admitted on all hands to be the condensed steam of the atmosphere. I now ask, will it not give out electricity ? or, I may add, is this phenomenon to be peculiar to the immediate sur

« ZurückWeiter »