had used it for the towing line of his small models, as it could be strained without breaking until the deflection was only half an inch, while brass wire of the same length, &c., broke when the deflection was three inches.

Mr. West then read Mr. Shaw's paper "On a New Steam Engine worked with three kinds of pressure, viz. action of high pressure steam, the expansion of steam, and the atmospheric pressure caused by its condensation." The description was illustrated by models and drawings. The lower part of the piston fits the cylinder and is steam tight; the upper part or plunger, in the form of a hollow cylinder, is longer than the cylinder and passes through a stuffing box in its cover. The piston rod rises through the middle of the plunger, and is connected with the parallel motion: the valve is a modification of the single slide, the upper passage leading to the upper part of the cylinder, the middle to the lower part of the cylinder, and the lowest to the condenser. When the piston is descending the valve admits steam to the annular space between the plunger and cylinder, when, the middle and lower passages being open, the direct pressure of the atmosphere upon the plunger, the high pressure steam upon the annulus, and an additional pressure of one atmosphere upon the annulus from the vacuum beneath, concur to produce the down stroke; during this the steam is cut off from the cylinder, and the communication between the cylinder and condenser is shut; the steam, which before occupied the annulus, now acts against the plunger for the ascending stroke, while the whole force of expansion, the annular surface of the piston being then passive. Mr. West then described Mr. Shaw's hydraulic engine, of which a model and drawings were also exhibited. In this engine the want of elasticity in water, which formed a great objection to the application of a fluid to a piston is supplied by the elasticity of air in a chamber communicating with the cylinder; it is well fitted for situations where the fall is great, but the supply too small or the space too limited for the use of a water-wheel, as in mines.

Mr. Clegg then explained his dry Gas-meter. It acted on the principle of the differential thermometer, in which a difference of temperature between two bulbs partly filled with alcohol, was shown by the rising of the spirit in one and depression in the other. He had taken advantage of this principle by suspending two little glass vessels, partly filled with alcohol and connected by a tube, and by passing the gas over heaters, it warmed one of these bulbs, and the spirit was driven into the other, which, becoming the heaviest, swung to the bottom of the arc in which the vessels vibrate; here it, in its turn becoming warm, was emptied of its spirit, and thus becoming lightest was in its turn displaced; the continuance of these oscillations marked the flow of gas, and being registered by the usual train of wheel-work, the number of vibrations had been proved, by many careful experiments at all seasons of the year, to afford an accurate measure of the quantity of gas.

THE ANNALS

OF

ELECTRICITY, MAGNETISM,

AND

CHEMISTRY;

AND

GUARDIAN OF EXPERIMENTAL SCIENCE

DECEMBER, 1842.

Experimental Researches on a peculiar Action of Iron upon Solutions of some Metallic Salts. By Dr. C. F. SCHOENBEIN.

(Continued from page 413.)

"SOME time ago I published several papers, in which I made known some very remarkable facts regarding the action of iron upon oxygen. According to the notions generally adopted by philosophers respecting the action of metals performing the function of the positive electrode upon oxygen set free by voltaic action, iron, as one of the more readily oxidable metals, chemically combines with that element. In one of the papers alluded to, I have shown that these notions with regard to iron, do not hold good in all cases, and that this metal acquires under certain circumstances, the property of platina or gold, that is to say, that whilst constituting the positive electrode, it is neither oxidized nor otherwise chemically affected by oxyacid solutions, which usually act upon iron with more or less violence. I have further observed, that this inactivity of iron depends upon the manner of closing the circuit, as well as upon the chemical nature of the electrolytes contained in the solutions in which the polar wires of the pile are immersed. Solutions containing oxyelectrolytes which act chemically upon iron, as, for instance, sulphuric or nitric acid, require the circuit to be closed in a certain manner, in order to evolve oxygen at the positive iron. Solutions containing oxyelectrolytes which do not sensibly act upon iron, as, for instance, those of potash, soda, and a great many oxysalts, allow the evolution of oxygen at the positive iron quite independently of the manner of closing the circuit. In solutions containing, besides oxyelectrolytes, others of a different nature, for instance, hydracids, haloid salts, &c., no evolution of oxygen takes place in whatever manner the circuit may be closed. From these facts, and others stated elsewhere, I am inclined to infer that the affinity of iron for Ann. of Elec. Vol. IX, No. 54, Dec., 1842.

Gg

oxygen is destroyed by a current moving through the metal in a certain direction, and that the affinity lost in this way by the iron is revived by an opposite current. To ascertain whether this view holds good generally with regard to iron, I have made a series of experiments, the results of which are as follows. I introduce an iron wire which had previously been connected with the positive pole of a small battery, into an aqueous solution of the common sulphate of copper, by means of which the circuit was closed. According to my hypothesis, no action whatever is to take place on the part of the iron upon the solution, under the circumstances here stated. My expectations were fully realized, for after many hours' action of the pile, not the smallest particle of copper was deposited on the iron wire, its surface had not undergone the least change, and during the whole time of action oxygen was evolved at the iron. But as soon as the passage of the current through this metal was opposed only for a moment, for instance, by taking out of the copper solution either the negative polar wire or the positive one, there appeared on the surface of the latter a film of copper. The same result was obtained by joining momentarily the two polar wires within the solution, or by touching the iron wire with another metal capable of precipitating copper.

:

"Now, by these facts I think two things are clearly shown: first, that iron ceases to have any affinity for the oxygen both of the oxide of copper, and of the water decomposed by voltaic action: and secondly, that this state of chemical indifference lasts only so long as there is a current passing from the iron into the copper solution. This influence of current electricity upon the chemical bearings of iron is highly interesting, not only on account of its being contrary to the electro-chemical notions hitherto entertained on the subject, but also on account of the circumstances under which the oxygen resulting from the decomposition of water is presented to iron. These circumstances are, indeed, of such a kind as highly to favour the oxidation of the metal, for oxygen in a nascent state is brought into contact with iron and there is at the same time a portion of the acid of the salt set free by voltaic action at the iron wire, which also tends to occasion the oxidation of the latter. The same remarks apply to the fact already stated, that iron is not acted upon by nitric or any other oxyacid, provided this metal is placed under the influence of the pile in the manner above mentioned. Iron, however, may acquire the property of being not acted upon by nitric acid or solutions of certain metallic salts without being subjected to the influence of a current. This remarkable fact has been observed by Sir John Herschel, and more recently by Mr. Faraday and myself. If, for instance, a common iron wire, having been made inactive by repeated immersions in common nitric acid, is put into a solution of blue copper vitriol, not the least chemical action takes place. It is true that it happens sometimes that such a wire precipitates copper at the moment of its being plunged into the

The

solution, but in such a case the inactive state of the metal had ceased previously to immersion. Now whether iron is or is not in its peculiar condition may easily be ascertained by the appearance of the surface of that part of the wire which had been immersed in nitric acid. If the surface is bright, the wire is inactive; if yellowish brown, the metal has assumed its common state, and will consequently act upon the copper solution in the usual manner. peculiar condition of iron with regard to the copper solution can be destroyed in different ways. In the first place it may be destroyed by making an inactive iron vibrate. If such a wire is wetted by the said solution, and afterwards rather violently struck against any solid body, for instance against a table, immediately after the shock a film of copper will make its appearance along the whole wetted surface of the wire. According to the results of my experiments, published in several periodical works, inactive iron is rendered active with regard to nitric acid by the same means. In the second place the active state of iron may be reproduced by touching the inactive metal with a metal which acts chemically upon the solution of the copper salt. If an inactive wire is wetted by this solution, and then touched on any point of the part wetted, with a piece of common iron, zinc, cadmium, tin, lead, arsenic, or even copper, the precipitation of copper instantaneously takes place at the point of the iron wire where contact had been effected, and this action rapidly extends itself over the whole part of the wire which is covered with the solution. It is a matter of course that the same effect can be obtained by touching the inactive iron wire within the solution of the copper salt with the same metals. But the peculiar condition of iron may be changed into the common state without immediately touching those parts of the metal which are surrounded with the copper solution. If, for instance, an inactive wire is put into the solution, so as to allow part of it to rise above the level of the fluid, and if a wire of any of the metals above mentioned is placed in the same solution, having likewise one of its ends raised above the surface of the liquid, copper will be precipitated as soon as the free ends of both wires are made to touch one another. This mode of changing the state of iron is exactly the same as that by which a similar change of condition of this metal may be effected with regard to nitric acid. Now, all these facts evidently prove that the peculiar condition of iron, whatever the cause of it may be, is always destroyed by the chemical action of metals brought into contact with iron when in the inactive state. There is certainly one singular fact, which seems to indicate as if contact independently of and unconnected with chemical action could of itself occasion a change of state in iron. It has been already stated, that copper brought in some of the ways mentioned into contact with an inactive iron wire, which is immersed in the copper solution, renders the latter metal active. Now copper of course cannot be precipitated from the solution of blue vitriol by copper the chemical action of this metal upon the copper salt must,

therefore, be essentially different from that which is exercised by the more readily oxidable metallic bodies in question. First, I thought there might, perhaps, be some free acid contained in the solution, and by this means chemical action occasioned. To ascertain the correctness of this view, I added ammonia to the solution until flakes of oxide of copper were beginning to make their appearance; but the copper wire acted in such a neutral solution in the same manner as it did in the more acid one; chemical action consequently does not result from the cause supposed. I think there is only one way left to account for the fact in question. It is well known that copper put into a solution of a salt containing the deutoxide of this metal, unites by degrees with this base, to form protoxide of copper. Although this chemical action is extremely slow and weak, still it is of sufficient power to revive in the inactive iron its dormant affinity for oxygen.

"There is no doubt that, one case excepted, in all others hitherto mentioned, in which passive iron is rendered active, an electric current is produced, passing from the metal in which chemical action originates, through the solution, into the inactive iron, and from this back again to the first metal. It is further obvious, that the direction of the current passing through the inactive iron is opposite to that in which the current moves through an iron wire which performs the function of the positive electrode of a pile. The chemical effects produced upon iron by these different currents being also the reverse of one another, it seems to me that these facts speak in favour of the idea already suggested, that the chemical affinity of iron for oxygen is destroyed by one kind of current, and called forth again by the other. It is true, one of the most sagacious philosophers of the age, Mr. Faraday, has started an idea which seems to account very satisfactorily for the phenomena in question. According to this view the peculiar condition of iron depends either upon a film of oxide covering the metal, or upon a relation of oxygen to iron equivalent to oxidation, so that the particles forming the surface of the inactive iron have satisfied in one way or other their affinity for oxygen. Applying the same hypothesis to account for the bearing of iron in the solution of blue vitriol, which Mr. Faraday has made use of for explaining the singular action of iron upon nitric acid, we must say, an inactive iron wire does not act upon the solution of the copper salt, because there is no immediate contact between the truly metallic particles of the wire and the said solution, on account of the interposing film of oxide, or something similar to it. But if now another metal be put into the solution, which is chemically acted upon by the latter, there is a current produced, proceeding from the active metal, and passing through the solution into the inactive iron. By this current water is decomposed, hydrogen evolved at the iron; the film, or what is equivalent to it, deprived of its oxygen; and by this means a truly metallic surface of the iron wire produced. Though this way of accounting for the facts in