tions, and supplied with sufficient oxygen for complete com bustion.

When the hydrogen bore a small proportion to the olefiant gas, a platinum-ball or the pure metal had no more effect than when no hydrogen was present.

When equal parts of these gases were present, a platinum ball had very little effect when cold, but if introduced when heated till it could be barely held in the hand, it caused a copious deposite of dew, with rapid diminution of volume. The residue was explosive.

A cold platinum-ball had very little effect when the olefiant gas was to the hydrogen as 1: 2, but if gently warm it acted vigorously, and I have thus obtained even the entire consumption of the inflammable mixture, though this effect cannot be relied on.

A platinum-ball, strongly heated, was put into a similar mixture, containing olefiant gas and hydrogen in the proportion of 1 3. It caused a dense deposite of dew at the moment of its introduction, became red hot, and set fire to the mixture, which exploded with great violence.

ments.

Carbonic oxide gas was made the subject of similar experiA platinum-ball was put into a mixture composed of equal parts of this gas and oxygen, without any immediate effect some diminution had taken place in the course of a few minutes, which was not much greater in twenty-four hours. A little carbonic acid had been formed, however, on the absorption of which, the residual gas was found strongly explosive. Pure spongy platinum acted in a similar manner. Balls No. 1. and 2. were brought in contact with different portions of a similar mixture, soon after they had ceased to be red hot. Rapid diminution succeeded, and carbonic acid was formed abundantly, but the residual gas was still explosive.

Spongy platinum was made red hot, and immediately after ceasing to be luminous, was covered by a jar of a similar mixture. The redness quickly reappeared, and the moment it did so, the gas exploded. Sir H. Davy has shown that a mixture of carbonic oxide and oxygen is inflamed by a heat considerably lower than is required by an explosive mixture of oxygen and hydrogen gases, a fact with which the preceding experiment entirely corresponds.

Mixtures of carbonic oxide, hydrogen, and oxygen, were made in different proportions, and brought in contact with platinum at various temperatures. The results of these experiments, however, are so nearly analogous to those already

related, that I need not give them in detail. Small quantities of hydrogen are not rendered obvious by the platinum; and the whole of an explosive mixt' re is not consumed, unless the hydrogen bear a large proportion to the carbonic oxide, and the ball be heated.

It appears from these experiments, that platinum can give us no aid in separating these different gases from one another. They shew, however, one very singular fact, namely, that great as the power of platinum is in effecting the combination of oxygen and hydrogen, the presence of certain gases has a very extraordinary influence, in diminishing that power. This observation has naturally led me to inquire into the causes which influence the action of platinum;-an inquiry intimately connected with the direct object of this paper, but which I have undertaken, not only on that account, but likewise with the design of drawing a parallel between platinum and electricity, relative to their action on explosive mixtures. [To be continued.]

ART. XXV. A discriptive Account of the several Processes which are usually pursued in the Manufacture of the Article known in Commerce by the name of Tin-Plate. By SAMUEL PARKES, F. L. S. &c. Abridged from a paper read before the Philosophical Society of Manchester.

ENGLISH bar-iron of the finest quality, called tin-iron, and which is generally prepared with charcoal instead of mineral coke, and made with the greatest care, for this particular purpose, is first cut to the necessary length, and then rolled at the mill, by a process which is peculiar to this manufacture, into plates of the requisite thinness, and of such form as is suitable for the business. These plates are then cut by hand-shears to the sizes suitable to the different markets. And as the shearer shears the plates, he piles them in heaps, Occasionally putting one plate the cross way, to keep each box separate. Two hundred and twenty-five plates are called a box, but they are not put into boxes of wood in this stage of the operation. The iron plates now go into the hands of the scaler, who takes them from the shear-house, and bends each of them singly across the middle, into this form A, preparatory to their being cleaned for tinning, and for the con

veniency of putting them into the scaling furnace, as will be more fully explained hereafter.

This furnace, or oven, is heated by flame thrown into it from a fire-place of a peculiar construction, and it is this flame that scales the plates, which are put into the oven in rows, and arranged three in each row, until the oven is full. It will be obvious that if they lay flat on the floor of the oven, the flame could play only on one side of each plate, whereas, by being bent in the form already described, the flame can operate equally on both sides. It may here be remarked that the form of all tin-plates, one sort excepted, is that of a parallelogram, and that if a piece of stiff paper, or paste-board, 13 inches long, and 10 inches wide, be bent in the centre at an angle of about sixty degrees, and then put to stand on the two ends, we shall have the form of a plate No. 1. properly bent for the scaling oven.

The operation of cleansing, as it is called, and which is preparatory to the process of scaling, is commenced by steeping the plates for the space of four or five minutes, in a mixture of muriatic acid and water, in the proportion of four pounds of acid to three gallons of water. This quantity of the diluted acid will generally be sufficient for eighteen hundred plates, or eight boxes of 225 plates cach.

When the plates have been steeped for the time prescribed, they are taken out of the liquor, and placed upon the floor, three in a row, and then by means of an iron rod put under them, they are conveyed to a furnace heated red-hot, where they remain until the heat takes off the scale, the removal of which was the object in submitting them to that high temperature.

When this is effected, the plates are taken to a floor, where they are suffered to cool-they are then straightened, and beaten smooth upon a cast-iron block. The workman knows by the appearance of the plates during this operation, whether they have been well scaled-for if they have, that is, if the rust or oxide which was attached to the iron, has been properly removed, they will appear mottled with blue and white, something like marbled paper. The operation we have been describing is called scaling.

As it is impossible the plates can go through this process without being in some measure warped, or otherwise disfigured, they are now rolled a second time, between a pair of castiron rollers, properly hardened and finely polished. This operation makes both sides of the plates perfectly smooth,

and imparts a sort of polish to their surfaces. These rollers are each about 17 inches long, and 12 or 13 inches in diameter-but I am inclined to think that if the diameter was greater, they would set the plates flatter, and do the work better in every respect.

The technical name of this apparatus is rolls, not rollers. All the rolls which are employed in rolling plates, either hot or cold, in this manufactory, are hard rolls-and there is ast much difference between a pair of hard cast-iron rolls, and a pair of soft rolls, although they may both be run out of the same pot of metal, as there is between iron and steel. The workmen inform me that the difference is entirely occasioned by the manner of casting them--the soft rolls being cast in sand, whereas the hard rolls are formed by pouring the metal into a thick cast-iron box-and that the metal, by coming in contact with the cold box is sufficiently chilled to render the whole face of the roll entirely hard. The difference in the temper of these two kinds of rolls is so great, that when they are put into the lathe to be turned perfectly true, the turnings from the one will be 4th of an inch in thickness, whilst the turnings which come from the other are not larger than very fine needles. The temper of cast-iron thus varying according to the nature of the mould into which it is poured, is a circumstance that appears to me to be deserving of attention in the manufacture of a variety of other utensils employed in the arts.

These rollers are used without heat, but they are screwed down very close one upon the other, only leaving bare room for the plates to pass, that the utmost attainable degree of pressure may be given to them. This last operation is called

COLD ROLLING.

When the plates have undergone this process, they are put one by one into troughs filled with a liquid preparation called the lies.

This is merely water, in which bran has been steeped for nine or ten days, until it has acquired a sufficient acidity for the purpose. The design of putting the plates into the troughs, singly, is, that there may be more certainty of the liquor getting between them, and both the sides of every plate being soaked alike in the lies. In this liquor they remain for ten

Since the above was written, I have submitted the manuscript to a gentleman who is very largely engaged in the manufacture of tin-plates, and he tells me that the cold rolls which are employed in his work are 30 inches in diameter.

or twelve hours standing on the edges, but they are turned, or inverted, once during the time. This operation is called working in the lies.

The next operation is that of steeping in a mixture of sulphuric acid and water, in proportions which vary according to the judgment of the workmen.

The trough in which this operation is conducted, is made with thick lead, and the interior is divided by partitions of lead. Each of these divisions is by the workmen called a hole, and each of them will contain about one box of plates. In the diluted sulphuric acid which is in the different com-. partments of this vessel, the plates are agitated for about an hour, or until they have become perfectly bright, and entirely free from the black spots which are always upon them when they are first immersed in it.

Some nicety, however, is required in this operation, for if they remain too long in the acid, they will become stained, or blistered by it, as the workmen term it; but practice enables a careful operator to judge of the time when they ought to be removed. This, however, is one of the most difficult. parts of the business, as few men like to work in it; though I understand that a good pickler is highly valued by his employers, and obtains great wages. It is necessary to notify that this, and the former process with the acidulated water, are both hastened by giving to those menstrua an increase of temperature--and this is effected by means of heated flues which run under each trough. Little additional heat is necessary in summer, however, as 90° or 100° of Fahrenheit is a temperature sufficiently high for either of these operations. When the plates come out of the pickle, they are put into pure water, and scoured in it with hemp and sand, to remove any remaining oxide, or rust of iron, that may be still attached to them, for wherever there is a particle of rust, or even dust upon them, there the tin will not fix; and they are then put into fresh water to be there preserved for the process of tinning. The design of putting the plates into pure water, after they come out of the sours, is to prevent their becoming again oxidated-for it has been found that after these operations, they will acquire no rust, although they should be kept twelve months immersed in water.

It will be perceived that all these processes are nothing more than preparatory measures for the operation which is to succeed, viz. that of TINNING.

For this purpose an iron pot is nearly filled with a mixture