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the Athenæum, Manchester, that there is no diffuse into each other, with different degrees locality in the world where a knowledge of of rapidity, which bears a certain relation to chemical laws is of so much practical ad. their specific gravity ; and hence it shows vantage as in this metropolis of manufactures, that, by availing ourselves of this tendency it was with peculiar pleasure that I lately in mixed gases, a sort of mechanical separaheard of a most interesting application of tion of the various gases may be effected. those laws, in a newly-discovered process Now, it is precisely this separation that is for burning smoke and economising fuel, by effected by Mr. _'s process—the uncon. Mr. —, by which those two important ob sumed carburetted hydrogen and carbonic jects are effected in a manner far superior to oxide are returned under the fire-grate, mixed any thing of the kind that has ever been seen with a fresh supply of oxygen ; while, at the before. The particular chemical laws thus same time, nearly the whole of the nitrogen applied are those relating to the diffusion of and heavy carbonic acid gases are allowed to the gases, and other elastic fluids, said to be pass off below to the chimney. first discovered by Dr. Priestley ; but the From a consideration of this theory, the scientific principles of which were certainly intelligent manufacturer will perceive, that, first described by Dr. Dalton, in a paper so far as the saving of fuel is derived from read before the Manchester Philosophical the burning of the smoke, it is not to effect Society, in October, 1801, and applied by that purpose alone that the fan or blower is him to the explanation of various atmosphe required - the latter has a much more im. rical phenomena, as well known.

portant duty to perform than that of merely The principal feature of Mr. -'s plan forcing the smoke through the fire, and that is the compelling all or most of the carbu. is, the blowing of the fire. The effect of a retted hydrogen, and other combustible gases, strong draught generally, is not to burn the which escape intlammation when first gene smoke, as usually understood, but rather to rated from the coal in the furnace, to return create such an intense heat, that a more again and pass through the fire, where they complete combustion of the fuel is effected, are converted into fame under the boiler. and consequently, less smoke is produced. The process is effected by placing a small Leaving out of view, for the present, the rotary fan in connexion with that part of much disputed point, as to the absolute the flue through which the smoke is passing amount of heat that it is possible to save by off to the chimney after having left the boiler. burning the whole of the smoke in any case The fan being made to revolve with consider (although all who have seen Mr. 's plan able velocity, exhausts the smoke from the in operation, at his own works, are comsmoke flue, and at the same time propels it pelled to acknowledge that it entirely burns through an additional return flue, leading to the whole of the smoke-therefore, that an enclosed ash-pit, from whence it is, by saving is effected, whatever its amount may the joint exhausting and propelling action be); it may be stated, that, in regard to reof the fan, forced to pass through the fire turning the smoke to the ash-pit, which is grate, where complete combustion is effect an essential point in this invention, it does ed, and the products of this second combus not appear that the use of the fan is absolutely tion again pass under and around the boiler indispensable; for the lighter gases, which as before, and hence up the chimney, in the constitute the most valuable part of the state of vapour, carbonic acid gas,

and azote,

smoke, have, according to Dr. Dalton's law which are perfectly colourless.

of the “ Diffusion of the Gases," before reYour chemical readers will be well aware, ferred to, a natural tendency to leave the that this circulatory process, which, for want carbonic acid gas, and rush into the ash-pit of a better word, I call double combustion as they would into a vacuum, at the same of the fuel, cannot go on without a continual time, from their buoyancy, carrying the supply of atmospheric air, which is admitted light carbonaceous matters with them ; but at a small aperture, situated between the fan the atmospheric air, which is essential to and the place where the latter communicates supply oxygen to support the combustion of with the smoke flue; and it is in the parti those gases, not having this diffusive tencular adaptation of this aperture, with re dency to so great an extent, requires to be spect to the fan and to the chimney, that the supplied by artificial means, and for that peculiar philosophical principle which dis purpose a very small fan is necessary. The tinguishes this invention is brought to bear whole of the atmospheric air that is found with so much effect.

sufficient to supply oxygen to the furnace of It was demonstrated by Dr. Dalton, in a twenty-seven-horse boiler is admitted to the paper before referred to, that different the fan through an aperture of only 10 inches gases act as vacua to each other, and it has by 4, and certainly does not require more recently been shown by Professor Graham, than a quarter of a horse power to propel it ; that the different gases have a tendency to because the smoke which passes through at

-'s pro

MALLET'S PROCESSES FOR THE PROTECTION OF IRON, ETC.

39 the same time, both from its levity and the thus effected, produces what is, I believe, mestural tendency to diffusion, before men called by some mineralogists, and others tionel, rather assists the propulsion of the conversant with the use of the blowpipe, the fan than otherwise. By running the fan at deoxidising flame.” At any rate, a simi1 sufficient speed, of course any degree of lar result is characteristic of Mr. draught can be obtained that may be thought cess, in contradistinction to the ordinary Becessary, even to the burning of the anthra process of blowing the fire with crude air; cite, or stone coal, or any common coal of which latter method, whenever resorted to, inferior quality. Indeed, a considerable speed has always effected the rapid oxidation of the is necessary; for, as Sir Humphrey Davy grate bars, and the destruction of the furnace; loog ago proved (and on which the theory of but, according to Mr. -—'s plan, where his safety lamp is founded), carburetted hy. the smoke itself is actually made in part the drogen, or coal gas, is the least combustible medium for blowing the fire, the draught of any of the inflammable gases, and conse produces a totally different result; while the quently requires a strong draught to effect manner of effecting it is as complete and its complete combustion. And here the simple as it is unique in its application to question will no doubt occur to many, as to steam-engine furnaces. what is the probable effect of this necessarily In conclusion, allow me to observe, that, strong draught, or “blast," against the in the above attempt to illustrate what I conboiler bottom. This is an important ques ceive to be one of the greatest discoveries of tion ; but it fortunately admits of being modern times, I am in no way anxious to be easily answered by any chemist who duly considered as giving the only true explanaconsiders the rationale of the process, as tion of the scientific principles concerned given above; and the practical man, who in it. My intention has been principally to will take nothing but facts, will find, upon state facts for the consideration of the more inspection, that boilers have been working experienced chemist; and if, in attempting sonde months on this plan, with fires con to theorise upon the subject, I have overstantly under them, apparently capable of stepped the legitimate province of the pracgiving a welding heat to iron, without sus tical experimentalist, I have to plead, that I taining the slightest injury; and, moreover, have been urgently requested so to do by he will find, that the underside of the grate several manufacturers, whose interests are bars, upon which such intense combustion likely to be most extensively affected by the has been going on, is never found at a higher invention; and I may add, that the subject temperature than the metal of the burner of is not the less interesting, as it affects the an ordinary gas light.

health and comfort of the population of all The ash-pit is, under the circumstances, large towns. conserted into a reservoir of mixed com

R. ARMSTRONG, C.E., Manchester. bustible gases and common air, in such pro. portions as enables the latter to yield sufficient oxygen for combining with the former in the production of carbonic acid and water

MR. MALLET'S

PROCESSES (or rather steam), and thereby eliciting the

PROTECTION OF IRON FROM maximum quantity of heat from a given quantity of fuel, besides sufficient oxygen to

TION AND CORROSION, AND FOR THE

PREVENTION support the less perfect combustion of the

THE FOULING raw coal, when first thrown upon the firegrate. Moreover, as these changes and com The discovery of an effectual means of binations are being continually and rapidly protecting iron, copper, and other meeffected, and although they are only the well tallic surfaces, from the injurious effects known phenomena of ordinary combustion,

of exposure to atmospheric and aqueous yet they are, in this case, carried on in an influences, had long been an object of atmosphere (so to speak) surcharged with a

earnest, but nearly unavailing pursuit, certain proportion of nitrogen and steam, which, being neither supporters nor com

as well among men of science as among bustibles, but being propelled by the fan in

mere practicians, when the successful nniform mixture with other elastic fluids application of iron to the building of that possess these properties in an eminent

ships gave suddenly a new impetus and degree, there can be no doubt that, in this great increase of importance to the inprocess of double combustion, those two in quiry. Sir Humphrey Davy had found combustible substances effect the very im out how to save copper sheathing from portant purpose of diluting and modifying corrosion, by means of zinc protectors; the oxidating property of the “blast." ' In but subsequent experience showed that, fact, the peculiar mixture of elastic fluids in proportion as the copper was thus

FOR THE

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SHIPS.

electro-chemically preserved, it was ren series of remedial processes with so much dered more liable to be fouled by the of science, and therefore of sufficient adhesion of animal and vegetable sub reason in them, as to leave no doubt on stances—an evil scarcely inferior in mag our minds of their perfect efficiency. To nitude to that of the destruction of the indicate briefly Mr. Mallet's discoveries, copper itself; and farther than the point they may be said to consist, first, in a so reached by Davy, science had not ad method of zincing iron so perfectly, that vanced, when the first iron ship was not a spot of the iron is, or can be, left launched into the deep. Much was at unprotected ; second, in a method of one time said of certain patented pro protecting iron and other metals by cesses of zincing, by which it was alleged means of palladium, (at a moderate iron could be so thoroughly coated, as cost.) which renders them as incor. not to leave a speck unexposed for air or rodible by air and moisture as palladium water to act upon—and much was hoped itself (palladiumizing, it may be called, from them; but one after another they with as much propriety as we say, zincall proved decided failures. In the best ing, or gilding, or soldering ;) and, zinced sheets of iron produced by these third, in a new paint, to which, from its processes, there were always found a life-destroying properties, Mr. Mallet number of spots which had been left has given the name of zoofagous paint, bare, by the collection of rust on which, by the application of which to vessels, the protective power of the zinc, in re whether of wood or iron, or with whatspect to the remainder of the iron, was ever material they may be sheathed, almost entirely neutralized. Of “anti- fouling is rendered impossible. The corrosive” and “anti-barnacle" paints following details of these processes, which and varnishes there had been also an we have great pleasure in being the first abundance, both before and since the to lay before the public, we extract from days of Davy, but not one which could Mr. Mallet's specification, which has be said to have survived the test of prac been just enrolled. * tice, or which was not, more or less, of

1. The Zincing Process. an empirical character. So matters stood—that is to

Supposing the articles about to be zinced, about

say, the time of iron first coming into ex.

are plates and ribs of iron, intended to be

employed in the construction of an iron ves. tensive use for the construction of ships

sel, they are first carefully cleaned from all --when the British Association were in

adhering oxide. With this view they are duced to take up the question, as one of immersed edgewise in a suitable vessel of the most practically important of the day, wood, pottery, stone or lead, containing dilute and to devote a portion of their funds to sulphuric acid of the specific gravity of about the institution of a series of experiments 1•300 at 60° of temperature, or dilute in relation to it, under the direction of hydrochloric acid of the specific gravity of Mr. Robert Mallet, of Dublin, a gentle about 1.060 at 60° of temperature, formed man eminently fitted, by practical habits by diluting these acids respectively as they and experience, as well as by scientific are usually found in commerce with rather knowledge, to do justice to the task in

more than an equal bulk of water, As it is trusted to him. The details and results of importance that the scales of oxide should of these experiments are related in two

be detached as rapidly as possible, the diluted

acid should be warmed; and this may be con. reports made by Mr. Mallet to the As.

veniently effected by means of a steam jacket sociation, and published in their Trans

round the vessel, or by blowing steam into actions : and though they go little farther

the acid; the acid vessel, or “ Cleansing than to show the defects of existing pro Bath,” as it may be termed, should be so cesses, (that of zincing more particu constructed for operations on a great scale, larly,) they must be allowed to have ac

that the lower portion of the acid, and the complished a most valuable service, in scales which are precipitated, can be occahaving cleared the subject from the vast sionally withdrawn to prevent waste of acid, mass of false science and erroneous prac. or the cleansing process from being incontice by which it had become encumbered. veniently protracted. The iron must be Mr. Mallet, following out the course

wholly, not partially immersed, and the of investigation thus auspiciously com.

bubbles of gas formed on its surface must be menced, has since happily mastered all

free to ascend in the fluid and escape. As the difficulties of the case, and devised a Enrolment Ofice, January 7, 1842,

MALLET'S PROCESSES FOR THE PROTECTION OF IRON, ETC. 41 soon as the scales of oxide have become de

proportion of a pound or thereabouts of po. tached or loosened, the articles are to be tassium or sodium to every ton weight of the removed from the “cleansing bath," thrown alloy of zinc and mercury, or in some cases into or washed with cold water, and struck less will suffice ; either potassium or soor hammered to shake off and detach the dium will answer the purpose, but Mr. Malscales. In the case of flat boiler plates they let prefers the latter, as more easily obtained may be advantageously passed backwards and more manageable. Whether it is poand forwards, through the machine known tassium or sodium which is used, it is removed to boiler makers as “a mangle.” The sur from the naphtha, or other fluid in which faces of the iron are then to be thoroughly it is customary to keep these metals, in scoured, by hand or by any suitable ma order to preserve them from oxidation, in chinery, with sand or emery, or with pieces of small portions of not more than half an grit stone, while exposed to a small running ounce at a time, and by means of a small stream of water, until they appear quite clean inverted cup of wood, formed on the end of and of a bright metallic lustre. The articles a stick, thrust rapidly below the surface of are now, before being allowed to dry, to be the alloy of zinc and mercury, so as to avoid plunged into a "preparing bath,” consisting any waste or combustion of the alkaline of the following mixture : A saturated cold metal. A triple alloy is thus formed of zinc, solution of chloride of zinc is made by dis mercury, and sodium or potassium, which, solving zinc or its oxide in hydrochloric acid ; having been again stirred and mixed with the to this is added an equal bulk of a saturated rod of dry wood, or of iron coated with clay, cold solution of sal ammoniac; and to the is now ready for covering or coating the mixed solutions as much more sal ammoniac prepared iron. The combination of these in the solid state is added, as they will dis. metals is facilitated, and their oxidation on solve. Or, these solutions may be made and the surface retarded, by pouring upon their mixed hot, and the solid sal ammoniac then fluid surface some of the liquor of the preadded, but the addition of some cold water will paring bath, or strewing upon it some of the then be requisite to dissolve the whole of salts dissolved in that liquor in a dry state. the salts so formed. The bath may also be The plates or ribs of iron are now to be formed of sulphate of zinc and sulphate of taken up out of the preparing bath, perammonia, or acetate of zinc and acetate of mitted to drain for a few seconds, and while ammonia, or of any other soluble salt of zinc still wet with the liquor of the preparing and ammonia or salt of manganese and ammo bath, immersed in the triple alloy in a state nia. The nitrates of zinc and ammonia are of fusion. As soon as they have acquired the least advantageous, and it is stated that the temperature of the bath of alloy, they none answer the purpose so well as the chlo. are to be withdrawn from the metallic bath ride of zinc and sal ammoniac first before edgewise or endwise, when they will be found directed to be used. No free acid should be covered with a perfectly uniform and cohepresent in these solutions. As soon as the rent coat or surface of the alloy. The affisurfaces of the immersed articles appear nity of this alloy for iron is, however, so covered all over with minute bubbles of gas intense, and the peculiar circumstances of they are then in a fit state for combining surface as induced upon the iron presented with the metallic alloy with which they are to it by the preparing bath are such, that next directed to be coated; but they may be care is requisite lest by too long an immerallowed to remain in the preparing bath for sion the plates are not partially or wholly any convenient length of time without injury dissolved. Indeed where the articles to be or prejudice to the subsequent processes. The covered are small, or their parts minute, metallic alloy last referred to is prepared in such as wire or nails or small chain, it is the following manner : A quantity of zinc is necessary before immersing them to permit melted in a suitable vessel (one formed of the triple alloy to dissolve or combine with pottery or stone is found to answer best), and some wrought iron, in order that its affinity when it is in a state of fusion, mercury or for iron may be partially satisfied and thus quicksilver is added, in the proportion of 202 diminished. At the proper fusing temperaparts of mercury to 1292 parts of zinc (both ture of this alloy, which is about 680° Fahr. by weight) being in the proportion of one it will dissolve a plate of wrought iron of an atom of mercury to forty atoms of zinc, both eighth of an inch thick in a few seconds. No upon the hydrogen scale. The two metals sputtering is produced by the immersion of are well stirred or mixed together with a rod the iron wet from the preparing bath into of dry wood or of iron coated with clay; and the alloy; but care is to be taken that there when this has been done there is added one are no hollow places or cavities in the articles or the other of the metals known to che. immersed which the alloy cannot wholly fill; mists and others as potassium and sodium lest in such case steam may be generated (the metallic bases, of which the well known below the surface of the metal, and a dangeralkalics potash and soda, are oxides) in the ous explosion be thereby occasioned. It is

more.

stated to be desirable that the melting vessels boil it in an iron vessel, for three or four should be as deep and expose as small a sur hours; add gradually 16 lbs. of red lead and face as the nature of the articles to be im litharge ground together to a fine powder in mersed will allow. At the moment of immer equal proportions,

with 10 imperial gallons sion of the articles, the surface of the alloy is of drying linseed oil, and bring all nearly to to be cleansed of all dross or oxide by a a boiling temperature. Melt in a separate wooden skimmer. As soon as the iron plates vessel 8 lbs. of gum anime (which need not or ribs are withdrawn from the alloy or be of the clearest or best quality); add to it “ Metallic Bath,” they are to be plunged two imperial gallons of drying linseed oil, into cold water and well washed therein. boiling, and 12 lbs. of caoutchouc softened, The surface of the iron is now in a condition or partially dissolved by coal tar naphtha permanently to resist corrosion and oxidation (as practised by the makers of water-proof in air, or in salt or fresh water.

cloths). Mix the whole together in the All the foregoing operations are best per former vessel, and boil gently until, on taking formed upon the plates or ribs after they some of the varnish between two spatulas, it have been bent and fitted to their places, and is found tough and ropy. When this “ body" the plates have been riveted together into is quite cold it may be thinned down, with large pieces of eight to ten feet square or from 30 to 35 gallons imperial of turpentine,

When again put “into frame," or or of coal naphtha, which will make it ready for placed in their respective positions in the use. Mr. Mallet states this to be the best var. ship’s hull, they are directed to be united by nish he is acquainted with for this purpose. It rivets countersunk from the outside, and is not acted on when dry and hard, by any moconsequently headed inside the vessel. The derately diluted acid or caustic alkali; it does countersunk heads of these rivets are to be not by long immersion combine with water, also coated with the triple alloy in the man and so form a white, and partially soluble ner before described, and tongs of iron are hydrate, as all merely resinous varnishes and to be provided, having a very large mass all oil paints do ; it is, moreover, so elastic, of metal in their jaws, between which a hol. that a plate covered with it may be bent for low seat, of the shape and size of the coun several times without its peeling off. And, tersunk rivet head, is to be formed to receive it. lastly, it adheres so fast, that nothing but a An alloyed rivet being seized by a pair of sharp edged instrument will scratch it off the such tongs may have its point heated to a surface of iron. The composition No. 2 is riveting or welding heat without injuring the of a cheaper sort, but not quite so good. coat of alloy upon its countersunk head; for Common coal or gas tar is to be boiled in the heat is carried off from the latter so fast an iron cauldron, at so high a temperature, by the contact of the large mass of iron in that the smoke from it is of a yellow dun the jaws of the tongs, which are to be cooled colour ; or the tar is to be caused to flow occasionally, as to prevent the head of the through red-hot iron tubes.

The boiling rivet becoming hot during the heating of the passage through the tubes is to be continued point in a common smith's fire.

until the residue is a solid asphaltum, break. The hull of the iron vessel, being thus ing with a pitchy fracture. It is essential completed, and wholly covered with the that the boiling should be carried on at this alloy, is then to receive a coat of varnish all high temperature, as the permanence of the over, of either of the compositions about to varnish in water depends upon the tar having be described. If possible, this varnish should been submitted to the temperature at which be laid on with a spatula or thin flexible naphthaline is formed, by the decomposition blade of horn, or some such material, as a or breaking up of the original constitution of brush produces minute air bubbles, which the tar. Take 56 lbs. of this coal tar asleaves spaces uncovered on the drying of phaltum ; melt it in an iron vessel: add 10 the varnish. The varnish will dry, or get imperial gallons of drying linseed oil, ground hard and coherent, at ordinary temperatures ;

with 25 lbs. of red lead and litharge, in equal but when practicable, it is desirable to expose proportions ; add to the whole, when well it for some hours to a temperature of about mixed, and after boiling together for two or 300° Fahrenheit, which gives it greater ad three hours, 15 lbs. of caoutchouc, softened hesion and durability. The iron surfaces or partially dissolved by coal naphtha, as may be warmed in successive portions by before described ; and when cold, mix with heat radiated from “ chauffers" or open

20 to 30 gallons of turpentine, or coal fires of coke, or by any other convenient naphtha, which will make the varnish ready The varnish may be either of a

for use, composition, which Mr. Mallet terms No. 1, 2. The Palladiumizing Process. or of another, which he terms No. 2. The The articles to be protected are to be first composition, No. 1, is formed as follows : cleansed in the same way as in the case of Take 50 lbs. of foreign asphaltum, melt and zincing, namely, by means of the double

means.

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