40 MALLET'S PROCESSES FOR THE PROTECTION OF IRON, ETC. electro-chemically preserved, it was rendered more liable to be fouled by the adhesion of animal and vegetable substances an evil scarcely inferior in magnitude to that of the destruction of the copper itself; and farther than the point so reached by Davy, science had not advanced, when the first iron ship was launched into the deep. Much was at one time said of certain patented processes of zincing, by which it was alleged iron could be so thoroughly coated, as not to leave a speck unexposed for air or water to act upon-and much was hoped from them; but one after another they all proved decided failures. In the best zinced sheets of iron produced by these processes, there were always found a number of spots which had been left bare, by the collection of rust on which, the protective power of the zinc, in respect to the remainder of the iron, was almost entirely neutralized. Of "anticorrosive and "anti-barnacle" paints and varnishes there had been also an abundance, both before and since the days of Davy, but not one which could be said to have survived the test of practice, or which was not, more or less, of an empirical character. So matters stood-that is to say, about the time of iron first coming into extensive use for the construction of ships -when the British Association were induced to take up the question, as one of the most practically important of the day, and to devote a portion of their funds to the institution of a series of experiments in relation to it, under the direction of Mr. Robert Mallet, of Dublin, a gentleman eminently fitted, by practical habits and experience, as well as by scientific knowledge, to do justice to the task intrusted to him. The details and results of these experiments are related in two reports made by Mr. Mallet to the Association, and published in their Transactions and though they go little farther than to show the defects of existing processes, (that of zincing more particularly,) they must be allowed to have accomplished a most valuable service, in having cleared the subject from the vast mass of false science and erroneous practice by which it had become encumbered. Mr. Mallet, following out the course of investigation thus auspiciously commenced, has since happily mastered all the difficulties of the case, and devised a series of remedial processes with so much of science, and therefore of sufficient reason in them, as to leave no doubt on our minds of their perfect efficiency. To indicate briefly Mr. Mallet's discoveries, they may be said to consist, first, in a method of zincing iron so perfectly, that not a spot of the iron is, or can be, left unprotected; second, in a method of protecting iron and other metals by means of palladium, (at a moderate cost,) which renders them as incorrodible by air and moisture as palladium itself (palladiumizing, it may be called, with as much propriety as we say, zincing, or gilding, or soldering ;) and, third, in a new paint, to which, from its life-destroying properties, Mr. Mallet has given the name of zoofagous paint, by the application of which to vessels, whether of wood or iron, or with whatever material they may be sheathed, fouling is rendered impossible. The following details of these processes, which we have great pleasure in being the first to lay before the public, we extract from Mr. Mallet's specification, which has been just enrolled.* 1. The Zincing Process. Supposing the articles about to be zinced, are plates and ribs of iron, intended to be employed in the construction of an iron vessel, they are first carefully cleaned from all adhering oxide. With this view they are immersed edgewise in a suitable vessel of wood, pottery, stone or lead, containing dilute sulphuric acid of the specific gravity of about 1.300 at 60° of temperature, or dilute hydrochloric acid of the specific gravity of about 1060 at 60° of temperature, formed by diluting these acids respectively as they are usually found in commerce with rather more than an equal bulk of water. As it is of importance that the scales of oxide should be detached as rapidly as possible, the diluted acid should be warmed; and this may be conveniently effected by means of a steam jacket round the vessel, or by blowing steam into the acid; the acid vessel, or Cleansing Bath," as it may be termed, should be so constructed for operations on a great scale, that the lower portion of the acid, and the scales which are precipitated, can be occasionally withdrawn to prevent waste of acid, or the cleansing process from being inconveniently protracted. The iron must be wholly, not partially immersed, and the bubbles of gas formed on its surface must be free to ascend in the fluid and escape. As 66 • Enrolment Office, January 7, 1842, MALLET'S PROCESSES FOR THE PROTECTION OF IRON, ETC. soon as the scales of oxide have become detached or loosened, the articles are to be removed from the "cleansing bath," thrown into or washed with cold water, and struck or hammered to shake off and detach the scales. In the case of flat boiler plates they may be advantageously passed backwards and forwards, through the machine known to boiler makers as "a mangle." The surfaces of the iron are then to be thoroughly scoured, by hand or by any suitable machinery, with sand or emery, or with pieces of grit stone, while exposed to a small running stream of water, until they appear quite clean and of a bright metallic lustre. The articles are now, before being allowed to dry, to be plunged into a "preparing bath," consisting of the following mixture: A saturated cold solution of chloride of zinc is made by dissolving zinc or its oxide in hydrochloric acid; to this is added an equal bulk of a saturated cold solution of sal ammoniac; and to the mixed solutions as much more sal ammoniac in the solid state is added, as they will dissolve. Or, these solutions may be made and mixed hot, and the solid sal ammoniac then added, but the addition of some cold water will then be requisite to dissolve the whole of the salts so formed. The bath may also be formed of sulphate of zinc and sulphate of ammonia, or acetate of zinc and acetate of ammonia, or of any other soluble salt of zinc and ammonia or salt of manganese and ammonia. The nitrates of zinc and ammonia are the least advantageous, and it is stated that none answer the purpose so well as the chloride of zinc and sal ammoniac first before directed to be used. No free acid should be present in these solutions. As soon as the surfaces of the immersed articles appear covered all over with minute bubbles of gas they are then in a fit state for combining with the metallic alloy with which they are next directed to be coated; but they may be allowed to remain in the preparing bath for any convenient length of time without injury or prejudice to the subsequent processes. The metallic alloy last referred to is prepared in the following manner: A quantity of zinc is melted in a suitable vessel (one formed of pottery or stone is found to answer best), and when it is in a state of fusion, mercury or quicksilver is added, in the proportion of 202 parts of mercury to 1292 parts of zinc (both by weight) being in the proportion of one atom of mercury to forty atoms of zinc, both upon the hydrogen scale. The two metals are well stirred or mixed together with a rod of dry wood or of iron coated with clay; and when this has been done there is added one or the other of the metals known to chemists and others as potassium and sodium (the metallic bases, of which the well known alkalies potash and soda, are oxides) in the 41 proportion of a pound or thereabouts of potassium or sodium to every ton weight of the alloy of zinc and mercury, or in some cases less will suffice; either potassium or sodium will answer the purpose, but Mr. Mallet prefers the latter, as more easily obtained and more manageable. Whether it is potassium or sodium which is used, it is removed from the naphtha, or other fluid in which it is customary to keep these metals, in order to preserve them from oxidation, in small portions of not more than half an ounce at a time, and by means of a small inverted cup of wood, formed on the end of a stick, thrust rapidly below the surface of the alloy of zinc and mercury, so as to avoid any waste or combustion of the alkaline metal. A triple alloy is thus formed of zinc, mercury, and sodium or potassium, which, having been again stirred and mixed with the rod of dry wood, or of iron coated with clay, is now ready for covering or coating the prepared iron. The combination of these metals is facilitated, and their oxidation on the surface retarded, by pouring upon their fluid surface some of the liquor of the preparing bath, or strewing upon it some of the salts dissolved in that liquor in a dry state. The plates or ribs of iron are now to be taken up out of the preparing bath, permitted to drain for a few seconds, and while still wet with the liquor of the preparing bath, immersed in the triple alloy in a state of fusion. As soon as they have acquired the temperature of the bath of alloy, they are to be withdrawn from the metallic bath edgewise or endwise, when they will be found covered with a perfectly uniform and coherent coat or surface of the alloy. The affinity of this alloy for iron is, however, so intense, and the peculiar circumstances of surface as induced upon the iron presented to it by the preparing bath are such, that care is requisite lest by too long an immersion the plates are not partially or wholly dissolved. Indeed where the articles to be covered are small, or their parts minute, such as wire or nails or small chain, it is necessary before immersing them to permit the triple alloy to dissolve or combine with some wrought iron, in order that its affinity for iron may be partially satisfied and thus diminished. At the proper fusing temperature of this alloy, which is about 680° Fahr. it will dissolve a plate of wrought iron of an eighth of an inch thick in a few seconds. No sputtering is produced by the immersion of the iron wet from the preparing bath into the alloy; but care is to be taken that there are no hollow places or cavities in the articles immersed which the alloy cannot wholly fill; lest in such case steam may be generated below the surface of the metal, and a danger. ous explosion be thereby occasioned. It is 42 MALLET'S PROCESSES FOR THE PROTECTION OF IRON, ETC. stated to be desirable that the melting vessels should be as deep and expose as small a surface as the nature of the articles to be immersed will allow. At the moment of immersion of the articles, the surface of the alloy is to be cleansed of all dross or oxide by a wooden skimmer. As soon as the iron plates or ribs are withdrawn from the alloy or "Metallic Bath," they are to be plunged into cold water and well washed therein. The surface of the iron is now in a condition permanently to resist corrosion and oxidation in air, or in salt or fresh water. All the foregoing operations are best performed upon the plates or ribs after they have been bent and fitted to their places, and the plates have been riveted together into large pieces of eight to ten feet square or more. When again put "into frame," or placed in their respective positions in the ship's hull, they are directed to be united by rivets countersunk from the outside, and consequently headed inside the vessel. The countersunk heads of these rivets are to be also coated with the triple alloy in the manner before described, and tongs of iron are to be provided, having a very large mass of metal in their jaws, between which a hollow seat, of the shape and size of the countersunk rivet head, is to be formed to receive it. An alloyed rivet being seized by a pair of such tongs may have its point heated to a riveting or welding heat without injuring the coat of alloy upon its countersunk head; for the heat is carried off from the latter so fast by the contact of the large mass of iron in the jaws of the tongs, which are to be cooled occasionally, as to prevent the head of the rivet becoming hot during the heating of the point in a common smith's fire. The hull of the iron vessel, being thus completed, and wholly covered with the alloy, is then to receive a coat of varnish all over, of either of the compositions about to be described. If possible, this varnish should be laid on with a spatula or thin flexible blade of horn, or some such material, as a brush produces minute air bubbles, which leaves spaces uncovered on the drying of the varnish. The varnish will dry, or get hard and coherent, at ordinary temperatures; but when practicable, it is desirable to expose it for some hours to a temperature of about 300 Fahrenheit, which gives it greater adhesion and durability. The iron surfaces may be warmed in successive portions by heat radiated from "chauffers" or open fires of coke, or by any other convenient means. The varnish may be either of a composition, which Mr. Mallet terms No. 1, or of another, which he terms No. 2. The composition, No. 1, is formed as follows:Take 50 lbs. of foreign asphaltum, melt and : boil it in an iron vessel, for three or four hours; add gradually 16 lbs. of red lead and litharge ground together to a fine powder in equal proportions, with 10 imperial gallons of drying linseed oil, and bring all nearly to a boiling temperature. Melt in a separate vessel 8 lbs. of gum anime (which need not be of the clearest or best quality); add to it two imperial gallons of drying linseed oil, boiling, and 12 lbs. of caoutchouc softened, or partially dissolved by coal tar naphtha (as practised by the makers of water-proof cloths). Mix the whole together in the former vessel, and boil gently until, on taking some of the varnish between two spatulas, it is found tough and ropy. When this " 'body" is quite cold it may be thinned down, with from 30 to 35 gallons imperial of turpentine, or of coal naphtha,which will make it ready for use. Mr. Mallet states this to be the best varnish he is acquainted with for this purpose. It is not acted on when dry and hard, by any moderately diluted acid or caustic alkali; it does not by long immersion combine with water, and so form a white, and partially soluble hydrate, as all merely resinous varnishes and all oil paints do; it is, moreover, so elastic, that a plate covered with it may be bent for several times without its peeling off. And, lastly, it adheres so fast, that nothing but a sharp edged instrument will scratch it off the surface of iron. The composition No. 2 is of a cheaper sort, but not quite so good. Common coal or gas tar is to be boiled in an iron cauldron, at so high a temperature, that the smoke from it is of a yellow dun colour; or the tar is to be caused to flow through red-hot iron tubes. The boiling passage through the tubes is to be continued until the residue is a solid asphaltum, breaking with a pitchy fracture. It is essential that the boiling should be carried on at this high temperature, as the permanence of the varnish in water depends upon the tar having been submitted to the temperature at which naphthaline is formed, by the decomposition or breaking up of the original constitution of the tar. Take 56 lbs. of this coal tar asphaltum; melt it in an iron vessel: add 10 imperial gallons of drying linseed oil, ground with 25 lbs. of red lead and litharge, in equal proportions; add to the whole, when well mixed, and after boiling together for two or three hours, 15 lbs. of caoutchouc, softened or partially dissolved by coal naphtha, as before described; and when cold, mix with 20 to 30 gallons of turpentine, or coal naphtha, which will make the varnish ready for use. 2. The Palladiumizing Process. The articles to be protected are to be first cleansed in the same way as in the case of zincing, namely, by means of the double MALLET'S PROCESSES FOR THE PROTECTION OF IRON, ETC. salts of zinc and ammonia, or of manganese and ammonia; and then to be thinly coated over with palladium, applied in the state of an amalgam with mercury. [The directions given as to this process are meagre, in comparison to those supplied for the other processes; but we are informed that the protection afforded by the palladium is as absolute as that by the zincing, and by no means so costly as to exclude it from economical use.] 3. The Zoofagous Paint. After the iron vessel has been zinced and varnished, in the manner before described, it is done all over (above the varnish, of course,) with a strong-bodied thick paint. This is composed of drying linseed-oil, red lead, and sulphate of barytes, (or white lead may be used, but not so advantageously,) and a little turpentine. To every 100 lbs. of these ingredients, when mixed, is to be added 20 lbs., or thereabouts, of oxychloride of copper, and 3 lbs. of a mixture composed of hard yellow soap melted with an equal weight of common rosin, and a little water. The colour originally sold in commerce under the name of "Brunswick green,' "" was an oxychloride of copper; but the present Brunswick green of commerce is a different thing, and will not answer. The oxychloride of copper may be obtained at a cheap rate, by various known methods, which it is unnecessary to detail. When the whole of the hull of the vessel has been done over with the paint, it must be permitted to dry and harden for three or four days, before the ship is floated out of dock. The entire series of operations are now completed; and the hull of an iron ship so treated will, Mr. Mallet assures us, "resist all corrosion from the action of air, and fresh or sea-water, and not be liable to fouling,' by the adhesion of marine animals and plants." Mr. Mallet adds, that the power of the zoofagous paint to prevent fouling' arises from the fact, that the insoluble, or difficultly soluble salts of copper, and of certain other metals, are so noxious to the life of marine or aquatic animals and plants, which generally attach themselves to ships' bottoms, that they will not adhere or grow upon a surface so treated. The paint, therefore, is only a vehicle for poisonous matter, for which purpose it is requisite that it should have sufficient adhesion to resist the ship's motion, but still should have a slight degree of solubility in water, so that the poisonous matter may be taken up by the absorbent or capillary vessels of any adhering animal or plant. This latter property is given it by the addition of the resinous soap, the proportion of which should be varied to suit the 43 climate to which a ship is going, more being used in frigid, and less in tropical climates. Mr. Mallet prefers using the oxychloride of copper, and has found it by much the most efficacious; but any insoluble or difficultly soluble salt, of copper, mercury, arsenic, or antimony, or any combination of these, whether soluble or insoluble, may be substituted for it. General Observations, Although Mr. Mallet deems it advisable that where new ships are intended to be protected by zincing, the iron should go through the whole of the processes before directed, namely, the cleansing, the coating with the triple alloy, the varnishing, and the final coating with the zoofagous paint, he remarks that they are not all equally' essential, and points out how the same effects may be produced, though attended with less favourable circumstances, by the adoption of a part only of these processes: "For, supposing the plates and ribs of iron were merely coated with the triple alloy of zinc, mercury, and potassium or sodium, without the addition of the protective varnish and zoofagous paint, it is certain that, on the exposure of this alloy to the action of air and water, the positive metal at the surface would be first acted on, and the surface become shortly covered with a very thin coat of amalgamated zinc, which is known not to be acted upon by fluid menstrua, (except under peculiar conditions, which do not exist in the case here supposed,) and does not, as I have found by experiment, gather to itself, when exposed to sea or fresh water, any of that calcareous coating which is productive of the fouling of vessels. The advantage gained by varnishing over this triple alloy coating is of a twofold nature. In the first place, it serves as a mechanical protection to the coating, and thereby to increase its durability; and, secondly, it shields the alloy from contact with the zoofagous paint, some of the ingredients of which would exert an injurious chemical action on the alloy. The office, therefore, of the triple alloy is simply to prevent corrosion and oxidation, (including, where used by itself, that of preventing the formation of calcareous adhesions ;) that of the varnish, to protect the triple alloy; and that of the zoofagous paint, to prevent fouling, by the destruction of any marine animals or aquatic plants which may seek to attach themselves to the protected surfaces." When the addition of the zoofagou s paint is not required, to prevent fouling, as in the case of articles exposed to the action 44 SPECIFICATIONS OF RECENT ENGLISH PATENTS. of the atmosphere only, Mr. Mallet states that any desirable colour may be given to the protecting varnish, by a mixture of colouring materials, but that care must be taken that these colouring materials consist of per-oxides not liable to be acted on by air or moisture. The best method to adopt, however, with such articles, is said to be, to pay the varnish all over with a coat of oilpaint. Finally, although the triple alloy is directed in the first instance, to be employed at the fusing temperature, Mr. Mallet states that, by the addition of a larger portion of mercury, articles of cast or wrought iron or steel may be coated with that alloy at a lower temperature, and even in a cold state, by means of simple contact and friction. BADCOCK'S AUTOMATON LUBRICATOR AN TICIPATED. Dear Sir,-On perusing the Mechanics' Magazine for the past month, I read, at page 446, a description of an "Automaton Lubricator," by Mr. Badcock. This Lubricator so closely resembles an instrument which was invented by me, for the purpose of readily supplying equal measures of mercury, for dividing the capacity of glass tubes into any required number of equal parts, that it only needs to be supplied, (as mine is,) with an adjusting screw to regulate the capacity of the cavity in the plug, to make it complete for its intention. You did me the honour to notice the instrument to which I have referred in the Mechanics' Magazine, dated May 1, 1841. Believe me very faithfully yours, CHARLES THORNTON COATHUPE. Wraxhall, January 5, 1842. HOOD ON HEAT, AND THE INSTITUTION OF CIVIL ENGINEERS. Sir,-Observing in your last number a paper headed "Hood on Heat," commencing with the observation, that "The Members* of the Institution of Civil Engineers have given an extensive publicity, as well as a sort of implied sanction to the contents of a paper lately read before that body," I beg permission to remind you, that every publication issued from that institution is accompanied by an announcement expressly disclaiming the implied sanction of which you speak. I quote the following from the last volume of the Transactions. "The Institution is not responsible for the opinions, statements of facts, or trains of reasoning contained in its publications; such responsibility rests entirely with the authors of the ⚫ Error of the press, for "Minutes."-En. M. M. ABSTRACTS OF SPECIFICATIONS OF ENGLISH *** Patentees wishing for more full abstracts of their Specifications than the present regulations of the Registration Offices will admit of our giving, are requested to favour us with the loan of their Specifications for that purpose. EDWARD HAMMOND BENTALL, OF HEYBRIDGE, ESSEX, IRON-FOUNDER, for certain improvements in ploughs. Petty Bag Office, December 10th, 1841. These improvements consist, firstly, in the peculiar construction and mode of adapting an adjustable lever to the frame of the plough, for the purpose of changing the inclination of the share, which is attached to the end or nose of the lever, so that the point of the share may stand at any required angle below or above the level of the sole slade or ground of the plough. Secondly, In the particular form of the shares, and modes of attaching them to such adjustable levers. Thirdly, In the mode of affixing the breast or mould board to the plough, in order that it may rise and fall with the adjustable lever and share. Fourthly, In the means of contracting or expanding the breasts of a double breast plough, when such double breast is cast or formed in one piece. The first improvement is carried out in the following manner: a lever is placed at the front of the frame, having at its lower end a groove, in which a step on the sole of the plough works, allowing a small movement backward and forward; beyond this fulcrum the lever is fixed to the ploughframe by a loose bolt. At the top of the lever, on its front face, is a screw, which passes through the centre of a projecting piece or ear of the plough-frame, being secured in any required position by a nut on each side of the ear or projection. By shifting these nuts backward or forward, therefore, the position of the lever is varied, and any required degree of inclination obtained at pleasure. Another arrangement is shown and described, differing from the former only in, |