1841.] 



THE CnaL ENGINEER AND ARCHITECTS JOURNAL. 



.353 



THE ZINKING PROCESS. 



We derive from the Revue Generate de VArcMltcture llie materials 

 for the following notes on the process of zinking iron, us described by 

 the Baron Menu de Mesnil, in the Report of the Committee of Inquiry 

 to the Minister of Marine in France. On the importance of preserv- 

 ing iron from oxydation it is unnecessary to make any remark, we 

 may just observe that the only effective modes hitherto used have been 

 tinning and glazing. In 1742 M. Maloin presented to the Royal Aca- 

 demy of Sciences a memoir on the analogy which he had observed be- 

 tween iron and tin, and points out a mode of zinking iron similar to the 

 modern one. Whether the price of zinc was then too high or other 

 difficulties stood in the way, it was not until 183G, that tlie process of 

 zinking was made effective by M. Sorel, wlio took out a patent for it 

 under the name of Galvanization of Iron. On the iSth September 

 1838, a committee was named by tlie Minister of Marine to make ex- 

 periments in the dockyard at Brest on zinking iron, by them a first 

 report was made recommending experiments to be made on a larger 

 scale, which latter commenced on the 14(h of May ISIO, and it was on 

 the 30th April of the present year that they made their report. 



The process consists simply in dipping an iron article, previously 

 cleaned with acid, for 3 or 4 minutes into zinc infusion, then taking it 

 out progressively, shaking it in the air to get rid of the excess of zinc, 

 and at last plunging it suddenly in cold water; after which it only re- 

 quires to be rubbed over with fine sand and dried. What is called 

 Galvanization is therefore nothing more than a process similar to 

 tinning; but while iron is rendered more oxydable by contact with 

 tin, and oxidizes rapidly, if by any mistake in the preparation the iron 

 is left uncovered in any point ; in zinking, on the contrary, a true alloy 

 of zinc is formed on the surface of the iron, and the parts accidentally 

 left unzinked alone rust, and the evil is soon stopped. This latter fact 

 is enough to prove that the iron is not protected by any Galvanic effect 

 as is the opinion generally received. Thus in the operations pre- 

 paratory to zinking, such as cleaning by acid, &c., great care is taken 

 to free the surface of the iron by scraping from it all matters which 

 would resist the action of the acid, and prevent zinc from attaching to 

 the iron all over. 



The cleaning with acid is an operation which requires much care, 

 for while it is indispensable that the iron subjected to the acid should 

 be wholly free from rust, care must also be had that the iron be not 

 too strongly acted upon by the acid, but be taken out at the proper 

 moment. Very weak acids only are used for the cleaning as a mix- 

 ture of nine parts of sulphuric acid with 100 of water. In France the 

 refuse acid used in purifying vegetable oils is also employed ; after a 

 certain time the acid can no longer be used, as it is almost wholly 

 turned into sulphate of iron, a salt which may be readily extracted, 

 and which would bring more than the worth of the acid used. The 

 time during which the iron is kept in the acid varies according to the 

 degree of rust from 12 to 24 hours. 



The pieces after coming out of the acid bath are cleaned and passed 

 rapidly into hydrochloric acid of 15^, and then put in a stove to be 

 quite dried. It is in this state of absolute dryness that they may be 

 plunged into the zinc infusion. At the time of immersion the object 

 is powdered over with sal-ammoniac, a great part of which volatilizes, 

 and then decomposes, and the remainder, the acting portion, cleanses 

 the object a third time, and makes the zinking certain and perfect. 

 The use of this salt, on account of its value and the large quantity 

 used, forms a great part of the cost of zinking. The zinc bath soon 

 becomes covered with a black fluid matter, without adherence to the 

 surface of the bath, on which it forms a continuous layer. The work- 

 men consider it as advantageous to the zinking, and therefore take it 

 out of the bath after the day's work, and put it in again the next 

 morning, when they go back to work. During the night the zinc it 

 kept in fusion, and the surface exposed to the air, is tarnished and 

 oxydized, and it may be therefore allowed that the black matter acts 

 so as to dissolve the oxide formed, and thus to restore the surface of 

 the zinc to the purity requisite for zincing properly. An analysis of 

 this black matter, made at Brest by M. LangonneJ First Class Naval 

 Apothecary and Member of the Committee, shows it to be composed 

 of a great quantity of chlorure of zinc, a small portion of chlorure of 

 iron, and an insoluble compound of ammoniac and zinc. As we know 

 therefore that chlorure of zinc and ammoniac are good detersives, it is 

 not surprising that the black matter, having an analogous composition, 

 should be equally efficacious. The time that objects remain in the 

 zinc bath depends on the dimension, if they are thin, they must be 

 only rapidly passed through, if massive they must be left some minutes. 

 In general it is enough to take the objects out as soon as they leave 

 off giving out smoke or rather steam. 



The immersion of the zinked object, still quite hot, in cold water. 



is for the purpose of preventing the formation of oxide of zinc, which 

 tarnishes the surface, but this operation gives the iron a kind of tem- 

 pering, which added to the effect of a layer of alloy covering the sur- 

 face, renders it more brittle. Sheet iron in particular, on account of 

 its thinness, is subject to this inconvenience, and can no longer be bent 

 with ease. An improvement has however been recently made, which 

 avoids the dipping, the slight layer of oxide of zinc which is formed 

 on the surface, and which does not stick, is easily got rid off by rubbing 

 after the object has been cooled in sawdust and sand. 



When objects have just been zinked, they have a metallic lustre, 

 which they will keep for a long time, when free from damp, but when 

 left in the air they by little and little tarnish, become covered with a 

 whitish efflorescence, which increases, acquires consistency, sticks to 

 the metal, and soon forms a continuous and solid layer, which preserves 

 the surface from ulterior alteration. This transformation is slow in 

 taking effect, and appears to be complete only after 15 or IS months' 

 exposure to the air. Even the weakest acids and the alkalis attack 

 and dissolve the zinc with the greatest facility and bare the iron. 

 Heated red for several minutes the layer of zinc in excess soon peels 

 off, but the iron is not yet bared, as the alloy of zinc and iron, more 

 adiierent, harder, and less fusible, long repel the action of heat. 



The thickness of the zinc layer is very small; on cannon balls it 

 was only IG hundredths of a millimeter, on sheet iron it was from 7 

 to 12 thousandths of a millimeter, 9 thousandths is the mean. The 

 thickness has little ert'ect on the windage of cannon balls, but the com- 

 mittee suggest that zinking might be employed to increase the dia- 

 meter of deficient balls. The committee farther suggest that experi- 

 ments should be made to zinc old iron objects in order to preserve 

 them. The thickness of the layer of zinc, although so very small, is 

 amply sufficient, when we consider that an alloy is formed with the 

 iron, which extends its protective influence deeper into the met;d._ 



The influence of the air or water is very little on the zinked iron, 

 if entirely exposed, but if subjected to the action of water and air al- 

 ternately', they are more affected. Zinked apparatus produces no 

 injurious effect upon drinkable water. 



As to the various articles on which they experimented the com- 

 mittee report that the zinking appears very effective for roofs and 

 cisterns. Zinked nails and bolts are recommended for shipping, but 

 the committee are not yet prepared to recommend them to supersede 

 copper. These nails are recommended for the decks of ships, as the 

 ordinary nails soon produce a black spot on the surface of the wood, 

 which penetrates and affects the fibres, gallate of iron being produced. 

 Zinked nails are strongly urged as substitutes for iron in securing 

 slates on root's, as the iron nails soon rust, particularly near the sea, 

 and in high winds are the chief cause of the slates falling. The zinked. 

 gutters the Committee consider will supersede tin. For the flues of 

 stoves the zinked iron is recommended, and zinked wire also meets 

 with their approbation. They had not made suflicient experiments 

 as to chains, but they reported that those which they had tried, when 

 put to the hydraulic test, supported it well. For locks and bolts in 

 lighthouses and sea buildings, zinking is exclusively advocated. An 

 advantage which zinc possesses for ear-rings for sails is that it does 

 not rust the sails, which is apt to rot them. 



The Committee conclude by making several recommendations. They 

 report that zinking of wrought and cast iron can easily be practised in 

 all ordinary circumstances of the use of that metal, that zinking shows 

 every symptom of durability, and that it is of the greatest advantage 

 to the navy. They consequently recommend a contract to be made 

 with the patentee for the use of zinc in the arsenals of France, being 

 convinced of its efficacy. 



S. L. AND CANDIDUS. 



The question at issue between S. L. and myself seems as it were 

 about to be protracted as interminably as a Chancery suit. However 

 we now seem to understand each other somewhat more clearly than at 

 first : — at least there is one point on which he expresses himself de- 

 cidedly, and on which I can cordially agree with him ; since so far 

 from attempting to defend, he unscrupulously reprobates that sickly 

 soidisant Greektsm, and pseudo-classical style, which during the last 

 thirty years have given us so many " insipid abortions," where oppor- 

 tunities—now, alas ! not to be recovered — presented themselves for 

 achieving noble and original works. 



Most certainly S. L. is not mistaken, when he imagines I will admit 

 that Grecian and Roman architecture affords resources not yet worked 

 out, ideas so capable of being yet further extended, that they may be 

 said to be as yet only very partially developed, whereas they have 



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