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THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



[November, 



cast steel, after " tilting," has the average minimum corrosion, and low 

 shear steel, which is in fact a sort of steely iron, has the maximum. 



The author has made researches on the nature of the peculiar carbona- 

 ceous substance which he has called " plumbago," formed by the decompo- 

 sition of cast iron in sea water, and in other conditions, and also occasionally 

 from wrought iron and steel, and on the other organic products of such de- 

 compositions. His reasonings tend to show, that this plumbago in part re- 

 sults from the decomposition of carbonic acid in solution in the water, and 

 is therefore highly interesting to the chemist, as an instance of crystallized 

 carbon being so formed. The rust produced by the prolonged action of air 

 and water on iron, is brown haematite; and omitting all minute or accidental 

 constituents of the iron, its formula is 2 Fe 2 3 + 3 HO, more or less mixed 

 with spathic iron ore = Fe x CO 2 . When very old, these lose water, and 

 become " fer oligiste," or anhydrous peroxide. The author then discusses 

 the conditions most and least favourable to corrosion in marine steam-boilers, 

 with reference to the degree of saline concentration, boiling temperature, 

 &c, of the sea water; and gives tables of the saline contents at various 

 stages of concentration. Sea water, to act least on boilers, should be heated 

 to 190° Fahrenheit, and be deprived of air before entering as feed water, 

 and the less concentration takes place, the less will be the amount of corro- 

 sion. The tables of the amounts of corrosion of cast iron, in contact with 

 definite alloys of copper with tin and zinc, are now extended to wrought iron. 

 The corrosion of this is accelerated by the contact of either brass or gun- 

 metal in sea water, but more so by the latter than by copper. He confirms 

 his previous results that, except in atmospheric air, a coating of zinc, or 

 contact of zinc in a massive form, affords to cast or wrought iron only par- 

 tial protection from corrosion. 



In foul sea water, the zincing is converted into artificial blende = (Zn + Fe 

 + S). Elkington and Ruolz's zincing process he finds capable of many 

 useful applications for iron exposed to air, but he questions its efficacy in 

 water, or where there is abrasion. Zink paint he states to have been found 

 the most durable of all the paints and varnishes tried, except coal-tar laid 

 on hot, and the asphaltic varnishes. The author then enters largely into 

 many questions relative to the corrosion and fouling of iron ships, applying 

 to them the laws he had previously deduced. Based on the known effects 

 of a slightly alkaline solution in preventing corrosion, he proposes lime- 

 water to replace bilge-water, and thus to prevent internal corrosion in iron 

 ships. He describes his prolonged experiments on the means of preventing 

 their external corrosion and fouling, and the details of his methods of pre- 

 venting both. These consist in coating the plates with an alloy of zinc with 

 mercury, and a very minute portion of the base of cither of the alkalies. 

 The coating is effected by peculiar methods to ensure perfect uniformity; 

 and the principle of protection is, that the alloy produces by the first action 

 of a menstruum, a surface of amalgamated zinc which is insoluble. This 

 coating is protected by an asphaltic varnish, to prevent the contact of the 

 slightly soluble poisonous paint, with which the ship's hull is payed over to 

 prevent fouling. Several metallic salts are fitted to act as poisons to the 

 molluscous and testaceous animals which infest ships' bottoms ; but the 

 author's experience leads him to prefer oxychloride of copper, which is, in 

 fact, the salt formed on common copper sheathing, and which by its poi- 

 sonous qualities keeps it clean. 



The author's method has been in use for some time on vessels which have 

 made voyages to the tropics, and its usefulness in preventing fouling, Sic., 

 has been fully proved. He discusses and explains the errors which have 

 been made as to the non-corrosion of ships kept in motion, and shows that 

 corrosion docs take place, but that it is not so perceptible as when the ship 

 remains at rest. He shows that magnetism has nothing whatever to do with 

 the amount of corrosion in iron vessels, and also discusses at length, various 

 contingent circumstances promoting partial corrosion in iron ships : the 

 nature of cargo, the mode of fastening the machinery, the contact of boilers, 

 of various timbers, and of the same when decayed, &c. ; all of which are of 

 practical importance to the iron ship-builder or marine engineer. Kyanized 

 timber is rapidly destructive of iron, in contact with it ; in sea water it more 

 than doubles the rate of its corrosion. After giving a table containing the 

 numerical values, for iron ship-building, of a number of qualities of British 

 wrought iron, the author proceeds to discuss in detail the principal methods of 

 protection for iron, which have been recently promulgated by Berry, Neilson, 

 Shore, Elkington and Koulz, Hall of Bermondsey, Crawford and Fountain- 

 Moreau, all of which are patented ; but none of them, except that of El- 

 kington and Uuolz, are, he contends, proved to be of practical value in the 

 conditions above mentioned. 



Lastly, he states that as uniform corrosion cannot be ensured in the case 

 of iron ships, and as local action is liable to produce fatal accidents at un- 

 looked-for moments, protection from corrosion and fouling, must be consi- 

 dered essential to the safety of iron ships ; if so protected, the author con- 

 tends that they are safer in every respect than the best vessels constructed 

 of timber. He also gives instances from various authorities of the rapidity 

 with which foulness accumulates on ships' bottoms, even of wood, and more 

 so if of iron, and dissents as to the possibility of removing the fouling of 

 iron ships by any scraping process, unless performed in the dry dock, and 

 constantly repeated. 



l| The communication concludes with some observations, as to the presumed 

 differences in the rate of corrosion, between railway bars in use and out of 

 use, or traversed in one or in both directions. Upon this subject the author 

 has experiments in progress on several railways, and expects at a future time to 



lay the results, as to the amounts of loss by corrosion and abrasion, before 

 the Institution ; at present his belief is that railway bars, being otherwise in 

 the same condition, corrode alike, whether travelled over or not. 



Remarks. — Dr. Ure said that the part of Mr. Mallet's paper which was 

 most interesting to chemists, was the mode of analysis. This was always a 

 subject of delicacy, difficulty, and labour. His own mode of analyzing cast- 

 iron was somewhat analogous to that which had been described. He took a 

 portion of iron, reduced by filing to a fine powder, mixed it with the same 

 quantity of chlorate of potash, and five or six times its weight of clean sili- 

 ceous sand, to dilute the mixture : this was heated in the usual way, in a 

 combustion tube with more chlorate of potash, whereby all the carbon con- 

 tained in the iron was converted into carbonic acid, which was passed through 

 a solution of the sub. acetate of lead, instead of potash water. Carbonate 

 of lead was thus produced, and its amount, when washed and dried, gave the 

 quantity of carbon in the iron operated upon, 134 parts of carbonate of lead, 

 indicating 6 parts of carbon ; therefore -j-^th of a grain of carbon might be 

 detected by this method. The question as to the state in which the carbon 

 existed in the iron was more difficult of solution. Karsten's mode of deter- 

 mining this point was very delicate and accurate : the pulverized iron was 

 mixed with moistened chloride of silver, which acted upon the metallic iron 

 alone, leaung the carburet of iron untouched, and its amount could thus be 

 determined with great nicety. With white iron which could not be filed, 

 the chloride of silver was formed into a mass. A disc of it being placed at 

 the bottom of a vessel with a little water over it, the piece of iron was laid 

 upon it; a few drops of muriatic acid were then added, and in eight or ten 

 days the iron was dissolved, leaving untouched the carbon, which existed in 

 the form of graphite. 



Mr. Williams agreed in the advantage of preventing the corrosion of iron 

 vessels, but he feared the expense of the mode proposed by Mr. Mallet, par- 

 ticularly as at present, although comparatively unprotected, they were very 

 durable. He instanced particularly the light boats on the river Shannon, 

 which, although constructed of very thin iron, and had been at work between 

 six and seven years, exhibited no signs of decay. 



Mr. Uendel said that the durability of iron canal boats was well known. 

 On the Tavistock canal, there now existed some boats which had been em- 

 ployed for 25 years in carrying coals, iron, and copper ores, or other goods, 

 and yet they were not extensively corroded. 



Mr. Field stated, that although in India iron generally corroded rapidly, 

 the iron vessels that had been sent there, did not appear to be affected 

 sooner than in England. He had been informed by Mr. Laird, that the 

 boilers of the Garry Owen iron steamer, had been renewed twice in nine 

 years, and on every occasion it had been remarked, that although the bot- 

 toms of the boilers were entirely destroyed, the iron plates of the bull of 

 the vessel immediately beneath them retained their original coat of paint, 

 and were not at all corroded. 



Mr. Jordan suggested the probability of the hull of the vessel being pro- 

 tected at the expense of the boilers, on account of the electric character of 

 the metal being altered by the heat of the boiler, and the general circum- 

 stances induced. 



Mr. Field said that the boilers in question had lasted as long as they would 

 have done on board a timber-built vessel. 



Mr. Williams corroborated .the statement. The boilers had worn out in 

 the regular time, and bad failed first in the usual spot, which was the bent 

 plate, where the sides joined the bottom. There was not any thing remark- 

 able in the wear of the boilers. 



Dr. Ure thought that the heat of the boilers having probably been suffi- 

 cient to dry up any moisture from beneath them, might have tended to pre- 

 serve the hull of the vessel from corrosion in that spot. It was easy to ac- 

 count for a less degree of corrosion taking place in iron ships, or on rails of 

 railways, as long as the former were constantly kept moving, and the latter 

 were regularly travelled over. In these cases any oxydation which took 

 place was rubbed off as it was formed; but if either were in a state of in- 

 activity, the scale of rust permitted an accumulation of moisture beneath it, 

 an active galvanic pile was completed, and oxydation went on with increased 

 rapidity. 



Mr. Vignoles remarked that the paper did not notice the iron water-tight 

 hulk-heads for vessels, which had been introduced by Mr. C. W. Williams. 

 Their practical utility was now generally admitted, and he believed they were 

 about to be adopted in the navy. 



Mr. Williams said that about nine years since, he first introduced the 

 system of dividing the hull into five compartments, by four water-tight iron 

 bulk-heads, with the intention of their adding to the strength of wooden 

 vessels; but it occurred to him that they would he otherwise useful, and al- 

 though the ship builders opposed it, he persevered, and now all the vessels 

 under his superintendence had them. Their value had been proved on many 

 occasions, and by them, the Rmjal William and several other vessels bad 

 been saved. With four hulk-heads it was impossible for a vessel to sink, 

 unless three of the compartments were broken into, which was scarcely pos- 

 sible. 



The President believed that the James Walt, which was built at least 10 



