190 



THE CIVIL ENGINEER AND ARCHITECrS JOURNAL. 



[Mat, 



seilles, the cast iron of which the propeller was composed, was found to have 

 undergone considerable change, and to have become so soft, that it could be 

 cut with a knife. 



Mr. Grantham believed, that circumstance was owing to the cast iron pro- 

 peller, working too near the copper sheathing of the vessel. Iron vessels 

 would not be liable to that objection. The amount of oxydation was ap- 

 parently increased, by the cast iron remaining in a state of rest ; now as 

 screw propellers were usually in rapid rotation, and were also generally so 

 constructed that they could be unshipped, they could be painted and pre- 

 served from any injurious amount of external corrosion, although a chemical 

 change might still be induced, when the cast iron was in contact with 

 copper. 



General Pasley had observed, in the metal raised from the wrecks of the 

 Edgar and the Royal George, ' that the cast iron was generally soft, and in 

 many instances resembled plumbago; that when small pieces were cut from 

 any of the iron guns, or that these pieces were pounded in a mortar, heat 

 was evolved, but after two or three days the metal cooled again ! some of the 

 shot which had been found had burst into several pieces, under this heating 

 action. * The wrought iron was not so much injured, except when it was 

 in contact with copper, or gun-metal ; some of it appeared to have under- 

 gone an unequal action, and presented a reticulated surface, as if the softer 

 portions had been destroyed, leaving the harder fibres uninjured. ^ Those 

 portions of the wrought iron, which were used by the smiths in the Dock- 

 yards, were declared to be of a better quality than any modern iron. Neither 

 the copper, nor the gun-metal, were much acted upon, unless they were in 

 contact with iron. 



Mr. Cottam had observed, with great attention, the iron guns which were 

 brought from the Royal George to the Tower ; when they arrived, they were 

 soft, and could be easily cut with a knife ; ' ° but when he examined them 

 some time afterwards, the metal bad resumed its original hardness. This 

 was frequently the case with" pump-trees, which had become soft, from im- 

 mersion in mineral water, but on being taken out and laid aside for a time, 

 they became hard again. 



Mr. Galloway stated, that this spontaneous development of heat by cast 

 iron, which had been long immersed in salt water, had been frequently ob- 

 served. A striking instance of this kind occurred at Woolwich, when an 

 attempt was made, to preserve the copper sheathing of vessels from corro- 

 sion. Sir Humphrey Davy suggested to the Admiralty, that the decompo- 

 sition of the copper sheathing could be neutralized, by the application of 

 tin, zinc, or any other easily oxydable metal ; the plan was tried on several 

 vessels, by attaching to them zinc plates, and the protection was so perfect, 

 that the ships' bottom became covered with barnacles and weeds. Cast iron 

 was then substituted, on the supposition that the partial oxydation, which 

 would be permitted by the iron, would prevent the fouling of the copper, 

 but that the ordinary rapid destruction would be modified. ' ' The Magici- 

 enne frigate, having been at sea for some time, with cast iron protectors, was 

 docked at Woolwich for examination ; when it was found, that the protection 

 instead of being partial, had been local, for while the greater portion of the 

 surface of the copper was oxydized as usual, the parts contiguous to the 

 iron had been perfectly protected and were covered with barnacles. Mr. 

 Marsh (of the Ordnance department) broke off some small pieces of the 

 iron, which presented the appearance of plumbago, was easily cut, .vas 

 greasy to the touch, and left black marks upon paper ; ' = in a few minutes 

 the heat became so great, as to ignite the paper in which the pieces were en- 

 veloped. The development of heat, was generally supposed to proceed from 

 the rapid absorption of oxygen by the mass, on being brought into the air. 



1 The" Edfar" was sunk in 1711, and the "Royal George" in 1782. 



8 A similar action was observed, in the cast-iron shot raised from the " Mary Rose," 

 which was wreckad in the reign of Henry VIII. 



9 This appearance was also noticed by Mr. Mallet, and is mentioned in his paper, 

 " On the Corrosion of Iron, &c."— See " Journal," Vol. VI., p. 3t)6. 



10 Vide Trans. Inst. C.E., Vol. I., p. 20-4. 



1 ■ Vide Mr. Willtinson's paper " On the Sh?athlng of Ships," " Journal," Vol. v., p. 

 169. 



12 In Dr. Thomson's "Annals of Philosophy," are the following remarks :—" Dr. 

 Henry states, that ' cast iron having been in contact with muriate of lime, or muriate ot 

 magnesia, most of the iron was removed. The speciBc gravity woa reiluced to 2-15S, and 

 what remained was chiefly plumbago, and the usual impurities.' 



" Dr. Brande found that * a cast iron gun had uudergoue a like change, from being long 

 immersed in sea-water. To the depth of an inch it was converted into a substance, 

 having all the external character of plumbago. The component parts were— 



81 

 16 



Oxyde of iron 

 Plumbago 



a7 



" Mr. Mushet, in his work on ' Iron and Sleel,' states, that wrought iron sometimes, 

 though very rarely, undergoes the same change. 



" Professor Daniel, in the ' Quarterly Journal of Science," Vol. H., p. 290, says ' I am 

 inclined, under ali the circumstances, to believe that the triple carburet, as it is at first 

 obtained, consists of iron and silicum in the metalline state, united to carbon. When 

 brought into contact with oxygen gas, the metals become convarted to protoxydes, giving 

 out heat, without separating from the carbon.' 



" Uy analysis, he found the substance to consist of — 



Red oxyde of iron 7"0 = 6'2 black oxyde 

 4-9 sllex 

 11.2 carbon 



" The same author states an important fact, bearing on the present question, namely, 

 * that it took three times as long to saturate an acid, when it acted on white cast iron, as 

 when it acted on the grey kind.* " 



from the water, where it had already received a certain amount of oxygen" 

 The production of heat, being in this case, governed by the same law, as 

 that under which animal heat, and the heat of combustion, were developed. 



Mr. Homersham said, that the water of the Thames, up as high as Rich- 

 mond, had the same effect as sea-water, in rendering cast iron soft. 



Mr. Simpson believed, that if hard grey cast iron with a good surface, 

 was used for castings, which were subjected to the action of sea-water, but 

 little injurious effect was to be dreaded ; he was so convinced of the fact, 

 that he was about to use cast iron extensively for piles. He had recently 

 examined some cast iron piles, which had been in sea-water for 16 years, 

 without any detrimental effect being produced. 



Mr. Jordan thought that it was very desirable, to mark the difference be- 

 tween the composition of brass, and the alloy of copper and tin, used in 

 casting guns. With brass, in which zinc formed a part of the composition, 

 it was probable, that the iron would have been acted upon with less energy, 

 because it was more electro-negative than zinc ; hut the gun-metal acted 

 positively upon the iron, and apparently, altered the substance. 



Mr. Braithwaite said, that the proportions of the mixture, used for the 

 bearings of machinery, were usually 92 per cent, of copper and 8 per cent, 

 of tin. 



The President said, that although the discussion had taken a direction 

 which had not been anticipated, and was foreign to the original subject, he 

 had not attempted to lead it back again, because the question of the causes 

 of the chemical change in cast iron, in certain positions, and the means of 

 preventing it, was of the utmost importance to engineers, particularly as in 

 all modern works so much cast iron was used. 



PUMP VALVES. 



fFrem the Minutes of Proceedings of the Institution of Civil Engineers, 

 wit/i Engravings, Jigs. 11 to 13, Plate VII.) 



Mr. J. B. Jordan exhibited and described a model, showing the principal 

 pump valves, used by mining engineers. Mr. Jordan stated, that the model 

 before the meeting, was intended to illustrate mining machinery, and was one 

 of a series, now in progress of construction for the Museum of Economic 

 Geology. There were eight difl'erently constructed valves in it, each sur- 

 mounted by a glass valve-chamber and pipe ; the large central pump, served to 

 circulate the water through all the valves simultaneously, so as to show their 

 comparative action ; the water was then discharged from the collar launders 

 over each valve, into that at the head of the puu'.p, so that by repetitions of 

 the pump-stroke, the circulation through the valves might be kept up at 

 pleasure. 



The valves shown in the model might be divided into four classes: — 1st. 

 Those in which no attempt was made to counteract, or avoid the violence of 

 the beat, or concussion, on closing the valve. 2nd. Those in which that evil 

 was reduced, by dividing the horizontal area of the valve, into several parts. 

 3rd. Those in which the same object was attained, by reducing the horizontal 

 area of the moving parts of the valve. 3th. That in which the concussion 

 was reduced to any desired amount, by making one side or portion of the 

 column, to a certain degree, balance the other. 



Valves of the first class were so well known, that they required little de- 

 scription ; they were the common pump clack, moving on a leather joint, and 

 having generally a very small water way — the improved metal joint clack, in 

 which the water way was much increased — and the ' button clack,' or as it 

 was called in Cornwall ' hcantlebury's clack,' which was a disc of metal with 

 a central spill or stalk, which rose and fell in a guide. Of these valves, the 

 second was considered the best, inasmuch as it had the largest waterway 

 (some portion of which was direct), and it was free from some minor objec- 

 tions, to which the leather-jointed clack was liable. This valve was there- 

 fore in very common use in mine pumps, where the area of the pump and the 

 height of the column, were not such as to produce any serious inconvenience 

 from concussion, in closing the valve. 



In the second class of valves, the injurious efl'ect of a violent beat was 

 somewhat avoided, by the ingenious expedient, of dividing the valve into 

 several rings, or segments. The simplest of this class, was the well known 

 ' butterfly valve,' in which two semicircular parts opened on a central hinge 

 of leather, and the beat was divided into two parts ; but as those closed at 

 the same time, the concussion was principally reduced by the fall not being 

 so great. The next valve was composed of several triangular pieces, opening 

 on leather joints, from the circumference of the valve seating ; it had been 

 much used by Capt. Reed, of the Mold Mines, Flintshire, and was reported 

 of favourably, by several other mining engineers. It closed with very slight 

 concussion, on account of the are of each part being small, the base of each 

 triangle forming the joint, while the water way was large, and nearly all 

 direct, admitting the mass of water to pass forward, in line parallel to the 

 side of the pump. In the other valves of this class, no leather was used, a 

 circumstance which rendered them more applicable to large pumps, where 

 continuous working was of the utmost importance, particularly in the case of 

 deep mines. 



The two annular valves shown, were invented by Mr. Hosking of the 

 Perran Foundry, and Mr. Jenkyn of the Copper-house Foundry, (Cornwall). 

 The first of these, was composed of a series of rings working on a vertical 

 spill, each ring having its seat on the one beneath it ; (see figs. 11 and 12) ; 

 there rings have different areas, and fell in succession through a small space, 

 compared with that which would be requisite, if the valve were in one piece, 



