1842.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



27-5 



0>' THE Action of Air and Water on iron. By Mr. JIallet. 



This is the third rejiort for which the association is indebted to Mr. XIallet. 

 The ohject of former tabulated results was to determine the actual loss by 

 corrosion in a given time, and the com])arative durabilities of rust of the 

 principal kinds of cast iron of Great Britain, and to discover on what dura- 

 bility depended. The tables of experiments now presented show that the 

 rate of corrosion is a decreasing one in most cases, and that the rapidity of 

 the corrosion in cast iron is not so much dependent upon the chemical con- 

 stitution of the metal as upon its state of crystalline arrangement, and the 

 condition of its constituent carbon. The present report, too, extends the 

 inquiry to wrought iron and steel, of whicli between thirty and forty varieties 

 have been submitted to experiment. The results show that the rate of cor- 

 rosion of wrought iron is in general much more rapid than that of cast iron 

 or of steel. The finer the wrought iron is, and the more perfectly uniform 

 in texture, the slower and the more uniform is its corrosion. Steel corrodes 

 in general more slowly, and much more uniformly, than wTought or cr.st iron. 

 The results of the action of air and water in the several classes of iron have 

 been examined and chemically determined. The substance spoken of as 

 plumbago was next described. It is produced hy the action of air and water 

 on cast steel, especially that in the raw ingot, in the same way as it is in the 

 case of cast iron. 



A quantity of plumbago, found in the wreck of the Royal Geori/e, absorbed 

 oxygen on exposure to the air with such rapidity, that it became nearly red- 

 hot. Mr. Mallet next described a method of protecting iron by a modification 

 of the zinc process. It was found impossible to cover the surface of iron with 

 zinc, to which it had no affinity. The first process was to clean the surface 

 of the iron, taking off the coat of oxide, and then immersing it in double 

 chloride of zinc and ammonium, which covered it with a thin film of hydro- 

 gen, by which its affinity for the zinc is much increased. The iron was then 

 covered with a triple alloy of zinc, sodium and mercury. Mr. Mallet produced 

 several specimens of his alloy, one of a bolt to be driven into a ship's side, 

 and another a cannon shot covered with his prepai'ation, and exposed to the 

 weather on the roof of a building, and which was perfectly preserved. Cannon 

 balls were so much oxidised by exposure to atmospheric influences, that in 

 five or six years they became useless. The French Institute had been engaged 

 in experiments to protect these, and had been compelled to abandon it. Mr. 

 Mallet also brought under the notice of the section a method of preventing 

 the fouling which takes place on the bottoms of iron ships, especially in 

 tropical climates, by means of which new invention he had ascertained plants 

 and animals were prevented from adhering to the ship's bottom. 



Another series of experiments related to the rate of corrosion of cast iron, 

 ■vrrought iron, and steel, exposed to atmospheric influences — a matter of great 

 importance to the engineer. The characteristic form of corrosion in air, as 

 contradistinguished from that of water, was also pointed out. This series 

 of inquiries was now complete. The next matter which had engaged his 

 attention was the rate of corrosion of rails on railways. The general opinion 

 •was, that the rails travelled over were not corroded at all. He had been 

 enabled to lay down three sets of rails on the Dublin and Kingstown Railway : 

 one not travelled over, the second in use and not exposed to corrosion, and 

 the third also in use, but made impervious to moisture. The loss of the first 

 was 2-o55, of the second '2-344, and of the third '2-650, — results which 

 seemed to indicate that the rail travelled overdoes corrode more slowly than 

 that out of use. Mr. Mallet concluded by referring to Mr. Nasmyth's theory, 

 that corrosion is checked by the trains passing over the rails always in one 

 direction, and takes place when, as in the case of the London and Blackwall, 

 trains pass both ways. ^ 



Tl>e Vice-President paid a high compliment to Mr. Mallet on the value of 

 his investigations, and the success which had attended them. The cost to the 

 association of these inquiries was far less perBaps than that incurred by Mr. 

 Mallet in addition to the sum voted him ; while the results might have been 

 made more conducive to his private purposes, had Mr. Mallet chosen to 

 conduct them for his private advantage. In reply to a member, Mr. Mallet 

 said his preparation for the bottoms of iron vessels lasted for about two years 

 and a half in Kingston harliour, in a vessel exposed to a rapid tide-way. He 

 did not think his preparations would answer for copper sheathing. Nothing 

 but copper would protect wood ; but he looked forward to the time wlien the 

 greater proportion of our vessels would be constructed of iron. 



" On the mode of conducting experiments on the resistance of air." Bv 

 Mr. Eaton Hodgkinson, F.R.S. 



Mr. Hodgkinson said, that, having been honoured by the .Association with 

 a request to pursue some experiments on the resistance of the air, he was 

 desirous of exhibiting an instrument prepared for making the first series of 

 these experiments. He proposed, in the first instance, to seek for the force 

 of the wind moving at different velocities, upon plane surfaces of given di- 

 mensions, these surfaces being either perpendicular, or inclined at any angle, 

 to its current ; to determine this, he intended to ])Iace the apparatus upon 

 the front of the first carriage of a railway train ; the road along which the 

 train passed having for a short distance poles stuck up, one hundred or two 

 hundred yards asunder. He would try the experiment only on days when 

 there was no perceptible wind ; and then, if the time in seconds, taken in 

 passing between two poles, be carefully observed, and the pressure indicated 

 upon the discs (which were of two feet and four feet area, both roimd and 

 square), the resistance per square foot, with a given velocity, wou'.d be o! - 



tained. He hoped to determine these facts, with various velocities and at 

 different angles of inchnation in the discs, trying the same experiments with 

 both discs at the same time, to ascertain whether the resistance to a square 

 surface and a round one, of equal area, was the same, and that the results 

 might correct each other. It would then be determined how far the law of 

 resistance of air to planes moving obliquely through it agreed with the theo- 

 retical suppositions hitherto in use. To apply the result of the proposed ex- 

 periments to the case of bodies at rest, acted upon by the wind, he assumed 

 that the resistance of a body moving with a given velocity through the air 

 at rest, was the same as that of the wind moving with the same velocity, and 

 acting upon the body at rest. The directors of the Manchester and Bir- 

 mingham Railway had kindly consented, at Mr. Buck's request, to allow him 

 to make these experiments ; and he was indebted to Mr. Fairbairn for the 

 apparatus, — This was placed on the table. It consists of two discs of wood 

 (which may be round, square, or of any other form), made inclinable to any 

 ancle, by means of screws that fix them to their position, and having two 

 straight rods moving in slots, and an attached quadrant to measure the 

 angle. To ascertain the force of the wind, one of Salter's balance springs is 

 placed behind each disc, attached to the cross piece which connects the two 

 rods of the discs ; and this indicated the force of the wind at any moment. 

 Several suggestions were made as to the instrument, and the mode of trying 

 the experiments ; to which Mr. Hodgkinson said he would give every con- 

 sideration. 



Experimental Inquiries on the Strength of Stones and other 

 Materials. By Mr. Hodgkinson. 



After noticing the present state of knowledge on this subject, and the 

 experiments of Barlow, Rennie, and of other experimentalists on the con- 

 tinent, Mr. Hodgkinson said he had long felt anxious to ascertain how the 

 three forces — the crushing, the tensile, and the transverse strength — and the 

 position of the neutral line — (that separating the extended and compressed 

 fibres in a bent body) — were connected in bodies generally ; and his experi- 

 ments had for several years been directed to discovering facts upon each of 

 these matters, in order to determine the question. His experiments some 

 years ago, made for the British Association, with respect to the values of hot 

 and cold blast iron, had shown that the ratio of the forces of ultimate tension 

 and compression was nearly constant in all the species of cast iron ; and a 

 few experiments made at that time on sandstone and marble, had led him to 

 suspect that nearly the same would be the case in these and other hard 

 bodies. Through the liberty of his friend Mr. Fairbau-n (who had, as usual, 

 given him every assistance his establishment afforded), he (Mr. Hodgkinson) 

 had made a great many experiments upon wood, sandstones, marbles, glass, 

 slate, ivory,^bone, &.Q., to ascertain the tensile, crushing the transverse 

 strength of each ; also, as far as possible, the situation of the neutral line in 

 thirteen different kinds of timber (including oaks, pines, teak, &c.) All the 

 three sorts of experiments w-ere made as far as possible out of the same 

 specimen in each case, to render the results as unexceptionable as they could 

 be made. The wood was of good quality and perfectly dry, having been 

 chosen for this purpose, and laid in a warm dry place for four years or more. 

 Previous to experiment, the bars of wood were all reduced with care to the 

 same dimensions, and afterwards weighed, to ascertain the specific gravity. 

 They were then laid upon supports to obtain the deflections with given 

 weights, and the breaking weight with its deflection. The two portions into 

 which a specimen was broken were afterwards reduced in the middle by the 

 lathe to the form used in Mr. Barlow's experiments, in order that the experi- 

 ments might be torn asunder in the middle, by a force acting directly through 

 the axis, and thus to obtain the tensile strength of the wood. Afterwards, 

 the thick ends of the specimens were turned by the lathe into cylinders, all 

 of the same diameter and length, as nearly as practicable, and their exact 

 dimensions afterwards taken, in order to ascertain by experiment the resist- 

 ance of the woods to a crushing force. After describing the character and 

 results of his experiments on the various substances named above (specimens 

 of -which he produced), Mr. Hodgkinson gave the following summary of 

 results of very numerous experiments on marbles and stones of various 

 degrees of hardness : — 



Crusliing force per square inch 

 called 1000. 



Transverse strength 

 Tensile force of bar 1 inch square, 

 Desciption of stone. per sqr. inch, and 1 loot spaces. 



Black marble H3 10-1 



Italian marble 84 10-6 



Rochdale flagstone l"* 9 9 



High .Moor stone lO" 



Stone called Yorkshire flag .... _ 9 S 



Stor.e from Little HuUon, near Bolton 70 8 S 



Mean rates 100 9'8 



Mr. Hodgkinson gave the following recapitulation of results :— Calling the 

 mean crushing strength per square inch, in the different articles experimented 

 upon, 1000, we have — 



