568 



NA TURE 



\_April 14, 1 88 1 



which had not been so treated, but had simply been left undis- 

 turbed in the apparatus. The positive quality thus produced by 

 the hydrogen diminishes gradually, and becomes insensible after 

 two or three days.] 



P.S. — On December 24, iSSo, one of two platinum plates in 

 the Volta-condenser was taken out ; placed iu dried oxygen gas 

 for forty-five minutes ; taken out, carried by hand, and replaced 

 in the Volta-condenser at 12.30 on that day. It was then found 

 to be negative to the platinum plate, which had been left undis- 

 turbed. The amount of the difference was about '33 of a volt. 

 The plates were left undisturbed for seventeen minutes in the 

 condenser ; and were then tested again, and the difference was 

 found to have fallen to '29 of a volt. At noon on the 

 25th they were again tested, and tlie difference found to be 

 ■iS. The differences had been tested from time to time since 

 that day, the plates having been left in the condenser undisturbed 

 in the intervals. The following Table shows the whole series of 

 these results : — 



Electric difference between 

 surfaces of a platinum plate in 

 Time. natural condition, and a platinum 



plate after 45 minutes' exposure 

 to dry oxygen gas. 

 ■33 of a volt. 

 ... -29 

 ... -iS 

 ... -116 „ 

 ... -097 „ 

 ... -047 „ 

 ... -042 „ 

 ... '020 ,, 



Mr. Rennie, by whom these experiments were made during 

 the recent Christmas holidays, had previously experimented on a 

 platinum plate which had been made the positive pole in an 

 electrolytic cell with an electromotive force of one volt, tending 

 to decompose water acidulated with sulphuric acid ; the other 

 pole being a piece of platinum wire. After the plate had been 

 one hour under this influence in the electrolytic cell he removed 

 It, and dried it by lightly rubbing it with a piece of linen cloth. 

 He then placed it in the Volta-condenser, and found it to be 

 negative to a platinum plate in ordinary condition ; the difference 

 observed was "27 of a volt. _ This experiment was made on 

 October 21 ; and on November S it was found that the difference 

 had fallen from '27 to '07. Mr. Rennie also made similar expe- 

 riments with the platinum disk made the negative pole in an 

 electrolytic cell, and found that this rendered the platinum 

 positive to undisturbed platinum to a degree equal to about '04 

 of a volt. The effect of soaking the platinum plate in dry 

 hydrogen gas, alluded to in my first postscript, which also «as 

 observed by Mr. Rennie, was found to be about "li of a volt. 

 Thus in the case of polarisation by hydrogen, as well as in the 

 case of polarisation by oxygen, the effect of exposure to the dry 

 gas was considerably greater than the effect of electro-plating the 

 platinum with the gas by the electromotive force of one volt. 



THE NA VAL ARCHITECTS 

 'T'HE session of the Institution of Naval Architects just con- 

 eluded was remarkable for the number of papers on the 

 use of steel both for .shipbuilding and marine engineering. This 

 was perhaps to be expected in consequence of the commotion 

 among steel-users caused by the total failure of the steel plates 

 supplied for the boilers of the Russian yacht Livadia. Accord- 

 ingly we find four papers on this subject. The first, by Mr. 

 Samuda, deals with the effect which the introduction of steel hulls 

 and steel-faced armour has had upon the design of ships of war. 

 This paper is based upon the results attained by the author with 

 a steel corvette which he has recently constructed for the Argen- 

 tine Government. The dimensions of this vessel as actually 

 constructed, and the corresponding dimensions which must of 

 necessity have been adopted, had the material of construction 

 been iron instead of steel, should be carefully noted in order 

 to appreciate the true benefits to be derived from the use of the 

 latter material. 



The vessel as actually constructed is 240 feet long by 50 feet 

 wide ; the displacement is 4200 tons, the power 4500 horses, and 

 the coal-supply 650 tons, which is sufficient to allow her to steam 

 6000 miles at a speed of S knots, or 4300 miles at a speed of 10 

 knots. The speed which it is expected will be attained on the 

 measured mile is 13I knots. If the vessel had been built of 

 iron and cased with iron armour, the speed and shot-resisting 



power remaining the same, the dimensions would have been as 

 follows : — Length, 260 feet ; breadth, 55 feet ; displacement, 

 5200 tons ; power, 5000 horses ; and coal-supply, 720 tons. 

 This example is a very good illustration of the great benefit 

 which naval architects will derive from the use of steel, a benefit, 

 be it remarked, which comes most opportunely in these days of 

 ]iowerful ordnance ; for not only has the steel-faced armour 

 about 25 per cent, more re^iiting power than an equal thickness 

 of iron, but also the weight saved in the hull and machinery by 

 the use of steel enables a greater quantity of armour to be 

 carried. 



The second paper on steel was by Mr. W. Parker, Chief 

 Engineer Surveyor to Lloyd's Registry, " On the Causes of the 

 Failure of the Steel Plates supphed for the Boilers of the Livadia." 

 Steel, as is well known, had formerly a bad reputation for 

 treachery and uncertainty of behaviour. Latterly however a 

 more intimate knowledoe of the methods of manufacture and a 

 better acquaintance with the processes of working had apparently 

 quite removed this impediment to its general introduction. The 

 failure therefore above referred to came as a surprise to ship- 

 builders, and the circumstances demanded and received a most 

 searching inquiry at the hands of the engineer officers of Lloyd's. 

 It was found that samples cut from the broken plates fulfilled 

 every test demanded by Lloyd's, the Admiralty, and the Board 

 of Trade. The tensile strength proved to vary between the very 

 narrow limits of 26"i and 28'3 tons per square inch. The 

 elongation after fracture of samples 8 inches in length ranged 

 from 27*3 to 34'3 per cent. Nevertheless in spite of the appa- 

 rently excellent quality of the plates, it was found that after they 

 had been punched and worked into place they had become so 

 brittle as to be unable to stand the hydraulic proofs to which it 

 is usual to subject boilers, and in some instances even, the plates 

 cracked before the hydraulic test was applied. The further 

 investigations of Mr. Parker proved that wlienever samples of 

 the plates were punched, the material became so brittle as to 

 break into pieces under the blow of an ordinary sledge-hammer ; 

 the tensile strength dropped to l8"4 tons per square inch, and 

 the extensibility disappeared altogether. 



Specimens were next subjected to chemical analysis, with the 

 result of proving that, the material was from the chemical point 

 of view far from homogeneous. A portion of tlie plates, about 

 8 inches long by 4 inches wide, was carefully freed from rust by 

 grinding, and successive layers were planed off from one side to 

 the other. Lach layer was one-sixteenth of an inch in thickness, 

 and they were numbered iu succession as they were planed off. 

 The result of analysis showed that the quantities of carbon, 

 manganese, sulphur, and phosphorus varied in an extraordinary 

 di gree. These differences in the chemical composition, how- 

 ever, did not satisfactorily account for the behaviour of the metal. 

 It was not till the apijearance of the fractures suggested, tliat 

 the material had not been properly worked under the hammer 

 and rolls, that a really satisfactory solution of the mystery was 

 arrived at. "A piece cut from the fractured plate was raised to a 

 red heat and rolled to half its original thickness. Strips vvere 

 then cut from this f inch plate, and punched with holes 5 inch 

 diameter, being one half the size of those in the f-inch plate. 

 This extra work on the material seemed to raise its ductility 

 appreciably, the strips being found to bend well after punching, 

 several of them bending to right angles, and only one of them 

 breaking short off, while none of them showed such extraordi- 

 nary signs of brittleness as « ere observable in the material when 

 of the original thickness. Three pieces tested for tensile strength 

 after rolling broke under a stress of 33 tons, 34"2S tons, and 

 32"3 tons per square inch respectively, with an elongation in 

 8 inches of 12 percent., 11-25 per cent., and 17-5 per cent, 

 respectively, the last-mentioned specimen being annealed." 



Mr. Parker concludes his paper by expressing the hope that 

 the facts which he was able to lay before the meeting will tend 

 to allay alarm and to strengthen confidence in the use of mild 

 steel for constructive purposes. When it is considered what an 

 enormous quantity of this material is now being used in the con- 

 struction of marine boilers, as well as for the hulls of vessels, 

 this wish will be heartily re-echoed. In the spring of 1878 

 there were only two marine boilers of the modern form made of 

 mild steel in existence. Within twelve months subsequently to 

 that date 120 steamers had been fitted with boilers of this 

 material, and during the same period in the following year 280 

 vessels more. At the present moment there are no less than 

 1 100 steel boilers in use in steamships, weighing together "v-r 

 17,000 tons. 



