1 



512 



NATURE 



{Sept. 19, 1889 



of a substance are all that is needed, and the requisite purity can 

 be obtained at a moderate cost of time and labour ; but when 

 mechanical properties have to be determined considerable masses 

 are needed, and the funds necessary for obtaining these are 

 beyond the reach of most private individuals. I cannot help 

 suggesting that wealthy institution^, such as many of those con- 

 nected with our profession, could not employ their resources 

 more wisely than in giving the means of following up the 

 researches which Prof. Roberts- Austen has inaugurated. 



In view of the difficulty of obtaining metals of sufficient purity, 

 he selected gold as his base, because that metal can be more 

 readily brought to a state of purity than any other, and is not 

 liable to oxidation. In a communication to the Royal Society, 

 made last year, he shows that the metals alloyed with gold which 

 diminish its tenacity and extensibility have high atomic volumes, 

 while, those which increase these properties have either the same 

 atomic volumes as gold or have lower ones. The inquiry has 

 only just been commenced, but it appears to me to promise 

 results which, to the engineer, will prove as important and as 

 fruitful of progress as the great generalization of Mendeleeff has 

 been to chemists. A law which can not only indicate the exist- 

 ence of unknown elements but which can also define their 

 properties before they are discovered, if capable of application 

 to metallurgy, must surely yield most valuable results, and will 

 make the compounding of alloys a scientific process instead of 

 the lawless and haphazard operation which it is now. 



The practical importance of the views I have enunciated are, : 

 I think, sufficiently obvious. Everyone will admit that an 

 external force cannot be applied to a system in motion without ; 

 affecting that motion ; consequently matter, in whatever state, 

 cannot be touched without changes taking place, which will be 

 more or less permanent. The application of heat will cause a 

 change of volume, and, at last, a change of condition ; the 

 application of external stresses will also produce a change of 

 volume ; and it is natural to infer that there must be some relation 

 between the two, and, accordingly, Prof. Carnelley has drawn 

 attention to the fact that the most tenacious metals have 

 high melting-points, though here again there is a great want 

 of exactness, partly on account of the difficulty of measuring 

 high temperatures, and partly by reason of the scarcity of pure 

 materials. 



Again, long-continuei stresses, or stresses frequently applied, 

 may be expected to produce permanent changes of form, and so 

 we arrive at what is termed the fatigue of substances. Stretched 

 beyond their elastic limits, which limits I do not suppose to exist 

 except when stresses are applied quickly, substances are perma- 

 nently deformed, and the same effects follow the long applica- 

 tion of heat. The constant recurrence of stresses, even of those 

 within the elastic limit, causes changes in the arrangement 

 of the molecules of substances which slowly alter the pro- 

 perties of the latter, and in this way pieces of machinery, 

 which theoretically were abundantly strong for the work they 

 had to perform, have failed after a more or less extended period 

 of use. The effect is intensified if the stresses are applied sud- 

 denly, if they reach nearly to the elastic limit, and if they are 

 imposed in two or more directions at once, for then the mole- 

 cular disturbance becomes very intense, the internal equilibrium 

 is upset, and a tendency to rupture follows. Such cases occur 

 in artillery, in armour-plates, in the parts of machinery subject 

 to impact ; and, as might be expected, the destructive effects do 

 not always appear at once, but often after long periods of 

 time. 



When considerable masses of metal have to be manipulated 

 by forging or by pressure in a heated condition, the subsequent 

 cooling of the mass impose-; restrictions on the free movement of 

 some, if not all, of the particles ; internal stresses are developed 

 which slowly assert themselves, and often cause unexpected 

 failures. In the manufacture of dies for coining purposes, of 

 chilled rollers, of shot and shell hardened in an unequal manner, 

 spontaaeous fractures take place without any apparent cause, 

 and often after long delay, the reason being that the constrained 

 molecular motion of the inner particles gradually extends the 

 moti:)n of the outer ones until a solution of continuity is 

 caused. 



Similar stresses occur in such masses as crank shafts, screw 

 shafts, gun hoops, &c. The late General Kalakoutsky, some 

 seventeen years ago, commenced a systematic investigation into 

 the internal stresses in the tubes and hoops of guns and in 

 armour-piercing shells. The method he pursued was to cut disks 

 ■or i-ings about half an inch thick off the hoops and shells, 



to divide the metal of each disk into from four to six rings, to fix by 

 means of silver plugs, on which very finely marked cross-lines were 

 drawn, from four to eight points on the surface of each ring, and 

 then to measure, with extreme exactness, the changes in dia- 

 meter produced in every ring by the successive cutting out of the 

 rings. Knowing by direct tests the mechanical properties of his 

 material, he was able, from the changes in the diameters, to 

 calculate what the tangential stresses in every part of each disk 

 were, and to draw inferences as to their fitness for the work they 

 were intended to perform. The same method of investigation 

 has been pursued by Captain Noble of the Elswick Works, and 

 by Lieutenant Crozier of the United States Artillery, with the 

 practical result that probably much more attention will be paid 

 in future to the principles on which the annealing and hardening 

 of steel is carried on. A gun hoop or tube, to be in the best 

 condition to resist a bursting stress, should have its inner surface 

 in a slate of compression, and its outer in a statQ of tension, and 

 the hoops should be shrunk on to the tubes or on to each other 

 with but very little pressure. General Kalakoutsky proposed, 

 in order to set up beneficial internal stresses, that tubes which 

 were being annealed should be cooled from the inside by a jet 

 of steam, of air, of water, or of oil ; and he advocated the practice 

 of testing the effects of each new method of manufacture or of 

 treatment by the careful measurements of slices of the finished 

 material instead of working at random, as is still very much 

 the practice. It is evident, also, that a sample of steel cut out 

 of a gun hoop or crank shaft, and tested, can afford no indication 

 of the available tenacity of the same sample in situ. When 

 released from the constraint of its surroundings, the particles 

 must, of necessity, change their condition, for the disturbing 

 forces have been removed ; and the probability is that, if the 

 steel be good, the test will prove satisfactory, especially if some 

 time be allowed to elapse between cutting out the sample and 

 testing it, and a false security will be engendered such as has 

 often led to disastrous results. 



The influence of time on steel seems to be well established ; 

 the highest qualities of tool steel are kept in stock for a 

 considerable period ; and it seems certain that bayonets, swords, 

 and guns are liable to changes which may account for some of 

 the unsatisfactory results which have manifested themselves at 

 tests repeated after a considerable interval of time. As all these 

 things have been hardened and tempered, there must necessarily 

 have been considerable constraint put upon the freedom of 

 motion of the particles, this constraint has gradually been over- 

 come, but at the expense of the particular quality of the steel 

 which it was originally intended to secure. 



I have now laid before you the views respecting the consti- 

 tution of matter which I think are gaining ground, which explain 

 many phenomena with which we are familiar, and which will 

 serve as guides in our treatment of metals, and especially of 

 alloys ; but I must admit that the subject is still by no means 

 clear, that a great deal more definition is wanted, and that we 

 are still awaiting the advent of the man who shall do for 

 molecular physics what Newton did for astronomy in explaining 

 the structure of the universe. 



One of the most remarkable features of the last thirty years is 

 the introduction of petroleum, and the wonderful development 

 to which the trade in it has attained. 



Under the generic name of petroleum are embraced a vast 

 variety of combinations of carbon and hydrogen, each of which 

 is distinguished by some special property. At ordinary tempera- 

 tures and pressures some are gaseous, some are liquid, and some 

 solid, and most are capable of being modified by suitable treat- 

 ment under various temperatures and pressures. The employ- 

 ment of petroleum in the arts is still extending rapidly. Used 

 originally for illuminating purposes, it is now employed as fuel 

 for heating furnaces and steam-boilers ; as a working agent in 

 heat-engines ; valuable medicinal properties have been discovered ; 

 and as a lubricant it stands unrivalled. 



As an illuminant, even in this country, it is, to a large extent, 

 superseding every other in private houses, and even in public 

 lamps, because it gives a cheaper and more brilliant light than 

 ordinary gas, and leaves the consumer free from the tyranny of 

 great and privileged companies. 



As fuel it is especially convenient, cleanly, and economical. 

 Stored in tanks of suitable construction, it is sprayed into the 

 furnace without labour and without creating dust and dirt ; 

 it is especially convenient in locomotive and marine work on 

 account of the rapidity, ease, and cleanliness with which it can be 



