724 EEPORT— 1889. 



of substances is very recent, it promises to be of great importance. I allude to the 

 Periodic Law of Dr. Mendel^eff. According to that law, the elements, arranged in 

 order of their atomic weights, exhibit an evident periodicity of properties, and as 

 Professor Carnelley has observed, the properties of the compounds of the elements 

 are a periodic function of the atomic weights of their constituent elements. Acting- 

 on these views, Professor Roberts- Austen has recently devoted much time and 

 labour to testing their exactness with reference to the mechanical properties of 

 metals. The investigation is surrounded by extraordinary difficulties, because one- 

 of the essential features of the inquiry is that the metals operated on should be- 

 absolutely pure. For chemical researches, a few grains 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 institutions, such 

 as many of those connected with our profession, could not employ their resources- 

 more wisely than in giving the means of following up the researches which Pro- 

 fessor 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 generalisation of Mendel^eff has been to chemists. A law which can not 

 only indicate the existence 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 mate 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, suffi- 

 ciently obvious. Every one wUl admit that an external force cannot be applied to 

 a system in motion without afl^ecting that motion ; consequently matter, in what- 

 ever 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. Professor Oarnelley 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-continued 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 per- 

 manently deformed, and the same effects follow the long application of heat. The 

 constant recurrence of stresses, even those within the elastic limit, causes changes 

 in the arrangement of the particles of substances which slowly alter the properties 

 of the latter, and in this way pieces of machinery, which theoretically were abun- 

 dantly 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 suddenly, 

 if they reach nearly to the elastic limit, and if they are imposed in two or more 

 directions at once, for then the molecular 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 imposes restric- 



