TRANSACTIONS OP SECTION B. 595 



the method of heating by radiation is, of course, the result of purely theoretical 

 considerations. 



The progress in the methods of extracting the precious metals has heen very 

 great, both on the chemical and engineering sides, but it is curious that in the 

 metallurgy of gold and silver many ancient processes survive which were arrived 

 at empirically, — a noteworthy exception being presented by the chlorine process 

 for refining gold, by the aid of which many millions sterling of gold have been 

 purified. The late Mr. H. B. Miller based this process for separating silver from 

 gold on the knowledge of the fact that chloride of gold cannot exist at a bright 

 red heat. The tension of dissociation of chloride of gold is high, but the precious 

 metal is not carried forward by the gaseous stream, at least not while chloride of 

 silver is being formed. 



The influence of scientific investigation is, however, more evident in that por- 

 tion of the metallurgic art which deals with the adaptation of metals for use, rather 

 than with their actual extraction from the ores. 



Only sixteen years ago Sir Nathaniel Barnaby, then Director of Naval Construc- 

 tion, wrote, ' our distrust of steel is so great that the material may be said to he 

 altogether unused by private ship-builders .... and marine engineers appear to 

 be equally afraid of it.' He adds, ' the question we have to put to the steel makers 

 is, what are our prospects of obtaining a material which we can use without such 

 delicate manipulation and so much fear and trembling ? ' All this is changed, for, 

 as Mr. Elgar informs me, in the year ending on June 30 last, no less than 401 

 ships, of three quarters of a million gross tonnage, were being built of steel in the 

 United Kingdom. 



Why is it, then, that steel has become the material on which we rely for our 

 ships and for our national defence, and of which such a splendid structure as the 

 Forth Bridge is constructed ? It is because side by side with great improvement 

 in the quality of certain varieties of steel, which is the result of using the open- 

 hearth process, elaborate researches have shown what is the most suitable 

 mechanical and thermal treatment for the metal ; but the adaptation of steel for 

 industrial use is only typical, as the interest in this branch of metallurgy gene- 

 rally appears for the moment to be centred in the question whether metals can, like 

 many metalloids, pass under the application of heat or mechanical stress from a 

 normal state to an allotropic one, or whether metals may even exist in numerous 

 isomeric states. 



It is impossible to deal historically with the subject now further than by stating 

 that the belief in more than one ' modification ' is old and widespread, and was ex- 

 pressed by Paracelsus, who thought that copper 'contains in itself its female,' 

 which could be isolated so as to give ' two metals '....' difierent in their 

 fusion and malleability' as steel and iron difier. Within the last few years 

 Schiitzenberger has shown that two modifications of copper can exist, the normal 

 one having a density of 8'95, while that of the allotropic modification is only 8'0, 

 and is moreover rapidly attacked by dilute nitric acid which is without action on 

 ordinary copper. It may be added that Lord Eayleigh's plea for the investigation 

 of the simpler chemical reactions has been partly met, in the case of copper, by 

 the experiments conducted by V. H. Veley on the conditions of chemical change 

 between nitric acid and certain metals. 



Bergmann, 1781, actually calls iron polymorphous, and says that it plays the 

 part of many metals. ' Adeo ut jure dici queat polymorphum ferrum plurium 

 simul metallorum vices sustinere.' Osmond has recently demonstrated the fact 

 that at least two modifications of iron must exist. 



Professor Spring, of Liege, has given evidence that in cooling lead-tin alloys 

 polymerisation may take place after the alloys have become solid, and it seems to 

 be admitted that the same cause underlies both polymerisation and allotropy. 

 The phenomenon of allotropy is dependent upon the number of tlie atoms in 

 each molecule, but we are at present far from being able to say what degree of 

 importance is to be attached to the relative distance between the atoms of a metal 

 or to the ' position of one and the same atom ' in a metallic molecule, whether 

 the metal be alloyed or free ; and it must be admitted that in this respect organic 



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