12 



NATURE 



\_Nov. 7, 1889 



to keep these old definitions carefully in mind. I shall 

 employ the word tempering in the sense of softening, as 

 Falstaff uses it when he says of Shallow : — ■ 



"I have him already tempering between my finger and my 

 thumb, and shortly will I seal with him." ^ 



softening, that is, as brittle wax does by the application 

 of gentle heat. Hardening, then, is the result of rapidly 

 cooling a strongly heated mass of steel. Tempering con- 

 sists in re-heating the hardened steel to a temperature far 

 short of that to which it was raised before hardening : this 

 heating may or may not be followed by rapid cooling. 

 Annealing consists in heating the mass to a temperature 

 higher than that used for tempering, and allowing it to 

 cool slowly. 



First, let the prominent facts be demonstrated experi- 

 mentally. 



[Three sword-blades of identical quality, made by an 

 eminent sword- smith, Mr. Wilkinson, were taken. It 

 was shown by bending one that it was soft ; this was 

 heated to redness and plunged into cold water, when it 

 became so hard that it broke on the attempt to bend it. 

 Another was bent into a bow, the arc of which was four 

 inches shorter than the sword itself, a common test for 

 " temper," and it sprang back to a straight line when the 

 bending force was removed ; this had been tempered. A 

 third, which had been softened by being cooled slowly, 

 bent easily and remained distorted ] 



The metal has been singularly altered in its properties 

 by comparatively simple treatment, and all these changes 

 it must be remembered have been produced in a solid 

 metal to which nothing has been added, and from which 

 nothing material has been taken. The theory of this 

 operation which I have just conducted has been 

 laboriously built up, and its consideration introduces 

 many questions of great interest both in the history of 

 science, and in our knowledge of molecular physics. 

 First as regards the history of the subject. The know- 

 ledge that steel might be hardened must have come to us 

 from remote antiquity. Copper hardened with tin was its 

 only predecessor, and it continued to be used very long 

 after it was known that steel might be hardened. It 

 would, moreover, appear that a desire to appreciate the 

 difficulties of a people to whom cutting instruments of 

 hard steel were unknown, seems to have induced 

 experimenters in quite recent times to fashion imple- 

 ments of bronze, and a trustworthy authority tells us that 

 " Sir Francis Chantry formed an alloy containing about 

 16 parts of copper, i\ of zinc, and ■i\ of tin, of which 

 he had a razor made, and I believe even shaved with it.' ^ 

 The Greek alchemical manuscripts which have been so 

 carefully examined by M. Berthelot give various receipts 

 from which it is evident that in the early days the nature 

 of the quenching fluid was considered to be all-important. 

 There were certain rivers the waters of which were 

 supposed to be specially efficacious. Pliny, who says 

 that the difference between waters of various rivers can 

 be recognized by workers in steel, also knew that oil might 

 be used with advantage for hardening certain varieties 

 of the metal. It is sad to think how many of the old 

 receipts for hardening and tempering have been lost. 

 What would we not give, for instance, for the records of 

 the Gallic prototype of our Iron and Steel Institute, the 

 " Collegium Fabrorum Ferrariorum^'^di guild with similar 

 aims, formed in the time of the Roman Republic, for the 

 advancement of knowledge, for the good of the State, and 

 not for that of its individual members ? The belief, how- 

 ever, in the efficacy of curious nostrums and solutions for 

 hardening steel could hardly have been firmer at any 

 period than in the sixteenth century of our era, Shake- 



' King Henry IV , Part II., Act iv., Scene 3. 



^ " Engines of War," by H. Wilkinson, p. 194 (1841). 



3 " La Ferronnerie," par F. Liger, t. ii. p. 147 (Paris, 1875). 



speare suggests that Othello's sword " of Spain " had been 

 hardened in a cold stream for he says it had 

 " the ice brook's temper " ; 



but cold water "was far too simple a material for many a 

 sixteenth century artificer to employ, as is shown by the 

 quaint recipes contained in one of the earliest books 

 of trade secrets, which, by its title, showed the existence 

 of the belief that the " right use of alchemy " was to bring 

 chemical knowledge to bear upon industry. The earliest 

 edition was published in 1531,^ and the first EngHsh 

 translation^ in 1583, from which the following extracts 

 may be of interest. " Take snayles, and first drawne water 

 of a red die of which water being taken in the two firste 

 moneths of haruest when it raynes," boil it with the 

 snails, " then heate your iron red bote and quench it therein 

 and it shall be hard as Steele." " Ye may do the like with 

 the blood of a man of xxx yeres of age, and of sanguine 

 complexion, being of a merry nature and pleasaunt .... 

 distilled in the middst of May." This may seem trivial 

 enough, but the belief in the efficacy of such solutions 

 survived into the present century, for I find in a work 

 published in 18 10 that the artist is prettily directed^ " to 

 take the root of blue lilies, infuse it in wine and quench 

 the steel in it," and the steel will be hard ; on the other 

 hand, he is told that if he " takes the juice or water of 

 common beans and quenches iron or steel in it, it will be 

 soft as lead." I am at a loss to explain the confusion 

 which has arisen from this source. As must always be 

 the case when the practice of an art is purely empirical, 

 such procedure was often fantastic, but it is by no means 

 obsolete, for probably at the present day there is hardly a 

 workshop in which some artificer could not be found with 

 a claim to possess a quaint nostrum for hardening steel. 

 Even the use of absurdly compounded baths, to which I 

 have referred, was supported by theoretical views. Otto 

 Tachen,"* for instance, writing of steel in about the year 

 1666, says that steel when it is "quenched in water 

 acquires strength because the light alcaly in the water is 

 a true comforter of the light acid in the iron, and cutlers 

 do strengthen it with the alcaly of animals," hence the 

 use of snails. Again, Lemery •'' explains in much the same 

 way the production of steel by heating iron in the presence 

 of horns of animals. 



I have dwelt so long on these points in order to bring 

 out clearly the fact that the early workers attached great 

 importance to the nature of the fluid in which hot steel 

 was quenched, and they were right, though their theories 

 may have been wrong. The degree of rapidity with 

 which heat is abstracted from the steel during the opera- 

 tion of hardening is as important at the present day as it 

 ever was. Roughly speaking, if steel has to be made 

 glass-hard, ice-cold water, brine, or mercury, is used ; if it 

 has only to be made slightly hard, hot water or oil may be 

 employed ; while, as Thomas Gill ^ suggested in 1818, 

 both " hardening " and " tempering " may be united in a 

 single operation by plunging the hot metal in a bath of 

 molten lead or other suitable metal, which will of course 

 abstract the heat more slowly. 



We must now trace the development of theories relating 

 to the internal constitution of steel. The advent of the 

 phlogistic school with the teaching of Becher and Stahl 

 led to the view that iron gained phlogiston during its con- 

 version into steel. By phlogiston we know that the early 

 chemists really meant energy, but to them phlogiston was 

 represented to be a kind of soul possessed by all metals, 



' "Rechter Gebrauch d. Alchimei," 1531. There were many English 

 editions. 



^ " A profitable boke declaring dyuers approoued remedies," &c. (London, 

 1583). See Prof. Ferguson's learned paper "On some Early Treatises on 

 Techno'ogical Chemistry," Phil. Soc, Glasgow, January 1886. 



3 " The Laboratory or School of Arts," 6th edition, 1799, p. 228. There 

 is a later edition of 1810. 



4 " His Key to the Ancient Hippocratical Learning," p. 68 (London, 

 1690). 



5 " A Course of Chemistry," ind edition, 168'i, p. 131. 



6 Thomson's Annals of Philo ophy, xii., i8i8, p. 58. 



