484 Professor H. C. H. Carpenter [March 7, 



deterioration of the tool sets in ; its hardness gradually diminishes, 

 and 2J(iri passu, wear of the tool itself by abrasion occurs. Eventually 

 a stage is" reached at which the cutting operation has to be discon- 

 tinued, and the tool requires re-hardening or re-grinding. The 

 carbon tool of which I have just spoken cannot be used for taking 

 the heavy cuts of which the modern alloy tools are capable, but they 

 retain their pre-eminence even to-day in all machinery work where 

 the highest degree of accuracy attainable is desired. 



A complete theory of the action of such tools must account for 

 both the hardening and toughening of the steel, and its gradual loss 

 of these properties, by the operations I have described. 



Before attempting this, however, it may be interesting to refer 

 briefly to the methods of hardening which chiefly occupied the 

 attention of early workers. 



The Greek alchemical manuscripts give various recipes, from 

 which it is clear that in the early days the nature of the quenching 

 liquid was considered to be all-important. There were certain rivers 

 the waters of which were supposed to be specially efficacious, and 

 Pliny mentions that the difference between waters of various rivers 

 can be recognized by workers in steel. Many old recipes for harden- 

 ing and tempering have been lost, but a number of them have come 

 down through the ages, and from them I take the following 

 illustrations. The first is from a work entitled " Kechtegebrauch & 

 Alchimei," 1531, of which an English translation appeared in 1583. 

 " Take snayles and first-drawn water of a red die, of which water, 

 being taken in the first two monthes of harvest when it raynes, boil it 

 with the snayles, then heate your iron red hot and quench it therein, 

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

 blood of a man of XXX years of age and of a sanguine complexion, 

 being of a merry nature and pleasant, . . . distilled in the middst 

 of May." It would be interesting to know the circumstances which 

 led to this particular experiment being first tried. These instructions 

 may seem trivial, but a belief in the efficacy of such solutions has 

 continued, for in a work published in 1810"' the artist is directed to 

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

 it, 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. When the practice of an art is purely 

 empirical it is liable to take fantastic forms; even at the present 

 day, however, there are many workshops where steel is hardened in 

 which some quaint nostrum still holds sway. Occasionally, but not 

 often, the use of these compounded baths was supported by theoretical 

 views. Otto Tachen, for instance, writing of steel 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 



* *' The Laboratory or School of Arts." 



