SUSPENDED CHANGES IN NATURE 31 



They say that Celtic tin melts much more easily than lead. A proof for the 

 fusibility is that it melts even in water. It is apparently very sensitive to 

 exterior influences. It melts also in the cold, when there is frost. 



The knowledge of the tin disease is no more modern than the knowl- 

 edge of most other diseases. 



In this connection it is interesting to speculate on the antiquity of 

 the use of tin. This metal is one of the easiest to obtain from its ores, 

 and may have been used far earlier in the history of mankind than is 

 generally supposed. Evidence in the form of utensils, etc., would of 

 course have been destroyed by the tin disease. 



We are indebted to the investigations of Professor Cohen for a more 

 striking example of a metastable metal, that of the " explosive " anti- 

 mony. By passing an electric current through a solution of antimony 

 chloride this metal may be deposited on platinum in the form of a thick 

 metallic coating. This electrolytic antimony is in the metastable con- 

 dition exhibiting the same state of passive resistance towards change 

 as the metastable sulphur, sodium acetate and water. If scratched with 

 a file it changes to the stable form of antimony with explosive violence, 

 heat is given off and dense clouds of whitish vapor are evolved. The 

 metal has changed to the ordinary antimony, used so much in manufac- 

 turing as a basis for bearing metals. The method of bringing this 

 change about and the velocity of transformation reminds one forcibly of 

 the transition of undercooled water to the stable form. 



That many other metals have the property of existing in the meta- 

 stable state is highly probable. In this connection the hardening of 

 steel is of especial interest, particularly so since the manufacture of steel 

 has played so important a role in the advance of civilization. The 

 method of tempering steel has been the subject of numerous trade sec- 

 rets. In a book of recipes published in the sixteenth century the reader 

 is told that steel may be hardened by quenching it in rain water in which 

 snails have been boiled ; also that 



Ye may do the like with the blood of a young man XXX years of age, 

 and of a sanguine complection, being of a merry nature and pleasant . . . , 

 distilled in the middst of May. 



Fortunately for this type of young man the modern steel manufac- 

 turer uses other methods for hardening steel. 



The discovery of hardening steel by the quenching process is of 

 course as much of a mystery as the method of raising bread by fermenta- 

 tion, we only know that it is an ancient process and moreover of great 

 interest from the standpoint of delayed transformations. 



If the alloy that we call steel is taken at a high temperature and al- 

 lowed to cool very slowly it becomes soft and tools made from it will not 

 have a cutting edge. Sudden chilling, however, produces in the metal a 

 decided hardness. The results obtained by different rates of cooling have 



