30 



ART. 6. K. HONDA AND S. SHIMIZü. 



steels, once cooled in liquid air, is always greater than that 

 before cooling. With 26.64^ and 24.40?ö alloys, the elongation 

 is even increased, by heating it to the ordinary temperature. 



259^ nickel steel does not sensibly elongate at ordinary tem- 

 perature nor in liquid air. 



(g) Change of Density by Cooling. 



The density of the irreversible nickel steels at ordinary tem- 

 perature suffered a permanent change, if they were once dipped in 

 liquid air. This singular fiict was first observed by Hopkinson*. 

 The following table contains the observed values of density : — 



TABLE VII. 



Thus the density is diminished, by cooling them in liquid 

 air ; M. Ch. Ed. Guillaume'I* specially investigated this point, 

 by measuring the coefficient of thermal expansion at low tem- 

 peratures. He found that the irreversible nickel steels expand 

 on being cooled in solid carbon dioxide and again expand when 

 heated to ordinary temperatures. Hence the effect of cooling is 

 to doubly diminish the density of the alloys. 



*) Hopkinson's Original Papers Vol. 11, p. 240. 



t) Guillaume, Bulletin de la Scciété d'Encouragement, mars 1898, p. 273. 



