1894.] on Scientific Uses of Liquid Air. 401 



of strength is solely due to the low temperature, and persists only 

 during its continuance. Wires that have been cooled to the tempera- 

 ture of — 182° C. and allowed to regain the ordinary temperature, 

 are in no way changed as regards their breaking stress. 



A second series of experiments were made with a set of cast test 

 pieces of metals and alloys. The test pieces, all cast in the same 

 mould, were 2 inches long with J inch spherical ends, the cylindrical 

 portion being T 2 ^ inch diameter. The spherical ends of the test 

 pieces rested in similar cavities made in a special set of steel supports 

 that fitted on to the testing machine. Crystalline metals give castings 

 that are far from uniform one with another, and it is very difficult 

 to get even comparable results with metals like zinc, bismuth and 

 antimony. The following table gives the experimental results : — 



Table II. — Breaking Stress in Pounds of Cast Metallic Test Pieces. 

 Diameter op Kod 0*2 Inch. 



15° C. — 182° C. I 15° C. — 182° C. 



Tin .. .. 200 390 Bismuth 60 30 



Lead .. .. 77 170 Antimony .... 61 30 



Zinc .... 35 26 Solder 300 645 



Mercury .. 31 [ Fusible metal (Woods) 140 450 



It w T ill be noted that in this list the breaking stress, by cooling 

 to — 182° C, has been increased to three times its usual value in the 

 case of fusible metal, and to twice its usual value in the case of tin, 

 lead and solder. The results w r ith zinc, bismuth and antimony are 

 exceptional, seeing they appear to be diminished in tenacity. This, 

 however, may be only apparent, because the stresses set up in cooling 

 such highly crystalline bodies probably weaken some set of cleavage 

 planes so that rupture is then comparatively easy. In any case it must 

 be admitted that no reliance can be placed on the tenacity of highly 

 crystalline metals. The breaking stress of mercury is interesting, and 

 turns out to be at — 182° C. nearly half that of lead at the ordinary 

 temperatures. The percentage elongation is not given in the foregoing 

 tables, simply because the value of such measurements is of little 

 importance when such short pieces of the metals are under observa- 

 tion. The general results of such observations are, however, inter- 

 esting : thus, lead and tin at ordinary temperatures elongate before 

 breaking about the same amount, whereas if tin is cooled to — 182° C. 

 it hardly shows any extension, and lead under such conditions shows 

 no change, stretching as much at —182° as at 15° C. Solder and 

 fusible metal stretch less, and the cross section of the break is much 

 less at — 182° than at 15° C. The above experiments can only be 

 considered as preliminary to a more elaborate investigation of the 

 actual variation of the elastic constants at low temparatures. It will 

 require complex experimental arrangements to get reliable measure- 

 ments of the Young modulus and the rigidity modulus at the tem- 

 perature of boiling liquid air. In the ca?e of fusible metal, a first 

 attempt to compare the ratio of the Young modulus at 15° and 



Vol. XIV. (No. 88.) 2 e 



