Magnetization and Magnetic Change of Length. 

 Table VII. 



509 



Alloys. 



28-32 % Ni. 



26-64 % Ni. ; 24-40 % Ni. 



24-04 %Ni. 



Before cooling ... 



8-15 



846 813 



8-06 



After cooling ... 



8-01 



7-99 8-06 



7-94 



Thus the density is diminished by cooling them in liquid 

 air ; M. Ch. Ed. Griiillaume* specially investigated this point 

 by measuring the coefficient of thermal expansion at low- 

 temperatures 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. 



II. Second Sekies. 



To obtain a constant low temperature lying between the 

 ordinary temperature and that of liquid air, a method of slow 

 cooling was applied. The specimen-holder in the former 

 apparatus was covered with a water-tight brass cylinder, 

 and a suitable amount of liquid air was poured into the 

 interspace between the cylinder and the Dewar tube. The 

 temperatures above — 15° 0. were, however, obtained by 

 dipping the specimen directly into a freezing-mixture (snow 

 and common salt) contained in the Dewar tube. The experi- 

 ment was commenced with the specimen in the annealed 

 state, and measurements were made at successively decreas- 

 ing temperatures. During one set of observations, which 

 usually required 7 or 8 minutes, the temperature was fairly 

 constant and its change did not exceed one degree in the 

 most unfavourable case. Since the cooling was very slow 

 and the specimen was doubly enclosed in copper and brass 

 tubes, the temperature of the specimen may be regarded as 

 constant throughout its entire length. 



The temperature of the specimen was measured by a thermo- 

 electric couple of platinum and german-silver. The wires were 

 insulated with a thin caoutchouc tube. One of the junctions 

 was brought in contact with the specimen at its middle, while 

 the other was insulated with asbestos papers and inserted in a 

 copper tube. The tube was dipped into the water-bath, and its 

 temperature was observed with a thermometer placed in the 

 bath. The thermoelectric current w r as measured with a low 



* Guillaume, Bulletin de la Sociite d' Encouragement, Mars 1898, p. 273, 



