170 Dewar — The Nadir of Temperature 



reduced by the Callendar and Dickson methods. The table 

 [here omitted] gives the results for seven thermometers, viz., 

 two of platinum, one of gold, silver, copper, and iron, and one 

 of platinum-rhodium alloy. Of these the lowest boiling point 

 for hydrogen was given by the gold thermometer. Next to it 

 came one of the platinum thermometers, and then silver, while 

 copper and the iron differ from the gold value by 26 and 32 

 degrees respectively. The gold thermometer would make the 

 boiling point 23°*5 instead of the 20 o, 5 given by the gas ther- 

 mometer. Then the reduction of temperature under exhaus- 

 tion amounts to only 1° instead of 4° as given by the gas 

 thermometer. The extraordinary reduction in resistance of 

 some of the metals at the boiling point of hydrogen is very 

 remarkable. Thus copper has only l/105th, gold l/30th, plati- 

 num l/35th to l/17th, silver l/24th the resistance at melting 

 ice, wmereas iron is only reduced to 1/8 th part of the same 

 initial resistance. The real law correlating electric resistance 

 and temperature within the limits we are considering is 

 unknown, and no thermometer of this kind can be relied on for 

 giving accurate temperatures up to and below the boiling point 

 of hydrogen. The curves are discussed in the paper, and I 

 am indebted to Mr. J. H. D. Dickinson and Mr. J. E. Petavel 

 for help in this part of the work. 



Helium separated from the gas of the King's "Well, Bath, 

 and purified by passing through a TJ-tube immersed in liquid 

 hydrogen, was filled directly into the ordinary form of Cailletet 

 gas receiver used with his apparatus, and subjected to a pres- 

 sure of 80 atmospheres, while a portion of the narrow part of 

 the glass tube was immersed in liquid hydrogen. On sudden 

 expansion from this pressure to atmospheric pressure a mist 

 from the production of some solid body was clearly visible. 

 After several compressions and expansions, the end of the 

 tube contained a small amount of a solid body that passed 

 directly into gas when the liquid hydrogen was removed and 

 the tube kept in the vapor of hydrogen above the liquid. 

 On lowering the temperature of the liquid hydrogen by 

 exhaustion to its melting point, which is about 16° absolute, 

 and repeating the expansions on the gas from which the solid 

 had separated by the previous expansions at the boiling point 

 or 20 o, 5, no mist was seen. From this it appears the mist was 

 caused by some other material than helium, in all probability 

 neon, and when the latter is removed no mist is seen, when 

 the gas is expanded from 80 to 100 atmospheres, even although 

 the tube is surrounded with solid hydrogen. From experi- 

 ments made on hydrogen that had been similarly purified like 

 the helium and used in the same apparatus, it appears a mist 

 can be seen in hydrogen (under the same conditions of expan- 

 sion as applied to the helium sample of gas) when the initial 



