4 0-2 



Prof. H. E. Armstrong on Low-Temperature Resaarch 



The final conclusion deducible from the investigation carried out in 

 <;onjunction with Professor Fleming was announced as being that 

 " at the zero of absolute temperature all pure metals would be per- 

 fect conductors of electricity." A full account of this work was given 

 by Professor Fleming on Friday, June 5, 1896. This was the first 

 occasion on which the extraordinary change in properties conditioned 

 by cooling to a very low temperature was brought home to an audience. 



Liquid oxysren was shown to be nearly as transparent to high- 

 temperature radiations as chloroform, one of the most transparent 

 liquids next t'o carbon bisulphide. The advantage of a coating of 

 mercury on the interior surface of the vacuum vessel as a means of 

 preventing the access of heat from without to the cooled liquid within 

 was commented upon. Then illustrations were given of the behaviour 

 of a small residue of mercury vapour within exhausted vessels. 

 Attention was called to the alteration in appearance of many coloured 

 substances — mercury, uranium and platinum compounds — when 

 cooled in liquid air. The change of indiarubber from the plastic 

 condition into that of a glass-brittle substance was demonstrated for 

 the first time. Attention was drawn to the possibility of dividing 

 organic substances which solidify only at very low temperatures into 

 two classes — those which crystallize and those which form glasses. Bi- 

 sulphide of carbon belongs to the former, ordinary alcohol to the latter. 



A method of determining latent and specific heats at low tem- 

 peratures with the aid of the actual apparatus used was then demon- 

 strated. The method involved the collection of the gas volatilized by 

 the heat extracted from a substance when dropped into liquid oxygen. 



The effect of very low temperatures in increasing cohesion in 

 metals was then demonstrated and an account given of experiments 

 to determine the breaking strain of metals cooled to - 180°. A spiral 

 spring made of fusible metal, which is quickly drawn out into a 

 straight wire at ordinary temperatures by an ounce weight, will 

 support a couple of pounds at - 182° and vibrate like a steel spring. 

 The following table illustrates the character of the increase in cohesive 

 strength metals undergo when cooled : 



