64 PHYSICAL SCIENCE 



greatly affected at these temperatures. In many 

 cases, where the reaction proceeds rapidly at 

 ordinary temperatures, the rate is reduced to such 

 an extent that in liquid air it becomes too small 

 to be observed. In other cases action may cease 

 altogether, and reagents which would otherwise 

 undergo chemical chancre are maintained in false 

 equilibrium by chemical forces analogous to those 

 of friction. Fluorine, for instance, which attacks 

 glass violently at ordinary temperatures, has no 

 effect on it when cooled to — i8o° C. 



It is found that the elasticity of materials is 

 greatly affected by these low temperatures. On 

 the one hand, iron, lead, and tin, as well as ivory, 

 showed a considerable increase in this property, 

 balls of these substances rebounding to a much 

 greater height than usual. On the other hand, 

 a ball of india-rubber became brittle, and was 

 broken by the fall. Connected with the increase 

 in the elasticity of metals is their increased 

 strength ; wires, for example, will stand a much 

 greater load without pulling out or breaking. 



Low temperatures also affect the magnetic 

 properties of iron, cobalt, and other metals, 

 which are usually magnetic at ordinary tempera- 

 tures, generally increasing the magnetic moment. 

 Oxygen, slightly magnetic as a gas, as a liquid 

 becomes strongly magnetic. The alteration of 

 magnetic properties with temperature has been 

 studied in detail for many years where high 

 temperatures are concerned, and this extension of 

 the research has been of great interest. 



Of even more theoretical importance are the 

 experiments of Onnes on the electrical conduc- 

 tivities of metals at the very low temperatures 



