2b Mr /. Brown on 



the liquid. On a former occasion when sending me a supply 

 for use in my own laboratory, Mr. Moss expressed a doubt if 

 the Dublin atmosphere would suit Belfast, but on this occasion 

 he expressed the conviction that an abundant supply of some 

 cooling medium will not be out of place on Guy Fawkes Day 

 in the North. May I assure Mr. Moss, on your authority, that 

 it is not by any means out of place, and that we tender our 

 warmest thanks for this coldest of gifts ? 



Liquid air is a clear, transparent fluid. The boiling point is 

 about i90°to 2oo° under atmospheric pressure. The experi- 

 ments that can be performed with liquid air depend chiefly on 

 the effects produced by this very low temperature. Poured 

 upon water, liquid air floats, forming a cup of ice, in which it 

 boils. Immersed in liquid air, mercury may be frozen, and 

 forms a mercury casting, which can be forged cold into a hook, 

 on which we may suspend a weight, till the warmth of the 

 surrounding atmosphere melts it into liquid drops, when the 

 weight of course fails. Alcohol may be frozen, ice hardened 

 till it is said to cut glass, and indiarubber becomes brittle like a 

 pipe stem. Sulphur, vermilion, and a solution of cobalt 

 chloride in alcohol lose their colours. The electric resistance 

 of metals is decreased manifold. Owing to the fact that the 

 nitrogen in air is more volatile than the oxygen, it evaporates 

 first, and in liquid air which has been standing some time the 

 residue is chiefly oxygen. On this account a process of obtain- 

 ing oxygen sufficiently pure for many purposes has been pro- 

 posed. To illustrate this a shaving splinter of wood burns up 

 brightly over such stale liquid air. Felt or cotton wool soaked 

 in the liquid burns with explosive violence. A jet of hydrogen 

 will burn under the surface of liquid oxygen. Liquid air has 

 been proposed as a carrier of power by using it to drive motors 

 of the steam engine type. Here is an illustration where a tube 

 of liquid air enclosed in an appropriate closed vessel gives off 

 air at sufficient pressure to drive the model engine, and on the 

 screen is a slide of a motor so driven. Here however con- 

 venient in some respects the process might be, the question of 



