LIQUID AIR. 43 



oxygen, and after a time the liquid that is left is much richer in 

 oxygen than ordinary air. When liquid air is poured upon water 

 it, being a little lighter than the water, floats, not quietly, to be sure, 

 but in a very troubled way. Soon, however, the liquid sinks to the 

 bottom because the nitrogen, which is the lighter constituent, passes 

 into the gaseous state, and the liquid oxygen which is left is a little 

 heavier than water. The experiment is a very beautiful one. A 

 scientific poet could alone do justice to it. The beauty is enhanced 

 by the fact that while liquid air is colorless, or practically so, liquid 

 oxygen is distinctly blue. 



Although liquid air has the temperature —191° C. ( -312° F.), 

 one can without danger pass the hand through it rapidly. The sen- 

 sation is a new one, but it is evanescent. Very serious results would 

 follow if the hand were allowed to remain in the liquid even for a 

 short time. The tissues would be killed. So also, it is possible to 

 pass the hand rapidly through molten lead without injury. In the 

 latter case the moisture on the hand is converted into vapor which 

 forms a protecting cushion between the hand and the hot liquid; 

 while, in the former case, the heat of the hand converts the liquid air 

 immediately surrounding it into gas which prevents the liquid from 

 coming in contact with the hand. 



"When the liquid is poured out of a vessel in the air it is rapidly 

 converted into gas. The great lowering in the temperature causes 

 a condensation of the moisture of the air in the form of a cloud. 

 The same thing is seen when the cover is removed from a can 

 containing the liquid. Of course, this liquid does not wet things 

 as water does. When, however, as happened in ISTew York, the lec- 

 turer deliberately pours a dipperful of the liquid upon a priceless 

 Worth gown, he may expect to hear expressions of horror from the 

 owner. This experiment passed off most successfully. Every trace 

 of the liquid air was converted into invisible gases before the fleet- 

 ing agony of the sympathetic audience had passed away. 



The effects of very low temperature upon a number of substances 

 have been studied, and some of them can easily be shown. Paraffin, 

 resin, and rubber immersed in liquid air soon become very brittle, 

 and. the color of the resin is completely changed. A beefsteak 

 or an onion also becomes brittle, and can be broken into small frag- 

 ments by the blow of a hammer. A similar effect is produced in 

 the case of some metals. Tin and iron, for example, become brittle, 

 and the tenacity of the iron is greatly increased. A copper wire, 

 however, retains its flexibility. At low temperatures the electric 

 conductivity of all metals is increased. In general, the lower the 

 temperature the greater the conductivity. If a copper wire could 

 by any means be kept cold enough, electrical energy could be trans- 



