44 POPULAR SCIENCE MONTHLY. 



mitted by it with but little loss perhaps none. Mercury is easily 

 frozen by surrounding it with liquid air, and the solid thus formed 

 is very hard, though if it is cooled down sufficiently it becomes 

 brittle. 



Alcohol can be frozen without difficulty by means of liquid air. 

 By the aid of the lowest temperatures hitherto attainable it has 

 only been possible to convert alcohol into a pasty mass. The frozen 

 alcohol is as hard as ice. When alcohol is dropped into liquid air 

 the drops retain the globular form. When taken out on a platinum 

 loop the flame of a Bunsen burner does not set fire to it. 



Phosphorescence is greatly increased by cooling substances down 

 to the temperature of liquid air. This has been shown by means 

 of water, milk, paper, eggs, and feathers. An egg and a feather 

 could be distinctly seen in a dark room. 



Scarlet iodide of mercury is converted into the yellow variety 

 when it is subjected to the temperature of liquid air. Some other 

 colors are changed under the same circumstances, but not enough is 

 known of this subject to warrant a general statement. 



Attention has already been called to the fact that liquid air loses 

 its nitrogen more rapidly than it does its oxygen, and that, after 

 a time, the residue contains a large proportion of oxygen. As com- 

 bustion is combination with oxygen, combustion or burning takes 

 place more readily in contact with this liquid oxygen than it does 

 in the air. If a lighted match is attached to the end of a steel 

 watch spring, and this then plunged beneath the surface of liquid 

 air, the spring will soon take fire and burn brilliantly, the sparks 

 flying off for some distance in beautiful coruscations. Hair felt, 

 which does not burn in the air, burns in a flash when soaked with 

 liquid air. Finally, when liquid air is confined in any vessel not 

 capable of sustaining an enormous pressure, say about ten thousand 

 pounds to the square inch, the vaporization goes on until the vessel 

 bursts or the stopper is forced out. It might therefore be used as 

 an explosive without any addition, but its manipulation is not alto- 

 gether simple. 



Now for the inevitable question : Of what use is liquid air likely 

 to be? This is a perfectly proper question, and yet, if scientific 

 workers always stopped to ask it, and would not work unless they 

 could find a favorable answer, progress would, to say the least, be 

 much slower than it is. Most great practical discoveries have neces- 

 sarily passed through the plaything stage. Some of the most im- 

 portant discoveries have not even furnished playthings, and have 

 found no practical applications as this expression is commonly under- 

 stood. But the production of liquid air, while furnishing mankind 

 with a beautiful and instructive plaything, seems likely to find prac- 



