46 POPULAR SCIENCE MONTHLY. 



sideration the question of cost, it may be pointed out that liquid-air 

 engines would have the advantage of compactness, though they would 

 necessarily be heavy, as they would have to be strong enough to stand 

 the great pressure to which they would be subjected. 



The third application of liquid air that has been suggested is 

 in the preparation of an explosive. In fact, an explosive has been 

 made and used for some time in which liquid air is one of the con- 

 stituents. When the liquid from which a part of the nitrogen has 

 boiled off is mixed with powdered charcoal, the mixture burns with 

 great rapidity and great explosive force. " To make this explosive. Dr. 

 Linde pours the liquid containing about forty or fifty per cent of 

 oxygen on fragments of wood charcoal, two or four cubic milli- 

 metres in size. These are kept from scattering under the ebullition 

 of the liquid by mixing them into a sort of sponge with about one 

 third of their weight of cotton wool." Of course, this explosive 

 must be made at or near the place where it is used. It has been in 

 use in the way of a practical test in a coal mine at Pensberg, near 

 Munich. It is claimed that the results were satisfactory. The 

 chief advantage of the explosive is its cheapness, and the fact that 

 it soon loses its power of exploding. 



Finally, the fourth application of liquid air is for the purpose 

 of getting oxygen from the air. This can be accomplished by chemi- 

 cal means, but the chemical method is somewhat expensive. Oxygen 

 hts commercial value, and cheap oxygen would be a decided advan- 

 tage in a number of branches of industry. It will be observed that 

 it is the liquid oxygen that makes possible the preparation of the 

 explosive described in the last paragraph. Oxygen as such in the 

 form of gas is of value in Deacon's process for the manufacture of 

 chlorine. In this process air and hydrochloric acid are caused to 

 act upon each other so as to form water and chlorine. The nitrogen 

 takes no part in the act, and it would be an advantage if it could 

 be left out. It is only the oxygen that is wanted. There are many 

 other possible uses for oxygen either in the liquid or in the gaseous 

 form, but these need no mention here. 



In conclusion it may safely be said that it is highly probable 

 that liquid air will be found to be a useful substance, but it is im- 

 possible at present to speak with any confidence of the particular 

 uses that will be made of it. As work with it is being carried on 

 energetically in at least three countries, we may confidently expect 

 important developments in the near future. 



