LIQUID AIR. 



41 



vacuum to vaporize the liquid rapidly. The most common form of 

 these vessels is that of a globe. Such a vessel is known as a Dewar 

 globe or bulb. 



It has been found that liquid air can be kept very well by putting 

 it in a tin or galvanized iron vessel, which in turn is placed in a 

 larger one, and then filling the space between the two with felt. 

 Under these conditions vaporization takes place quite slowly, and 

 it is possible to transport the liquid comparatively long distances. It 

 has, for example, been transported from New York to Baltimore and 

 Washington. In one case with Avhich the writer is familiar two 

 cans were taken from Mr. Tripler's laboratory in the morning, de- 

 livered at the Johns Hopkins University in the afternoon, and used 

 to illustrate a lecture in the evening. After the lecture there was 

 enough left for certain experiments that were carried on during the 

 rest of the night. 



Tripler, Linde, and Hampson have all succeeded in devising forms 

 of apparatus by means of which air can be liquefied without the aid 

 of other cooling agents than the expanding air. In prin- 

 ciple the methods employed by these three workers are essen- 

 tially the same. It appears from the published statements 

 that at the present time Tripler's plant is the most efiicient. 

 While a few years ago a half pint or so of liquid air is said 

 to have cost five hundred dollars, now five gallons can be 

 made for about twenty dollars, and probably much less. The 

 general working of Tripler's apparatus can be made clear by 

 the aid of the accompanying drawing, Fig. 2. A^, A^, A^ 

 represent steam compression pumps. Air is taken through I 

 from above the roof of the laboratory. In the first pump it 

 is compressed to sixty-five pounds to the square inch. It, of 



Fic. 2. — Diagram showing Wokkino of Comprkssion Apparatus for making Liquid Air. 



course, becomes heated as it is compressed. In order to cool it down 

 again it is passed through a coil, B^, which is surrounded by water of 

 the ordinary temperature. This compressed and cooled air is then fur- 

 ther compressed in the second pump, A^, to four hundred pounds to the 



FOL. LT.— 4 



