596 



Sir James Dewar 



[Jan. 17, 



gas passing out through the coiled copper tube, which warms it to 

 ordinary temperature before issuing at C. One practical form of 

 such an evaporator constructed of metal is shown in Fig. 2. This 

 is a spherical vacuum container made of copper, nickel or brass. 

 The delivery tube S (corresponding to the vacuum sjphon S of 

 Fig. 1) is siiown issuing from the neck under tlie release valve- 

 stopper B (acting in the same way as D in Fig. 1), and passes down 

 to the annular evaporating chamber E. The outlet from this 

 consists of a spiral coil of copper pipe wound round the neck and 

 terminating at the regulating valve V. Diffei-ent forms of containers 

 are represented in Fig. ;-k 



What may be called an emergency form was adapted from an 

 ordinary glass thermos flask. This was suital>le for easy handling in 

 hospital or trench, and is illustrated in Fig. 4:{(f). The neck of the 



Fig. 3 



inner glass flask A is fltted air-tight into the outer metal case by 

 means of rubber washers. The lip of the screwed cap C was also 

 provided with a rubber washer. The delivery tube S was soldered 

 through the top, where also the combined screw stopper and blow-off 

 valve B was fixed. The evaporating chamber E surrounded the 

 lower portion of the outer case, and from this the spiral outlet tube 

 was wound round the vessel above E, up to and ending in the 

 regulating valve V. The deh'very tube S was bent at right angles 

 outside the cap and led down to E by a union N, and a short flexible 

 tube. This allowed the recjuisite play for tightly screwing on the 

 cap. 8uch a vessel provided a steady supply of oxygen of about 

 two litres a minute, sufficient for one person for respiration for over 

 five hours. It weighed less than three kilos, when full and complete 

 in a wicker basket, in which it was fixed for protection. 



