ATTAINMENT OF VERY LOW TEMPERATURES. 



of the vacuum-vessel H aud the inner wall of the lower part of the sup- 

 porting tube mm is made. The brass ring o is supported above by a 

 slight flange on the inside of the lower portion of the tube m, and a 

 rubber ring is compressed between this ring and a gland p, which is 

 forced home by means of three screws, of which one is seen in the 

 diagram. As the lower part of the tube m is continuous with the brass 

 plate nn, it never becomes very cold, and the junction is always gas-tight. 

 The liquid hydrogen which is formed in the vacuum vessel H is 

 collected in the vessel K. This vessel is placed inside a tube L, which is 

 long enough to enclose H as far as the lower edge of the brass tube h, 

 which forms part of the gland p. A rubber sleeve is secured by wire to 

 h and L making a gas-tight junction. By opening the tap r gas can 

 be allowed to escape from the space within L, and consequently liquid 

 can flow from H into K. This enables one to dispense with a cock at 

 the bottom of the vacuum vessel //. By connecting the cock r to the 

 supply pipe from the gasometer (fig. 8, S), loss of hydrogen can be 

 avoided. 



During an experiment, the tube L and its contents are enclosed 

 within an arrangement of three concentric glass shades in order to 

 shield ofif heat, and to prevent the condensation of moisture taking 

 place. 



The apparatus is supported on a cast iron stand with a vertical 

 column 130 cm. high, which screws into the bottom of the brass plate 

 nn. This latter is of oval shape and supports 

 a brass case Q which surrounds the upper part 

 of the apparatus, the intermediate space being 

 packed with wool. 



The use of the cocks t, v and w must now 

 be pointed out. With this type of liquefier, the 

 first step toward liquefaction of hydrogen is to 

 cool the whole apparatus to the temperature of 

 liquid air. With this object a small brass tap 

 V (fig. 5) is fitted by means of a rubber cap 

 to the nozzle of the vacuum vessel H and this 

 is in turn connected by a short piece of rubber 

 tube to a glass tube 300 mm. long. By closing 

 the cocks t and w, opening the cock V , and 

 starting the exhaust pump, liquid air can be 

 drawn through the glass tube and the cock V 

 into the vacuum vessel H from a vacuum ves- 

 sel, usually containing two liters of the liquid. 

 Liquid air is drawn into the vessel H till it 

 rises above the top of the coil D; then, by 

 closing the cock V and maintaining the exhaust, the temperature of 



Fig. 5. — Brass tap to 

 vacuum vessel. 



