Critical Phenomena oj Ether. 797 



A. Preparation of the Tubes. 



The tubes employed were of: the design shown in figure 2. 

 The Natterer tube AD is of Jena glass tubing about 1 mm. 

 ■^ 9 in thickness, about 8 or 10 mm. in internal diameter, 

 and from 13 to 16 cm. in length. Inside AD slides 

 freely a piece of Jena-glass tubing C about 3 cm. in 

 length, which is closed at the upper end and thus 

 forms a bell. The bell-tube is fused to a similar 

 piece of tubing B in which are hermetically sealed 

 some tightly packed iron filings ; by means of a 

 sufficiently powerful electromagnet, C and B maybe 

 raised at will. The ether is introduced through the 

 constricted end D which is afterwards sealed off. 



The special purpose of this design is explained 

 later, but, as has already been stated, the bell proved 

 to be a very efficient detector of gaseous impurities. 

 If such impurity is present, it is to be found chiefly 

 in the vapour. By inverting the tube and then 

 slowly bringing it back to the position shown in 

 fig. 2, the bell- tube may be made to fall into the 

 liquid, carrying within it a portion of the vapour. 

 If the vapour is pure it readily condenses, but if it 

 is mixed with gas a bubble remains which dissolves 

 very slowly, since it is subjected to a pressure of 

 only a few centimetres of liquid ether. As a further 

 test, C may be filled by ebullition. If the end D is 

 gently heated, the ether boils briskly, whilst reflux 

 condensation occurs at end A. By this means the 

 gaseous impurity, if present, is brought mainly to 

 the top of the tube, and C is filled with compa- 

 ratively pure vapour from beneath. This sample of 

 vapour may then be compared with that previously 

 obtained. 



In filling the earlier tubes various methods of 

 removing the air were tried. In some cases, a large 

 excess of ether was introduced and the surplus was 

 pumped off with a Topler pump. In other cases, 

 the method described by Travers and Usher (7) was 

 adopted : the ether was frozen with liquid air whilst the tube 

 was exhausted, and the excess of ether was then pumped off 

 before sealing the tube with the blowpipe. In all cases, 

 however, very distinct traces of gaseous impurity were ob- 

 servable : the vapour brought down from end A was far more 

 persistent than that produced in the bell-tube by ebullition, 

 and in order to secure its condensation it was necessary to 



