EXPERIMENTAL METHODS AND APPARATUS. 



29 



leather washers, however, seemed to be the most satisfactory. Steel cap-, 

 EEE serve to tighten the plungers. MM are receptacles for thermometers 

 for measuring the temperature. C is an iron air-bath and protects the cell 

 from rapid changes in temperature. 



In heating a cell of this kind it was found that the rise in temperature should 

 be very gradual. Very great difficulty was encountered in gel ting the ends to 

 hold liquid tight. The screw ends were tightened gradually for several days 

 and for several heatings. On one occasion, when the tube was filled with one 

 of the higher alcohols, a very effective closing was made. It is possible that 

 dried films of oils (like linseed oil) might be of use as washers. 



Fig. 4. 



In beginning the work no serious trouble from the formation of precipi- 

 tates was anticipated. This interference was encountered and a new form of 

 cell is being made which it is hoped will overcome some of the imperfections of 

 the form above described. In this form (fig. 4) the quartz ends are fastened in 

 the ends E' in the same way as in fig. 3. Instead of the plunger P having guide 

 pins it has guide grooves. Part of the plunger has screw threads, by means of 

 which it can be taken out. The whole cap can be removed from the tube T by 

 unscrewing E' , during which the quartz end is untouched. When the ends are 

 removed the quartz window can easily be cleaned. Gold washers are required 

 here between T and E' and between E' and U. 



The remaining parts of fig. 4 represent a diagrammatic arrangement of 

 the apparatus. Only the cell is drawn to scale. The cell was kept in a hori- 

 zontal position so that all bubbles that form would rise in the side tube. As 



