Paraffin Baths for Vacuum Embedding. By J. F. Gemmill. 27 



supply a suitable base for the bell-jar, and to put the jar so fitted 

 into the inside of the bath, leading a tube to it from the aspirator 

 in whatever way is most convenient. For example, a small piece 

 of suitable piping can be soldered through one side and left as a 

 permanent fixture, to which tubing may be attached, leading on 

 the one hand to the aspirator, and on the other with the bell-jar 

 inside. Or, as most baths have an opening in the roof for letting 

 down a thermometer, this opening may be utilized for the passage 

 of the tube. The base may be of strong copper, or, perhaps, better 

 of plate glass, the thickness being greater the larger the bell-jar 

 used. 



— D 



Fig. 3. 



The dishes containing melted paraffin and the objects to be 

 embedded are placed under the bell-jar. The latter is then fitted 

 on to the base with the help of the rubber ring, and exhaustion is 

 effected as before. Or again, as in the case of the open bath, the 

 process may be carried on by using tubes with suitable stoppers. 



It is well to have the top of the bell-jar fitted with stopcocks, 

 as shown in the sketch. The lower of the stopcocks enables one 

 to shut off the vacuum chamber at once when the required degree 

 of diminished pressure has been attained. The upper of the stop- 

 cocks is useful when the process is at an end, as when opened it 

 allows free entrance of air into the bell-jar without the least risk 

 that any water may be sucked in from the tubing connected with 

 the aspirator. 



