20 Transac/io/is of the Society. 



V . — Adaptation of Ordinary Paraffin Baths for Vacuum 



Embedding. 



By J. F. Gemmill, M.A. D.Sc. M.J). 



(Bead November 10, 1910.) 



The advantages of being able to embed certain objects in a vacuum, 

 or under diminished atmospheric pressure, are well known. Baths 

 made for the purpose are, however, costly, and many workers who 

 possess a good ordinary paraffin bath may welcome a means of 

 adapting it when desired to embedding in vacuo. 



The following arrangement works satisfactorily in the case of ;i 

 large open embedding bath which was made for me eight or nine 

 years ago by the Cambridge Scientific Instrument Co., according 

 to a model slightly modified from that given under No. 291 of 

 their catalogue (fig. 3). A similar arrangement can be adapted to 

 closed baths. 



A. An ordinary small aspirator connected with C, a bell-jar, 

 by means of strong rubber tubing, in the course of which a gauge 

 or indicator (B in the sketch) may, if desired, be interposed. The 

 bell-jar should be small, e.g. 2-3 in. across the mouth. 



D. A flat ring of good rubber, about £ in. in thickness, A in. 

 broad, and of a diameter suited to the size of the bell-jar. 



The jar I use was got by cutting off the bottom of a small 

 bottle of fairly strong glass, grinding the cut end flat, and at the 

 same time very slightly smoothing the edges. 



Bell-jar and rubber ring were made just of the right size to fit 

 over any one of the small embedding pots on the top of the bath. 

 The ring serves as an air-tight joint or washer between the bell-jar 

 and the bath. When the jar is fitted in position and the water 

 turned on, the air pressure within the jar can readily be reduced to 

 as low as ^ in. of mercury. But unless when air has to be 

 extracted from some cavity in the specimen being embedded, I 

 prefer to work with a much more imperfect vacuum, especially in 

 the case of delicate tissues. 



One must remember that only a strongly made open bath could 

 stand having a vacuum chamber fitted on any part of it. Practi- 

 cally all open baths have, however, places for holding embedding 

 tubes. These tubes can be fitted with a suitable stopper and 

 exhausted in the same way as the bell-jar, without risk of break- 

 age of any kind unless they are very thin. 



In the case of closed embedding baths, all one has to do is to 



