1888 - 89 .] Mr John Aitken on Bust Particles . 
141 
dirty, the grease sticking to everything with which it comes in con- 
tact, so that I prefer to use the second. 
The plate B is fastened on with the ordinary strong solution of 
indiarubher, which makes an air-tight joint, and is sufficiently strong 
for the purpose, while at the same time the joint can he forced 
when necessary to get access to the interior for cleaning, &c. 
Should this joint leak at any time, all that is necessary is to make 
a stroke of the pump, and rub the place where the fault is with a 
little of the indiarubher solution, which soon closes it. At first 
some difficulty was found in making quite tight the joint where 
the tube D enters the receiver. The leakage was due to imperfec- 
tions on the interior surface of the indiarubher tube, and the joint 
had always to he tied. This difficulty has, however, been overcome 
by improving the inside of the indiarubher tube. To do this the 
tube is drawn over a piece of brass tube slightly larger than itself, 
half an inch or so of it is turned back so as to expose the interior. 
This surface is then carefully rubbed over where defective, with the 
solution of indiarubher, till good contact is made ; a quantity of the 
solution is put on sufficient to fill up all imperfections ; the surface 
of the brass tube is then wetted with water, and the indiarubher 
tube turned to its natural position, and left a day or two to dry. 
By this means all inequalities in the interior of the tube are levelled 
up, and it is always found to make a perfectly tight joint when put 
in its place without being tied. For convenience, the indiarubher 
tube H is cemented to the shoulder piece G on the tube D. 
If this indiarubber joint is objected to, then a metal one held 
close by means of a screw may be used. The joint would require 
to he made quite true and air-tight. If a leather washer is used, 
care must be taken, as any variation in its thickness will alter the 
distance between the stage and the top of the receiver. The 
arrangement sketched has been found to work satisfactorily and 
easily. When the stage is to he taken out, the tube D is simply 
drawn down with a slight twisting movement, and it comes away 
easily ; in putting it in its place, the process is simply reversed, 
twisting till one feels the shoulder is resting against F. But for 
general use, perhaps the screw joint is the best. 
Before taking the stage out, the stopcock T is opened and all the 
water is allowed to run out of the receiver. In withdrawing the 
