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wood it is thoroughly soaked in glycerine'). On this coating rests 
a leather collar b4,, which has been made by pressing it, when 
moist, into a mould made specially for it. When the pressure 
below the leather collar increases, the inner part of this is pressed 
against the steel rod, and hence the higher the pressure the better 
the closure. If however the plunger moves upwards and the vacuum 
occurs in tke compression-tube, which vacuum with closed suction- 
valve can amount to 10 em. of mercury (comp. Pl. IIT), the closure 
would be prevented owing to the pressure from without; therefore 
the leather ring must be pressed artificially against the piston-rod 
(comp. § 2 % 1). For this purpose we have placed in the leather 
collar an india-rubber ring b,,, which presses the collar against the 
plunger, when the packing-ring is tightened. 
The packing-compressor by, with the lining bz» is pressed down 
by the nut bj, screwed on to the forcing-cylinder. In this nut also 
a wooden lining &3; is screwed, through which the plunger runs. 
In order to keep the packing entirely under the glycerine (comp. 
§ 2 U 1) a small cup bie is placed on the nut 2, which is entirely 
filled with glycerine and which communicates by two tubes d:3 and 
and bj, and grooves bz, in the nut with the space between the nut 
and the cylinder bj; and also with the space between the packing- 
compressor and the plunger. The air in this space can escape 
through the longer tube while the space is being filled by the 
glycerine through the other tube. 
The screw-threads bi; between the eylinder-wall C, and the nut bj 
are filled with wax in order to prevent the glycerine from leaking 
away along them. 
If ‘the apparatus is out of use for some time, the glycerine is 
removed to prevent it from attracting water and hence causing rust, 
while the wooden linings are kept in glycerine. 
In screwing off the nut the glycerine which flows out is caught 
in the cup Vio, fitting on the support Vj). The glycerine is removed 
from the compression cylinder by means of a pipette and blotting 
paper. The mercury (7 KG.) is left in the pump. 
For the preparation of the apparatus exactly measured quantities 
of glycerine are poured into the forcing cylinder (70 c.c.) and into 
the cup bjz- 
To introduce the glycerine into the closed pump the packing is 
1) It is first immersed in glycerine and turned nearly to its proper dimensions, it 
is again soaked for some time in glycerine and then turned to its correct size, 
Reserve pieces are kept in stock, 
a 
