( 452 J 
The flange Aj (see Pl. III and Pl. V fig. 3) is fastened to 
the bent tube A, of the main conduit by marine-glue, it is closed 
by means of the packing /,., which is screwed on to the overflow 
vessel 4, by means of the nut #3. The contact Zg which inmedia- 
tely gives warning when mercury passes over into this vessel, is 
constructed like C's (see Pl. V fig. 2). The joint 4, on which the 
outlet tube 4, fits with a nut and packing, is forged on to the side 
of the steel vessel %jz which is fastened to the frame (see Pl. II 
‘fig. 2 en 1). 
The steel high-pressure point-cock 49, (see Pl. III) which closes 
the forcing side of the pump is constructed in the manner explained 
in detail for <7; and #%, like #, it is fastened to the trame. The bent 
tube /o) which is more especially intended to enable the pressure in 
the head to be read on the manometer is provided with a (smaller) 
overflow vessel 4; its bottom can be screwed off, but as we need 
hardly fear any mercury on this side, no connections to an electric 
bell were made. From this vessel (not shown on Pl. II as it is not 
fastened to the pump itself) the pressure is brought to the bronze 
high-pressure point-cock lo on the cock-board and can be transferred 
to the manometer Ng, along /s. 
The steel filter-box A3 Pl. III, whither the gas passes from the 
overflow-vessel, consists (P]. V fig. 4) of a hollow cylinder fs), on 
the joints of which the overpipes of the inlets and outlets 43, can 
be connected by nuts. The overpipes are bored trumpetshape on 
the side turned towards the filter box. This contains, enclosed by 
rirgs and perforated supporting plates 433, thicker brass-wires packed 
closely together 434, secondly thinner brass-wires in &,,,, and finally 
between two plates with fine sieve-holes, gold-leaf 4,,, is placed in 
order to remove the last traces of the mercury (comp. § 2 $. 3). 
This filter-box is fastened to the frame of the pump (sce Pl. II, 
fig. 2 and 1). The cocks, tubes or apparatus in which the gas is 
admitted after having traversed this filter need not be made exclus- 
ively of steel or other material, unattacked by mercury, nor need 
all soldering work be avoided, as was the case with the preceding. 
But then they must be placed at such a distance from the pump 
itself, that no contact with mercury is to be feared, which would 
be the case if they were in the immediate neighbourhood. The tubes 
connecting the pump to the cock-board, for instance, are made of 
iron or steel. !). 
1) Lhe bell wires are either made of iron coated by india-‘ubber or ate protected 
by iron tubes, 
