(457) 
S5. The auxiliary compressor itself remains to be described: 
according to the diagram on Pl. III and the detailed drawing on 
Pl. VII, which also (fig. 1) gives a simplified view of the whole 
compressor. It was constructed for me by the Société Génevoise. 
To save room it is suspended on the wall below the driving-shaft 
(§ 2, y at the end) with which also the mercury pump is coupled, 
The plunger / is hollow and surrounds a copper tube, through 
which water for cooling the plunger and compressed gas is con- 
ducted, (see /, and #5 on Pl. III). For admitting and drawing 
off the water india-rubber tubes are used which move together ER 
the plunger and are connected to the water supply. 
The packing ZE} consists of two collars Zj, and Z3 as in the 
forcing-cylinder of the mercury-pump (comp. § 3, «). They are 
placed in opposite directions one to shut during exhaustion, the 
other during compression, and are enclosed by the nut Z, screwed 
against the pump-body D, in which it fits exactly, and which it holds 
by means of a rim Es. The plunger is protected by wooden rings 
(comp. §3, @) and a leather ring Zj; fitting on a bronze ring Zig. 
The outer rim #3 is filled with glycerine. In the nut is a lubricating 
chamber /,, (Pl. VII fig. 3) in which glycerine is brought under 
pressure. The pressure is applied in the storage-bottle through the 
cock C, (see. fig. 2 and 5 Pl. VIT) and the tube G, (fig. 2). Gs, 
is used to test whether the apparatus has been RE filled 
with liquid. The glycerine is hindered from flowing out of this 
chamber by a second collar packing £;,, screwed on by means 
of the nut 4 and the enclosing piece Eis. The problem of 
obtaining only a small clearance gasspace and of allowing as 
little of the lubricant as possible to be in contact with the gas, 
has been solved by turning the plunger so exactly that it fits 
almost hermetically in the pump-cylinder, and further by making 
the bottom of the pump cylinder spherical, and cutting it off so 
that it is wedge shaped with two flat surfaces (those of the valves). 
The whole bottom-piece C of the pump cylinder can be removed, 
which facilitates the cleaning and dismounting of the valves. 
The gas sucked-in is admitted into the pump cylinder through the 
suction-valve C,;, the pressure of this gas can be read on a vacuum- 
meter B (connected with C)), used because the auxiliary compressor also 
serves especially as an air pump, as for instance in the circulation of 
liquid oxygen evaporating under low pressure. The suction-valve is 
kept back by a spring and an adjusting-pin C,, and can be taken 
out of the pump by screwing off Css. The gas is then forced through 
the compression-valve (the drawings of compression-valve and suction- 
33 
Proceedings Royal Acad, Amsterdam. Vol. IL, 
