(181) 
in the room a the gas is compressed in three steps, first in the 
room a itself, whence it escapes through valves, then in the annular 
space b, and lastly in the narrower and also annular space ec, which 
it enters also through valves, and whence it goes over the cooling 
spiral 4, through a feeding valve and passing a safety valve to the 
separator S. When the cock #, of this is shut, the gas may 
escape along a little screw *) as well as through the safety-valve. 
The safety-valve comes into use only when the former is screwed 
tight and with the Leiden arrangement the gas, mixed with liquid, 
escaping from it is conducted back to the sucking-tube Aj. When 
the gas has reached a sufficient pressure by opening /, it is admitted 
into the separator, where the liquid gathers below and from which 
the gas may be conducted through the cock #9. Thence it reaches first 
the wide drying-tube ; and then the narrower one Dg. In both it passes 
through P,O;, shut up between glass-wool and asbestos by means 
of gauze and little sieves *). Through cock A, and tube S,, the com- 
pressed and dry gas may be led to the apparatus where we wish to 
bring it; generally a tube like D,, filled only with glass-wool, is 
added in order to arrest the P.O; possibly carried over as dust. 
The lubricating liquid flows in at the sucking chamber through 
the tube f} from the reservoir f4. Care should be taken that this 
reservoir remains filled, (the best way is to keep the level constant) 
and to watch by means of the glass tube #, partly enclosed in brass, 
the regulation of the little jet by the cock f5. (Compare for the 
construction Pl. I[I fig. 5). 
The liquid from the separator is forced through the cock A, 
and the tube Ss into the reservoir V, whence the gas dissolved in 
or escaping after the liquid returns along A (PL IV) to the sucking 
tube g, °). This arrangement besides that at the safety valve described 
above is intended to prevent the loss of pure gas, which usually is 
costly. The glass tubes cemented in brass-pieces J,, l with taps 
(see Pl. III fig. 5). allow us to see whether chiefly liquid or gas 
is forced out. A gauge-glass indicates the level of the liquid and a 
») This little screw is not to be seen in the section represented, it is useful when 
starting the compressor, especially as it allows liquid to escape from the cooling- 
spiral, 
*) Fig. 6 gives a section of these frequently used drying tubes, mentioned in N°, 14, 
and to be found in the drawing of Marutas and in other of these communications. 
The construction is cheap and fit for pressures up to 80 atmospheres. The brass nuts 
have been screwed and soldered onto a gaspipe tested up to 200 atm. and provided 
with a screw thread. The drawing should require no further explanation. 
*) The cock A, is always opened while working with the apparatus but is useful 
to test the tightness of the apparatus, 
