( 455 ) 
indicates the connection through a high pressure cock gg with 
a reservoir gs, in which the pressure is read on the manometer q4s 
to be closed by the cock qyg. In this reservoir the gas from the 
cylinder g, which is to be foreed through the regulating-cock g5 is 
generally admitted so that the tension in gg does not rise above 10 
atmospheres. With higher pressures at the beginning or at the end 
the pump might begin to work too heavily and the pump-cylinder 
become warm. Generally before commeucing to force over the gas, 
the pump and the reservoir are exhausted through “2 and O,. If 
the apparatus on the exhaust-side is strong enough, a safety-valve 
may be applied, which conducts gas when the pressure is too 
high on the forcing-side back to the exhaust-side (comp. § 5 C3). 
Because the working of the mercury-pump requires constant attention, 
we may however trust to being warned in time by the manometer 
whilst the safety-cap gives final security. 
I. To work in conjunction with a pump which 
delivers gas under pressure. 
With regard to the mercury-pump itself, the conditions are the same 
as if compressed gas were admitted from a cylinder through g,, and 
it is obvious that we may often avail ourselves of the usefulness 
of my compressor for this purpose. As an example of this I will 
consider here only the case when the auxiliary compressor is espe- 
cially constructed to work together with the mercury-pump, i.e. 
when it transmits exactly so much gas at the highest pressure 
(admitted on the exhaust side of the mercury-pump), as the latter 
can take up. If in such a compressor the gas were also forced by 
means of mercury we would actually have obtained a mercury com- 
pressor with two degrees of pressure and tenfold power. With a 
mercury-pump after the present pattern buth on a somewhat larger 
scale and with a proportionate auxiliary compressor at my disposal, 
I should be able to bring about the long wished for circulation of 
liquid hydrogen in the cryogenic laboratory. In the mean time many 
researches do not involve the great requirements of this last problem, 
nor do they admit the use of a BROTHERHOOD compressor, arranged 
for the compression of large quantities of pure gas as described 
Comm. N°. § 3. For a commencement I found it sufficient to build 
an auxiliary compressor, which in contradistinetion to the BOTHERHOOD 
is meant to be exhausted and in which the gas is compressed by 
a minimum of glycerine. Thereby in contrast with the mereury-pump 
the auxiliary compressor, destined to work with it could be made 
