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Physics. — Communication N° 54 from the Physical Laboratory 
at Leiden by Prof. H. KAMERLINGH Onnes: “Methods and 
Apparatus used in the Cryogenic Laboratory IL: Mercury 
pump for compressing pure and costly gases under high 
pressure’. 
(Read January 27, 1900.) 
§ 1. At the meeting of January 25, 1896 I read the description 
of a compressor which has been repeatedly used for researches in 
the Physical Laboratory. As the reproduction of the drawings be- 
longing to this description was very expensive I had to delay their 
publication. To the description of the cryogenic laboratory by Prof. 
Mararas!) a diagram was added which could serve as a preliminary 
illustration to § 3 of Comm. 14 (Dec. ’94). Of late only I had the 
opportunity to prepare the complete set of drawings for zincogra- 
phical reproduction. These enable me to now describe more fully the 
way in which I have availed myself of Cainteret’s happy idea of 
a mercury pump in order to obtain a compressor of great use in 
researches with compressed gas. 
The compression with mercury has two advantages. If a liquid 
is brought into the pump cylinder of a compressor, we may 
thereby eliminate the clearancespace, if the gas does not dissolve 
perceptibly in this fluid under high pressure. For im this case, the 
gas which is formed during exhaustion from the residual liquid in the 
pump-cylinder will partly fill the latter and its disturbing influence 
will be greater or Jess, as the difference between the exhaustion 
and forcing pressures is greater or less. Therefore with most liquids 
only small differences of pressure between the sucking and com- 
pression sides will be permissible, and if a higher degree of pressure 
is required we shall have to apply compressions in successive pump- 
cylinders as in the BROTERHOOD compressor (Comp. Comm. N°. 51 $5). 
If however mercury is used, there is no objection to raising the 
gas at once from its normal or even its exhausted condition to 
more than 100 atmospheres, if desired *). 
1) EB. Maruras, Le laboratoire eryogène de Leyde. Rev. Gen. de Sciences, 1896, 
pag. 381. 
*) The sudden compression causes a great, generation of heat (as in the case of 
the fire pump) notwithstanding the considerable cooling by the walls and the mercury. 
A mixture which is easily exploded should not be compressed by the pump, as 
it might be ignited by the heating. This occurred once, when methane and oxygen 
became mixed by accident, The manometer was smashed and flung away, a flash of 
fire burst from one of the outlets, and on opening the pump, several parts were found 
to be burned. The explosion fortunately occurred without any personal accident. 
