( 439 ) 
most halves in front elevation, and of the whole in side elevation !). 
We now come to a more complete explanation of the desirability 
of the most important changes®). A survey of these has been given 
in § 3 Comm. No. 14 (Dec. ’94), to which a reference should be 
made in the first place. 
41. It was necessary to arrange that air can not get into the 
pump tube through the packing (comp. 0, Pl. I fig. 1). 
%2. The piston can not be damaged through insufficient lubri- 
cation and hence cause the packing to fail to give adequate closure. 
UB. The mercury can not be soiled by the lubricant. 
When the latter occurs the scum which gathers near the forcing- 
valve, keeps back the high pressure gas below this and enables 
mercury and then gas to leak back from the reservoir under high 
pressure. Therefore it is of the greatest importance that the mercury 
remains quite clean. My principal desire in most of the changes 
was to enable me to accomplish this. 
It was possible to attain all these requirements by transferring 
the plunger, which by moving upwards in CaILLETET’s compressor 
causes the compression of the gas (comp. a fig. 1, Pl. I) to a separate 
compression tube C’ Pl. III. From this through a wide connecting 
tube d, as shown in the diagram, it moves the mercury in the pump- 
cylinder e up and down. The lubricant used was glycerine, which 
gives a sufficient lubrication and yet as is the case with vaseline 
and more especially oils, does not unite with mercury by agitation 
to a butterlike substance (see especially % 3). 
Contact of the mercury with the packing is wholly avoided by 
introducing a layer of glycerine above the mercury, which can be 
done now that the packing is above and not under the mercury. 
The stuffing box b is entirely immersed in glycerine, so that the 
pump can only suck in glycerine, if the packing does not fit 
tightly; should however air enter it might cause the pump to stop 
working but could not mix with the experimental gas. This could 
only take place if the mercury and the glycerine were entirely forced 
1) The resemblance of the forms makes it easy to find our way on the drawings, 
moreover the letters have been chosen so that the letter itself indicates a distinct 
part of the apparatus, the annexed numeral a certain detail of that part, and following 
numerals details of that detail. 
*) Some of the newly added pieces were constructed with much care by Mr. 
J. W. Grrray (formerly Kipp & Sons); to Messrs. Kouw and Curvers, mechanics 
at the laboratory I owe my best thanks for the extreme care with which they have 
assisted me in these alterations, 
