829 



We should, therefore, take cave that in tliis condition no great 

 variations of pressure can take place, which might make the measur- 

 ing tube burst. This is controlled by a spring manometer, which 

 is in connection with the hydrostatic press. In the operation it appears, 

 however, that a few atmospheres' difference of pressure is not yet 

 dangerous to the measuring tube. The dimensions of the measuring 

 tube must be so chosen in proportion to the jar G that all the gas 

 has been expelled from G and F by mercury before 80 to 100 atm. 

 have been reached, as the unprotected glass tube F cannot resist a 

 higher pressure. Now P is closed. This separates the high pressure 

 division, in which the measurements take place, entirely from the 

 second pressure stage, D etc. For i/lias already been closed (see above). 

 Now T is opened. This opens again the communication (by tiio 

 way Si U Ss P S^ TS^ RQHO) between the inside and the outside 

 of the measuring tube. If we now continue to raise the pressure by 

 the hydrostatic press, the mercury rises in H resp. 0, and pushes 

 the gas further and further above it, till at last the mercury readies 

 the tube N and then the measuring tube. Still further increase of 

 pressure then brings the mercury into contact with the platinum 

 contacts in the measuring tube one after another. All through the 

 measuring tube remains constantly exposed to the same pressure 

 on the inside and on the outside. When we want to suspend the 

 measurements temporarily, this continues to be the case. For then 

 a cock in the hydrostatic press is closed which shuts the 

 conduit iSj. The closure of the apparatus is so perfect that 

 when this cock is closed the high pressure stage {LHRTFU, and 

 the connecting system of tubes) can be left at a few hundreds 

 of atm.'s pressure for weeks, without a trace of leakage being 

 observed. 



This perfect closure is obtained by the application of steel-to- 

 steel closure everywhere. Only in the cock T it is inevitable that 

 liquid under high pressure is in contact with packing material. (In 

 the cocks F and H there is of course also packing material, but 

 this packing material belongs to the second "pressure stage"). 



All the couplings are again of the system indicated in fig. 7 and 8, 

 of course modified according to circumstances at the different places. 

 Thus the couplings for the cock F are represented by tig. 9. A 

 steel cone <j is always found, which is then pressed against the piece 

 with which it is to be connected by a nut K or the flange plate h. 

 Jn the former case the thread of the screw is left-handed, so that 

 when the nuts K are turned on, the cone is screwed tighter, instead 

 of being unscrewed. This precaution is unnecessary in case of a 



