823 



of the well-known Caillktkt form. The quantity of gas ismeasnred 

 at low pressure, tlie piezometei- is placed in a steel vessel tilled for 

 the greater part with incrcurv and further with a transmission 

 liquid; and by then forcing u|) Ihis li(|uid by means of a hydrostatic 

 press we expel the gas from the piezometer reservoir, and convey 

 it to the calibrated stem. Through this way of procedure, however, 

 we are compelled to continc ourselves (o a comparatively small 

 quantity of gas. For if we should want to start from e.g. 1 /. of 

 gas under normal circumstances, the steel pressure vessel must itself 

 have at least a capacity of 2 /. And (o construct a vessel of such 

 a capacity, which can be perfectly closed, and does not leak at 

 3000 atm., is, if feasible, so expensive that its execution is entirely 

 out of the question. Yet it is very desirable not to work with small 

 quantities that the volumes may not become too small at high 

 pressure. To enable us to work with a quantity- of gas of 1 /. 

 without the parts of the apparatus exposed to high pressures becoming 

 of too large dimensions, an apparatus was constructed which allows 

 us to compress the quantity of gas to be measured tirst to from 

 50 to 100 atm., and then convey it to the measuring tube proper. 



A tirst requirement is that throughout the experiment the measuring 

 tube must be continually exposed to the same pressure outside and inside, 

 because else the thin glass tube of course at once gives way. Originally 

 it was the intention to convey the quantity of gas quantitatively into the 

 measuring tube, after its normal volume had been determined. Owing 

 to unforeseen difficulties, to which we shall revert further on, we 

 have not yet succeeded in realizing this quantitative transferrence, 

 so that in the experiments which will be described in what follows, 

 the quantity of gas which was worked with, has been only deter- 

 mined by a measurement of its volume e.g. at 100 atm., the com- 

 pressibility between 1 and 100 atm. haxing to appear from separate 

 determinations. We shall discuss this more extensively later on in 

 the description of the experiments, and shall now first pi'oceed to 

 give a description of the apparatus, used for the conveyance of the 

 gas into the measuring tube. 



It consists of three pressure stages : an (unprotected) glass part 

 for the pressures below two atmospheres ; a part that serves to 

 compress the gas from 2 to 50 or 100 atm.; and the measuring 

 part proper. The glass pai't consists of a vessel A of a capacity of 

 + 1 /. ^), placed in a copper thermostat with glass windows (repre- 



') As we have not made use of the accurate capacity of this vessel for the 

 experiments which will first be describerl. we shall not enter into a description of 

 its calibration as yet. 



53 



Proceedings Royal Acad. Amsterdam. Vol. XVi. 



