833 



way leads on one side to llie "hciid" of (lie lillle pressure hjihiiice, 

 on the other side to iin iiecnrate spring-nuinonieter, vvhicii Ccin 

 indicate up to 300 atm. As has been said above, during tlie 

 time that there is no communication between inside and outside of 

 tiie measuring tube tiie pressure is regulated witli tiie aid of this 

 spring manometer. 



On the large press stands a large spring manometer of Scmakfkk 

 and BuDENBERG, wliich can be used up to 5000 atm. ; it serves for 

 a preliminary orientation about the [)re vailing pressure. 



0. The temperature measurement. 



It was originally the intention to measure the temperature im- 

 mediately by the side of the measuring tube, so inside the vessel L. 

 The third and fourth insulated wires in the [)iece M were at first 

 destined for this purpose. But an accurate preliminary investigation, 

 directed to this end, showed that no accurate temperature n'leasure- 

 ment could thus be attained. For as Liselt. and Lussana have already 

 demonstrated, the resistance of a metal wire does not only change 

 in consequence of the temperature, but also through the pressure. 

 And this latter variation appeared to be by no means regular. After 

 increase of pressure a wire sometimes returned to its original re- 

 sistance at atmospheric, pressure, sometimes [)ermanent changes of 

 resistance appeared. Besides it would have to be ascertained empiri- 

 cally separately for every wire, how much the change of the resist- 

 ance with the pressure is, for these changes are by no means equal 

 for wires of seemingly the same material. It is, however, required 

 for such a gauging of the resistance wire that the wire can be 

 placed under different pressures in the pressure apparatus, the tem- 

 perature being left constant. This can practically not be achieved in 

 another way than by enclosing the whole pressure apparatus in a 

 thermostat, and by taking, under the necessary i)recautions, the tem- 

 perature of the thermostat for the temperature of the resistance wiie 

 under pressure. But then it is much sim{)ler to ap[)ly the same thing 

 directly in the measurements, and assume then too the temperature 

 of the vessel L and its contents to be equal to that of the surround- 

 ing thermostat. 



A t/iennoscope inside L is, however, indispensable then. In conse- 

 quence of the compression, resp. dilatation heat of the gas in the 

 measuring tube, namely, variations of temperature of the magnitude 

 of one de^a'ee occur inside L. If there is no thcrmoscope inside L, 

 much time may be needlessly lost in making sure that the stationary 



