460 



miicli smaller and that tliereby the time required for a complete 

 measuiemenl is considerably shortened, which will as a iiile 

 increase the accuracy of a measurement, specially in view of the 

 constancy of the room-temperature. Tlie indicator used by us was 

 the closed workinj^ manometer going from 20 to 60 atmospheres 

 which was referred to in Comm. 78 and did and which we shall 

 call J/jo- Its accui'acy at 60 atmospheres can be put at about ïöVö- 



At the time when Comm. 106 was published some progress had 

 been made beyond the condition described in Comm. 100, not only 

 with the pressure-measurement, but also with the arrangement of 

 the further apparatus required for the higher pressures. This progress 

 especially concerns a new auxiliary manometer, a closed hydrogen- 

 manometer of very nearly the same model as Mf„, but arranged 

 for the pressure-range of 60 — 120 atmospheres. This manometer 

 which we shall call il/u,, is represented diagram matically in Plate 1 

 of communication 146c. ^/„ will similarly be found represented as 

 C in PI. I of Comm. d7a fig. 1. Both are constructed according to 

 the system described in communication 50. M,,„ has a vessel twice 

 as large a iM„„. 



When the pressure-cylinders in the apparatus of Comm. 50 were 

 made, the MANNESMANN-process was not yet available. It was utilized, 

 however, in the construction of Al^^^ and the pressure-cylinder can 

 thus stand a much higher pressure. There is moreover an improvement 

 in the mounting of the manometer, which consists principally in the 

 mercury entering the cylinder from below, as in the closed mano- 

 meters de.scribed in Comm. 50. The mounting is for the rest in 

 every respect similar to that of the pressure-cylinder, represented in 

 fig. 3 Plate I Comm. 97^?. 



The measuring tube of the manometer had been calibrated with 

 great care by Dr. C. Braak. We completed the manometer and 

 filled it with distilled hydrogen (Comm. 94/, XIV). For its further 

 arrangement and the method of using it in the experiments we may 

 refer to previous communicatioos. 



By means of the completed apparatus it was possible to carry 

 out the calibration of J/,„ with the slandardmanometer and obtain 

 data in connection with the question which interested us more 

 particularly as to whether Amagat's observaticms which only start 

 at 100 atmospheres would join on properly to accurate measurements 

 with the open gauge. Schalkwuk's measurements with the aid of 

 the same open gauge and the accurate piezometers of Comm. 50 had 

 given rise to some doubt on this point (comp. Comm. 70 cent, 

 towards the end). But as those measurements had not gone beyond 



