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Physics. — "Isotherms of diatomic gases and their' binary mixtures. 

 VIII. The breaking stress of glass and the use of glass tabes 

 in measurements under high pressure at ordinary and low 

 temperatures". By Dr. H. Kamerlingh Onnes and Dr. C. Braak. 

 (Communication n°. 106 from the Physical Laboratory at 

 Leiden by Dr. H. Kamerlingh Onnes). 



(Communicated in the meeting of April 24, 1908). 



§ 1. Introduction. With former determinations of isotherms (Comms. 

 n os . 78 April 1902, 97- March 1907, 99' Sept. 1907, 1 00" and 100* 

 Dec. 1907, 102« Dec. 1907 and 102* Febr. 1908) we could not 

 raise the pressure above 60 atm. For in order to reach the required 

 accuracy of about Vso«o we want a manometer which is reliable to 

 the same degree. And till now we could only reach this degree ot 

 accuracy by means of a calibration with the open manometer de- 

 scribed in Comm. n°. 44 (Nov. 1898) which reads to 60 atm. only. 

 Already long ago we intended to include the higher pressures in our 

 investigation. As a first step in that direction we have raised the 

 upper limit of the pressure to 120 atmospheres. For while keeping 

 the same arrangement we could easily complete the existing 

 open manometer to one of the same accuracy reading to 120 

 atmospheres by merely adding a number of new manometer tubes 

 of greater resisting power than those we had. 



The new manometer and also the other apparatus intended for 

 pressures to 120 atmospheres are nearly completed and will soon 

 enable us to determine the isotherms to 120 atm. Afterwards we 

 hope that these will be followed by measurements at still higher 

 pressures. It seems even possible to reach 500 atmospheres with 

 almost the same accuracy. 



For all these investigations it is a great advantage when the 

 piezometer- and barometer tubes can be made of glass. Therefore 

 we have investigated in how far this would be possible with regard 

 to the breaking stress of glass. 



The breaking stress of glass has been investigated most at ordinary 

 temperature, because it is in the first place desirable that the 

 reservoirs of the manometer tubes of the open manometer and the 

 divided stems of the piezometer tubes should be made of glass. 



To these measurements we have added a series of determinations 

 at lower temperatures in order to judge to what extent glass piezo- 

 meter reservoirs could be used for the higher pressures at these 

 temperatures. 



