(541 ) 



bj Jackson ^), in which a glass manometer was described which had 

 enabled him to determine pressures below one atmosphere acciiratelj - 

 to tenths of millimeters of mercury. This glass spring, founded on ' 

 the principle of the Bourdon metal barometer, which different from 

 the before proposed models can be made easily and rapidly after 

 some practice, yields a very efficient apparatus for measurements of 

 vapour tensions of substances wliich attack mercury, like nitrogen 

 tetroxide. We have varied the shape, sensitiveness and size of the 

 glass manometer in numerous ways, and have at last succeeded in 

 modifying the method in such a way that it is possible to carry out 

 determinations of the vapour tension also at higher pressure. In this - 

 communication we will discuss the determinations made up to three 

 atmospheres; the description of the experiments at higher pressure, 

 which have already been carried out to about 60 atmospheres, and 

 which if possible will he continued to the critical pressure, will be 

 postponed with the determination (by another method) of the critical 

 temperature (158°,2) to a following communication. 



3. . Glass manometer for pressures below three atmospheres. 



Tjie shape of the glass manometer which was used by us, has 

 been represented in fig. 2 ; it is the same as that of fig. 2 of the cited 

 paper by Jackson. A glass tube of about 5 mm. external section is 

 drawn out on one side; near the drawn end the tube is blown up 

 and drawn out to the shape of an ellipsoid, which is then reduced 

 to the shape of fig. 2 by one-sided heating. If now an increase of 



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1) Journ. Ghera. Soc. 9d 1066 (1911). 



