( 757 ) 



All couplings of the conducting lubes in which air is to be kept 

 at constant pressure, have been placed (cf. the plate to Comin. N°. 94 6 ) 

 in trays filled with oil, according to what has been said in 

 Comm. N°. 94A 



/;. With regard to the means for keeping a constant temperature 

 in the cryostat, the system of pumps and auxiliary arrangements 

 for the regulation of the temperature, belonging to the circulation of 

 oxygen, has been represented in tig. 4 of PI. I. For a description 

 we refer to Comm. N°. 94. 



Some particulars about the ethylene circulation used for the deter- 

 minations of Series I, are to be found in Comm. N°. 94/" XIII § 1. 



§ 3. The manometer. 



The pressure measurements were performed by means of the closed 

 auxiliary manometer described in Comm. N°. 78 r . As a comparison 

 of this manometer made in 1904 with the standard manometer A IV 

 (of Comm. N°. 78 § 17), yielded an unsatisfactory result, and led us 

 to expect that the auxiliary manometer was no longer reliable, it 

 was compared at four points with the open standard manometer, to 

 which the improvements mentioned in Comm. N°. 94 6 were applied 1 ). 

 The results of this comparison have been combined in the subjoined 

 table. 



Column C like column C of table XVII of Comm. N°. 78" repre- 

 sents the reading of the pressure determined with the open mano- 

 meter (Comm. N°. 44). Every value is the mean of two observations. 

 Column F gives the pressure read by means of our closed auxiliary 

 manometer. Each of the values has been obtained as a mean from 

 three observations. In the calculation the calibration derived in Comm. 

 N°. 78° has been used. In column G the difference of the columns 

 F and G is represented, column H contains this same difference 

 expressed in the numbers of column C as unity. The pressure given 

 by the auxiliary manometer appears to be too high for all pressures 

 observed. It was obvious to ascribe this to a too high value assumed 

 for the normal volume 2 ). 



If we take the mean of the values in column H, we find 0.00087. 

 If we diminish the normal-volume and so also the pressures by 

 this part of the original amount, the differences represented in 



1 ) In the investigations with this manometer of Comm. N'. 70 the total absence 

 of leaks was rare; here, however, it was easily brought about. Also the improved 

 coupling of the steel capillaries to the glass-capillaries of the open manometer by 

 platinizing proved satisfactory. (See Comm. N°. 94''). 



2 ) In connection with this diminution of the normal volume see also Comm. 

 N°. 95«, § 11. 



