( 223 ) 



1 °/ a 1,5 7» at 34°. 5 according to the calculations of Verschaffei.T, 

 Coram. Suppl. N". 10. It' the uncertainty of this correction is taken 

 into account, we must come to the conclusion, the limit ofaecuracy 

 of our experiments not being higher than 1 °/o either, that the diffe- 

 rences of density derived by dk Heen from his experiments do not 

 exist for pure CO, when sufficient care is taken to ensure equili- 

 brium of pressure and temperature. 



§ 6. Repetition, of Teichner's experiment. An elaborate description 

 of the apparatus and the operations will be given on another occasion. 

 Here the following remarks may suffice: 



1. Repetition with CO, was considered to be desirable also by 

 Teichner because it gives more warrants for purity. 



2. A platinum-platinum-iridiuni thermo-element (used with a mag- 

 netically protected galvanometer of Dubois) was successfully fused 

 into Teichner's tube at the top and at the lower end, so that the 

 tube remained proof against a pressure of 150 atmospheres. However 

 we did not succeed in making the thermo-elements free from disturbing 

 electromotive forces, nor did they give with certainty the accuracy 

 of 0°.01 we wished. The places of contact were found at l / A and '/« 

 of the height of t lie tube. A third thermo-element to compare the 

 temperature in the tube with that in the bath would be desirable. 



3. The critical density of CO,, 0.469 '), being smaller than that 

 of CC1 <; with which substance Teichner worked, it was much more 

 difficult to obtain the required density-bulbs (small glass bulbs) of 

 0.365, 0.390 and 0.405. We owe them as well as the fusion of the 

 thermo-elements to the skill of Mr. 0. Kesselring, chief of the glass- 

 blowing department of the laboratory. By means of Clebsch's formula 

 it was found that the decrease of volume of the bulbs at the 

 highest pressures can only amount to from 7«oo to '/„,. 



4. Still greater care was devoted to the purification of the CO, 

 than in the repetition of de Heen's experiment. From a metal 

 bottle of CO, as used for the latter, 7, is once more blown off, and 

 then 7s distilled over into a second bottle from which under weighing', 

 so much is suffered to escape that a fixed quantity remains. This 

 second bottle is connected by glass tubes with the experimental tube, 

 a mercury manometer, a mercury airpump and an auxiliary bottle 

 (also of metal) with pure CO, for rinsing the conduits, after which 

 the fixed quantity which it contains, is quite distilled over into the 



!) Derived by Keesom Gomm. N°. 88 These Proc. Jan. 1904, p. 574, from his 

 observations by means of the rule of the rectilinear diameter. 



15 

 Proceedings Royal Acad. Amsterdam. Vol. X. 



