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Physics. "On plaitpoint temperatures of the system tvater-phenol" . 

 \\\ A. Keesing. Communicated by Prof. J. D. vander Waals). 



According to observations l>\ I.kiii i.i.dt. \. d. Lee, and Schreine- 

 makers the system water-phenol possesses maximum pressure al low 

 temperatures. So theoretically a minimum critical temperature was 

 to be expected, but as water shows abnormal deviations in other 

 respects, an elaborate investigation was desirable. In view of the 

 high critical temperatures of the components (water 365°,0 according 

 to Cailletet and Colardeau, or 364°,3 according to Battelu ; phenol 

 419 :> ,2 according to Radice) and the impossibility of using glass test- 

 tubes glass dissolves in water at such a high temperature a con- 

 clusive investigation had not yet taken place as far as is known. 

 Experimenting in a way similar to that indicated by Schamhardt a ) 

 I have succeeded in arriving al a preliminary result. 



As for the determination of the plaitpoint temperature there was 

 no need for me to regulate either the pressure or the volume I <li<l 

 not want a Cailletet tube, but iisr<l small closed test-tubes ol 

 quartz. This made ii possible tor me to use a vapour-jacket whose 

 bottom was also glass, and which rested on asbestic iron gauze. 

 In consequence of this one of the two nickelin wires, viz. the 

 one used by Schamhardt to heat liis boiling-liquid, could be dis- 

 pensed with, and replaced In a Bi nsen burner. The -croud wire, 

 which enabled him to prevent satisfactorily the radiation at tem- 

 peratures between 200 and 300 3 , proved insufficient for tempe- 

 ratures between 350° and 4<><> . A second layer of asbestos round 

 the wire gave some improvement, but the radiation appeared to 

 be completely prevented only when I placed a glass cylindre 

 silvered on the inside, in which two slits were left free lor reading-, 

 round the vapour-jacket, which had been thus wrapped up. This cylindre 

 of a diameter 5 centimeters larger than that of the jacket, was shut 

 off by mean- ol' asbestos wool on the upper and the lower side. 



It was not without difficulty that we found a boiling-liquid, for 

 in the Phys. ('hem. tables ol' Landolt-Börnstein no boiling-liquids 

 arc given above 360°. I u^<\ benzidine, an inactive substance, which 

 boils at 1 atm. pressure at ^400 with colourless vapour. We 

 have, however, to hear in mind: 



1. that chemically pure benzidine be used, because impure ben- 

 zidine boils irregularly, ami covers the vapour-jacket, the quartz 

 tube, and the thermometer with a lough, tarry layer, which prevents 



!) H. 0. Schamhardt. Isotherms of mixtures of henzen.; and aether. Thesis 

 for the doctorate p. 12 — 16. 



