( 1^7 ) 



and bases, where / = nearly 2, this number becomes 650 gr, cal. 



So e. g. for KCl, of wliicli the heat of ionisalion of 1 gr.mol. 

 =: — 720 gr. cal. ^), the total heat of mixing with much H,0, 

 (excluded the change in |)Otential energy) will therefore be not — 720 

 gr. cal., but only — 720 -\- B50 := — 7() gr. cal. 



So it is seen, that the order of magnilude of the heat to be expected, 

 can be totally modilied, and that in genei'al a great mistake would 

 be committed, when we neglected the above calculated 326 /gr. cal. 

 in the calculation of the heat of mixing. 



Therefore, with diluted solutions oi' non-c/ectro I i/t<'s in associating so\- 

 vents, 325 gr. c.al. on each gr. mol. of the solved substance must 

 always be subtracted from the absorbed heat determined by experiment, 

 in order to calculate the pufc (absorbed) heat of mixing, that is to 

 say that heat, which is caused solely by the change in [)otential energy. 



Physics. — Prof. Bakhuis Roozkboom, in the name of Dr. A. Smits, 

 presents a paper, entitled: '^Oii the phenomena appearinu when 

 in a binary system the plaitpointcurve meets the solubility curve." 

 (Third communication). '^) 



(Communicated in the Meeting of June 25. 1904). 



The previous qualitative examination of the binary system etiier- 

 anthraqui]ione show^ed that a good survey of the whole could only 

 be obtained by continuing the examination in quantitative direction 

 with the aid of the pump of Cailletet. 



Some difficulties were to be foreseen ; the investigation would have 

 to be extended over a range of temperature from ± 170° to rt 300", 

 in which the pressure might be expected to I'eacli a pi-etty conside- 

 rable amount — and the combination of high tenq)eraturc and high 

 [)ressure being exactly the thing against whicii glass is but seldom 

 proof, it seemed at first that we should meet wi(h great experimental 

 difticulties in the (|uanlilalive examination. The experiment however 

 showed that the pressures were not exceedingly high ; it apj)eared 

 a maximum pressure of 100 atm. would suflice, and this pressure 

 Jena-glass could withstand up to more than 30(P '). 



1) Z. f. Ph. Ch., 24, p. Gil (1897); Lelub. tier math. Chem., p. .53 (1901). 



2) This paper is a continuation of the two preceding ones on the system etlicr- 

 anthraquino)ie. The title chosen first seemed to me undesirable and was therefore 

 modified. 



=') With pleasure I avail myself of this opportunity to thank professor K.\MERLiNCin 

 OxNFS for his kindness towards mo in procuring the necessary information and in 

 lendius; me some instruments wanted. 



