( 631 ) 



mol., which is in acoonhmce with the observations of.IoNKs, ('mamhers 

 and Frazer ^). 



The first wlio by the cjToscopic way discovei-ed minima in (he 

 moIecnUir lowering of the freezing- point for chlorides of the alkali 

 metals below the concentration 1 gr. mol., were Jones and Getman '^), 

 Avho published their results in the newly publislied Juhelhaml fi'ir 

 Osttvald. It is remarkabl'3 that working with the common ai)paratus 

 of Beckmann these observers obtained more accurate results than Raoult 

 with his apparently ideal apparatus. For Raoult found forNaCl-solutions 

 np to the concentration 1 gr. mol. a regular decrease of the molecular 

 lowering of the fi-eezing i)oint with increase of the concentration. 



2. After having thus shortly pointed out what the boiling point 

 method, the vapour tension method and the freezing point method 

 liave lirought to light for the stu»ly of the non-diluted solutions, I 

 proceed to give the results of the determinations of the diminution 

 of the vapour tension of NaCl and NaNO^-solutions, made by means 

 of the mlcroinanometei', in which the aniline-water-manometer was 

 replaced by the manometer of Lord Rayt-eigh ^). It seemed namely 

 ver}' desirable for the greater certainty of the results, to repeat 

 some measurements with another apparatus, the accuracy of which 

 did not differ too much from that of my manometer. Lord Rayleigh's 

 invention was therefore very welcome to me, because his manometer 

 was stated to reach an accuracy of ± 0.00045 m.m. Hg, and mine 

 had an accuracy of 0.00025 m.m. Hg. 



Lord Rayleigh's manometer and the arrangement of this apparatus 

 has been represented in iig. 1 and 2. A is a barometer tube, which 

 branches into two parts at the top; the two branches are blown out 

 to two bulbs of ± 25 mm. diameter at BB. In these bulbs extend 

 two finely drawn out glass points, which are ground off to a sharp 

 point at the lower end. On the tubes LL, of wdiich the one more 

 to the left is split up into two branches, as is seen in the horizontal 

 projection, and which thus furnish three points of support, a glass 

 plate X is laid which bears a mirror M, whose front is silvered. 

 The glass plate X is fastened to the three points of support and 

 the mirror M to the glass plate by means of water glass. 



Lord Rayleigh had connected the tubes CC with his apparatus by 

 means of straight glass tubes 3 meters long, but here some glass 

 spirals ± 35 c.ul long have been added between them in order to 

 prevent any Avrenching. 



1) Araer. chem. Journ. 23, 89 (1900) ; ib. 23, 512 (1900). 



2) Zeitschr. f. Phy.sik chcm. 46, 2ii (1903). 

 s) Zeitschr. f. Phvsik chem. 37, 713 (1901). 



42 



Proceedings Royal Acad. Amsterdam. Vol, VI. 



