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Chemistry. — “On Isomorphous Compounds of Gold and Mercury.” 
By Prof. Tu. H. Benrens. 
In his Manual of Microchemical Analysis the auther has pointed 
to analogies between thiocyanates of gold and mercury. 
Renewed investigation of this subject has shown, that the iso- 
morphism of these double thiocyanates cannot be fully established 
by means of compound crystals. Halogen compounds have then been 
tried, and from these complete series of compound crystals have 
been obtained. They were prepared by adding to mixed solutions 
of the chlorides and bromides of gold and mercury chlorides or 
bromides of thallium, caesium and rubidium. Thallous compounds 
act promptly; the compound crystals are interspersed with flakes of 
trichloride or tribromide of thallium. The action of caesium and 
rubidium compounds is slower and less energetic. It can be hastened 
and furthered by adding about one tenth part of alcohol. This takes 
up one third of the halogen, that was combined with gold (shown 
by a change of colour in the solution of bromides) while gold dichlo- 
ride or — dibromide is fixed in the compound crystals along with 
dichloride or dibromide of mercury. If no alcohol is added the 
halogen, split off from the gold trihaloid must form trihaloid of 
caesium or rubidium, which is also readily attacked by hydrolysis. 
Finally it may be mentioned, that the compound crystals of 
bromides will be found useful in testing for gold. With caesium 
the solubility is small, and the yellow colour of the crystals is seen 
without difficulty with a proportion of one part of gold to fifty parts 
of mercury. 
Physics. — Prof. J. D. vaN DER WAALS presents on behalf of 
Dr. G. BAKKER of Schiedam a paper on: “A remark 
on the Molecular Potential Function of Prof. VAN DER WAALS.” 
In his ,Thermodynamische Theorie der Capillariteit in de onder- 
stelling van continue dichtheidsverandering”’ Prof. VAN DER WAALS 
finds for the potential of two material points at a distance r the 
expression 
dh 
BEC etn 
Je 
in which C, f and À represent the constants. 
