398 
PROFESSOR J. W. MALLET OE" THE ATOMIC WEIGHT OF GOLH. 
For all these earlier experiments details are wanting as to the exact mode of 
purification of the gold aud other materials used, and in the weighings there appears 
to have been no correction introduced for atmospheric buoyancy ; the results doubtless 
represent apparent, not absolute, weights, 
[There is also to be quoted the statemeut of Julius Thomsen,'" that he found in 
hydrogen brom-aurate (AuBr 3 .HBr. 5 H 3 O) 32T1 per cent, of gold and 52‘00 per 
cent, of bromine, from which he concluded that Au = probably about 197. Taking 
Br = 7976, and calculating from the ratio of Biy : Au, the number is 197'01.] 
Recent Careful Determinations of the Atomic V/eight of Gold. 
A. Exjieviments of Gerhard Kruss, 1886.t—The author has described in detail 
the means resorted to for the preparation of pure metallic gold, and especially for its 
separation from silver and the metals of the platinum group, with an account of the 
spectroscopic examination of the gold employed. He has then given a full account 
of:— a. His determinations of the gold and chlorine (the former reduced by a stream 
of sulphur dioxide; the latter precipitated and weighed as silver chloride) in a neutral 
solution of auric chloride, prepared by tbe action of water on the so-called auro-auric 
chloride (AuoCl^),! itself prepared by the direct action of chlorine on metallic gold ; 
6 . Like determinations of gold and chlorine in sublimed auric chloride, made by 
direct action of the elements on each other with careful regulation of the temperature ; 
c. Determinations of the gold in a.weighed quantity of potassium auri-bromide 
(KAuBiq), the metal in some experiments reduced from a solution of the salt by 
sulphurous acid, in others reduced from the dry salt by heating in a ’stream of 
hydrogen; d. Determinations of the gold and bromine (the former thrown down by 
sulphurous acid ; the latter precipitated as silver bromide) in the same salt, potassium 
a,uri-bromide ; e. Determinations of the loss of weight (representing 3 atoms of 
bromine for 1 of gold) undergone by heating potassium auri-bromide gradually to 
320° C., towards the end in a stream of hydrogen; f Determinations of the 
quantity of potassium bromide recovered from the residue left in the experiments of 
e by treatment of this residue with water, separation of the metallic gold, careful 
evaporation of the liquid, and final cautious heating of the potassium bromide over a 
free flame. In the experiments of series a account was taken of the somewhat 
difierent processes of purification of the gold used, but, no corresponding differences 
* ‘ Journ. Prakt. Chem.,’ vol. 13, 1876, p. 345. 
f ‘ Liebig’s Annalen,’ vol. 238, p. 30; aud separate publication, G. Kkuss, ‘ Uutersuchungen iiber das 
Atomgewicbt des Goldes,’ Miinchen, 1886. 
t Kruss has in a later paper (‘ Berichte Deutsch. Chem. Gesell.,’ vol. 20, p. 2634) denied the 
existence of auro-auric chloride as a definite compound, but admits that the substance so described by 
Julius Thomsen yields on treatment -with warm water a solution of pure neutral auric chloride, with 
separation of metallic gold. 
