B— CHEMISTRY 45 



suggested that its constitution should be represented in some such way 

 as : 



CHg Br 



" \ / 

 Br ^-zz^ Au 



/ \ 

 C.Hj NH2— C2H4— NCC^H^), 



rC^Hs NH^ 



\ ^1 

 Au C2H4 



/ K\ 

 .C^H, N(C,H,), J 



This appears to be an unique case of tautomerism, of course, not reson- 

 ance. The compound, with others, is still under investigation and another 

 anomaly remains to be explained. The compound is dissociated in 

 aqueous solution, but shows considerable association in organic solvents 

 (approximately bimolecular in bromoform and quadrimolecular in ben- 

 zene), and it is suggested that the association may be explained thus : 



NEtg NEta NEta 

 C2H4 C2H4 C2H4 

 NH2 NH2 NH2 

 , Et— Au— Br -> Au— Br ^ Au— Br -> 



Et Et Et Et Et 



the auric gold atoms, (2), (3), etc., being 5-covalent — probably not a 

 stable covalency — their Effective Atomic Numbers becoming 86 (the 

 atomic number of radon) whereas the auric gold atom (i), as in a normal 

 auric compound, is 4-covalent and has an Effective Atomic Number 

 of 84. 



(b) Monoalkyldibromo compounds (Pope and Gibson 1907, Burawoy and 

 Gibson 1934 and 1935). 



The monoethyl and mono-«-propyldibromo compounds have been 

 studied in some detail. They are easily prepared by the action of the 

 calculated quantity of bromine on the dialkylmonobromogold compounds 

 in chloroform or carbon tetrachloride solution. They are highly 

 crystalline and deep red in colour ; they are soluble in solvents which 

 are not readily brominated or oxidised and therefore unstable in such 

 solvents as ether, alcohol, acetone, benzene, ligroin, etc. Their molecular 

 weights (determined in freezing bromoform) show that their general 

 formula is (RAuBr2)2 and the high dipole moment in carbon tetrachloride 

 solution of the w-propyl compound {\i = 6t>) affords proof that the con- 

 stitution of these auric compounds is correctly represented thus : 



R Br Br 



\ / ^ / 

 Au Au 



/ \ X \„ 



R Br Br 



