B.— CHEMISTRY 



39 



in which, of course, the aurous gold atom is 2-covalent, the compound 

 being of the same type as the well-known potassium aurocyanide, 

 K[N=C— Au — CsN], already mentioned. 



The halogenoaurates, probably the best known auric compounds, 

 have been long known as salts of acids which have been fully investigated 

 and which have the constitution : 



rx 



H 



xn 



Au 



/ 



(X = halogen, CI or Br). 



.XX, 



Some more recently investigated compounds belonging to this type 



are : 



hydronitratoauric acid (Schottlander 1884, Jeffrey 19 16) 



•3H,0 



H 



"NO, NO3- 



\ / 

 Au 



NO, 



NO, 



'3 ^"^3. 



having the same number of molecules of water of crystallisation as hydro- 

 chloro- and hydrobromoauric acids as usually prepared, hydrodi- 

 succinimidochloroauric acid (Pope 1931) 



CI OC— CHr 



H 



■CH2— CO 



N— Au— N 



_CH2— CO CI OC— CH2_ 



hydrodiphthalimidohydroxyauric acid (Gibson and Tyabji 1937) 



CO OH OC 



r , 



[ CsH, 



L ^ 



N— Au— N 



CgHi 



CO OH OC 



and hydrodimethylglyoximinylbromoauric acid (Brain and Gibson 1937) 



rCH,— C=N~0 Br" 



H 



Au 



CH,— C-N— O 



U.*-'^^3 



Br, 



In all these compounds, the 4-covalency of the auric gold atom is obvious, 

 but it is only recently that the persistency of the 4-covalency of auric 

 gold in all its compounds has been recognised. Before the beginning 

 of the present series of investigations in my laboratory, it was shown by 

 W. Fischer (1929) that the molecular formula of auric chloride (trichloro- 

 gold) as determined by Horstmann's vapour pressure and transport 



