B.— CHEAilSTRY 55 



concerned. Actually, it would only mean the altering of the position 

 of the auric gold atom from the centre of a square to a position within 

 the pyramid of which the base is the original square ; this may be 

 illustrated by Fig. 5 : 



Br . 



crystalline (BljS.AuBrjJj 



Fig. 5. 



Such a constitution would not be out of keeping with the separation of 

 the two parts of the complex compound in non-aqueous solvents since 

 5-covalent auric compounds may be expected to be unstable (compare 



P- 45)- 



I have elaborated this example to draw attention to the fact that not 



a few present-day investigations of which this is one are accumulating 

 in which chemists will have to rely almost completely on crystallographic 

 technique for the determination of the constitution of substances whose 

 structures have so far not proved amenable to elucidation by treatment 

 by the older methods. In the present instance, the above suggestions 

 have been excluded at once by my collaborators, H. M. Powell and R. F. 

 Phillips at Oxford. There are no indications of the 'bridge ' and ' ring ' 

 structures now well known from previous investigations, and there kre 

 no indications of such a disposition of gold, bromine and sulphur atoms 

 as required by the structure indicated in Fig. 5. In other words, this 

 work again reveals the small tendency — if any — of aurous gold to become 

 4-covalent and of auric gold to become 5-covalent. Finally, having ex- 

 cluded the direct linking of the auric and aurous parts of the complex, 

 there remains apparently only the possibility of the fitting together 

 in the solid state of the aurous and auric compounds by a close 

 packing arrangement which, again, only the crystallographer is capable 

 of resolving. The result of this crystallographic investigation will be 

 awaited by me with some interest, and it may be that investigations such 

 as this will give some useful information about ' complex molecules ' 

 generally. 



There are still many problems, some of them fundamental, in the 

 chemistry of gold waiting to be solved. Even as it is, I have only men- 

 tioned a few of those which my co-workers and I have tried and are 

 trying to investigate ; but there is a limit to the topics which can be 

 discussed at any one time and I venture to conclude with the apology 

 of that interesting man of the world, chemist and theologian, Richard 

 Watson, D.D., F.R.S., sometime Professor of Chemistry in the University 

 of Cambridge, later Regius Professor of Divinity and Bishop of Llandaff : 

 ' Chemists must excuse me, as well for having explained common 



