Ge bietines 
XX.—On Dimethyl-Thetine and its Derivatives. By Professor Crum Brown 
and Dr E. A. LETTS. 
(Read 24th November 1873 and 4th May 1874.) 
(Sent for Publication 19th August 1878.) 
The analogies existing between elements belonging to one “ family,” such, 
for instance, as the nitrogen family or the sulphur family, have long been 
recognised, and are pointed out and insisted upon even in elementary text- 
books; but the very important analogies existing between substances of 
different quantivalence are apt to be forgotten or overlooked. For illustra- 
tions of such analogies we may point to boron and silicon, elements closely 
resembling one another in themselves and also in their compounds,—differing, 
indeed, in little else but that the one is triad and the other tetrad. <A similar 
relation exists between gold and platinum. 
The elementary substances, sulphur and phosphorus, have many points of 
similarity : both fuse at a comparatively low temperature, both are transformed 
by heat into amorphous insoluble modifications, and both have anomalous 
vapour densities. 
If we turn to their chemical relations and examine the compounds which 
they form, we find similarities of a very striking kind,—similarities as close as 
the difference in quantivalence of the two elements will allow. 
To illustrate this we have arranged some typical compounds of sulphur and 
of phosphorus in parallel columns— 



pez Pp”, Ss Sac Se 
PH, SH, 
PR, SR, 
PRI SR,I 
PR,(OH) SR,(OH) 
P.O, SO, 
P(OH), or | LOH(OH), SO(OH), or | S0,H(OH) 
PR,O SON renal) Ie So, 
PR,O(OH | 
PRO(OH). \ SRO(OH) and | SRO,(OH) 
P.O, SO, 
PO(OH), S0,(OH), 
(PO),0(0H), ($0,),0(01), 




This analogy is not confined to the formule of the substances; the sub- 
| Stances themselves have close resemblances, as any one can see by running the 
eye over the list given above. It will further be noticed, that in compounds 
VOL. XXVIII. PART II. fi 
