698 SCIENCE PROGRESS 



The case of silicon was worked out by Kipping on the 

 sulphonic acid of benzylethylpropylsilicyl oxide : 



C2H5 



O 



SO3H . C 6 H 4 . CH 2 . Si . 



C 8 H 7 J. 



by crystallising the salts of this acid with optically active d- 

 and /-methylhydrindamines. Pope and Peachy demonstrated 

 the case of tin with the compound methylethyl-w-propyl- 

 stannic iodide, the dextrorotatory component being isolated 

 through the agency of */-camphorsulphonic acid. 



This resolution of silicon and tin asymmetric compounds 

 into optically active components shows that these compounds 

 have the tetrahedral structure characteristic of carbon com- 

 pounds, and that in all probability the above series of tetra- 

 alkyl derivatives are all constituted on the tetrahedral type. 



Such relationships as these afford ample justification for 

 including carbon, silicon, germanium, tin, and lead in the 

 same natural family. 



The points of difference between carbon and silicon are 

 also illustrated by investigations of the organic derivatives of 

 the latter. Kipping and Robison showed that silicones differed 

 from the ketones in having polymerised molecules ; they worked 

 this difference out in the case of benzyl ethyl silicone, which 

 has a trimeric molecule 



[ 



CeHs . CH2\ — l 



/SiO 



C 2 H 5 / J 



3 



unlike the non-polymerised molecule of the ketones RR'CO. 

 This fact helps to explain the difference between the refractory 

 solid oxide, silica [Si0 2 ] x , and the gaseous carbon dioxide C0 2 . 



(b) The Aluminium Family 



The third vertical series is similarly divisible into two natural 

 families, and taking again the capacity for forming organic 

 derivatives as the important criterion of relationship, we find 

 that boron, the initial member of the series, falls into line with 

 aluminium and its homologues in yielding organic derivatives : 



Aluminium family . B Al Ga In Tl 



Rare earth „ Sc Y La, etc. 



The other family containing scandium, yttrium, and some 

 other twelve or thirteen elements of the rare earth series 



