;oo SCIENCE PROGRESS 



sufficient residual affinity to make this addition possible, and 

 accordingly rearrangement occurs in both molecules with the 

 setting up of the more symmetric tetrahedral configurations : 



H 



i 



■L ;• — > 



Hv 7H 



In this additive compound the three methyl groups are held in 

 position by the principal valencies of the boron atom, while the 

 ammonia group is held in position by the mutual action of the 

 residual affinity of the boron and nitrogen atoms. 



The addition of ammonia to tertiary pentane, C(CH 3 ) 4 would 

 destroy and not increase the existing symmetry of the molecule, 

 and hence this combination does not occur. In the struggle for 

 existence among chemical compounds the most symmetrical 

 types tend to survive. 



Boron combines with aryl radicals, and phenylboron di- 

 chloride results from the interaction of boron trichloride and 

 mercury diphenyl. This dichloride is decomposed by water, 

 3'ielding phenylboric acid, C 6 H 5 . B(OH) 2 , which is an antiseptic 

 far more powerful than boric acid. Both acids are volatile 

 in steam. 



The alkyl derivatives of aluminium obtained by the action 

 of the metal on mercury alkyls are spontaneously inflammable 

 in air and are at once decomposed by water : 



A1(C 2 H 5 ) 3 + 3 H 2 = Al(OH) 8 + 3C 2 H 6 . 



Aryl derivatives have not been obtained. 1 

 Gallium and indium are extremely rare metals, and hitherto 

 only alkyl derivatives of the latter have been studied. 



Thallium readily yields both alkyl and aryl derivatives : 



TICI3 + Zn(C 2 H 5 ) 3 = ZnCl 2 + T1(C 2 H 5 ) 2 C1. 

 The product, thallic diethyl chloride, can be converted into 



1 Aluminium triphenyl has recently been prepared {Ber. 1912,45, 2828) from 

 aluminium foil and mercury diphenyl as a very unstable solid decomposed by 

 water and not distillable even in vacuo. 



