G99 



large electromagnci /,. and in llie fixed coil y are adjusted to suitable 

 whole numbers and (he current 4 (in Ihe movable coil) regnlated 

 by a gradual change of the resistance until the carrier has come back 

 to the zero. The current /,„ is then noted down and the operations are 

 repeated for the 4 possible combiiuxlions of the currents 4, if and 

 /,, . Before and after each observation Ihe zero-position of the carrier 

 is observed or again adjusted ; when the change amounts to only a 

 few tenths of a millimetre, there is no objection to do this, more 

 simplj than by means of the plunger, by shifting the microscope 

 a little. 



{To be continued). 



Chemistry. — "The application of the tlieory of allotropy to electro- 

 motive equilibria." By. Prof. A. Smits. (Communicated by 

 Prof. J. D. VAN DÈR Waals.) 



1. I communicated already before ^) that the investigation for 

 testing the theory of allotropy witli different elements and anorganic 

 as well as organic compounds was in progrese. The investigation of 

 the metals, which had been started with tin and mercury, was 

 somewhat delayed, because all the time had to be devoted to the 

 study of phosphorus and rnei-cury-iodide, so that only comparatively 

 shortly ago the metals could be taken in hand again. 



As may be supposed as known, the theory of allotropy rests on 

 this fundamental a.'isumption that every phase of a system that 

 behaves as a unary one is at the least built up of two kinds of 

 molecules which are in internal e(piilibrium, and must necessarily 

 be taken as the components of a pseudo-system. This theory com- 

 prises, therefore, all possible states of aggregation of a substance, and on 

 account of the importance of its conclusions its principial interest lies 

 in the region that has been least investigated up to now, viz. that 

 of the solid state. 



Now it is clear that the experiments which are carried out to 

 test this theory are undertaken in the first place to prove that the 

 different states of aggregation and particularly the solid j)hases of a 

 substance which presents the phenomenon of allotropy, are really 

 mixtures, and in internal ecjuilibrium, for every time that this 

 succeeds a confirmation of the said theory has been found. In the 

 second place an attempt may be made by a continuation of the in- 



1) These Proceedings, April 26, 1912, XIV, p. 119y. 



