680 SCIENCE PROGRESS 



has been called the Volume Anomaly, by analogy with the similar 



Optical Anomaly. It is expressed graphically thus : 



CH 



S \ 

 CH CH 



I II 



CH C— N0 2 



% /•... / 



CH 



If the group be saturated, this anomaly disappears, 

 (ii) Meta Xylene i : 3 C H 4 (CH 3 ) M.V. 140-0. 

 We find that the CH 3 group is equal to 25-5. 



Toluene C 6 H 5 CH 3 V. 118-3. 

 x CH 3 . = C 6 H 5 . CH 3 - C 6 H 5 = 118-3 -92-8 = 25-5 





Para Xylene is 140-6, and O Xylene 138-4. 



The close approximation of the two groups CH 3 causes a 

 contraction owing to residual affinity. 



C— CH 3 C— CH 3 CH 



t, CH CH , , ( CH CH ~ f , CH C— CH 3 -. 



Para , ,, Meta , ,, Ortho . ., s •. 



14 CH CH I3 CH CH— CH 3 J ' 2 CH C— CH 3 ..-' 



% / %/ X / 



C— CH CH CH 



M.V. 140-6 M.V. 140-0 M.V. 138-4 



Calculated 140-6 on supposition of independence of groups. 

 The dotted line illustrates this effect. 



Value for O Nitrotoluene 1 : 2 C 6 H 4 CH 3 N0 2 is 142-7 



CH C 6 H 4 118-3 — 3-2 = 115-1 



S \ N0 2 + 32-0 



CH CH 



I || QH 4 CH 3 N0 2 147-1 



CH C — CHj--. Vol. an. + o. corr. i4 2 '7 



C NCy..-' Obsd. -4-4 



