BRIDGMAN. — THERMODYNAMIC PROPERTIES OF LIQUIDS. 85 



curves will show that this is also the case for the other three tempera- 

 tures, with a single exception. For carbon bisulphide, between 

 11000 and 12000 kgm. there is an increase of compressibility from 

 O.O3IOI to 0.0J02 at 60°, and from O.O3IO3 to 0.0,105 at 80°. The 

 change is very small and may well be due to experimental error. The 

 difference curves show as bewildering small variations with tempera- 

 ture as the thermal dilatation curves, so that it is hopeless to try to 

 explain them in detail at this stage of our knowledge. It would seem, 

 however, that an actual reversal of the effect, that is, a smaller com- 

 pressibility at a higher temperature, does not occur so often as was 

 the case for the dilatation. The reversal of the dilatation was uni- 

 versal for all liquids and took place between 1000 and 3000 kgm. 

 But the reversal of the compressibility, indicated by the difference 

 curve crossing the axis, is sporadic in occurrence, and only once occurs 

 for all temperatures simultaneously. 



Comparison of the curves shows some points of interest. The first 

 three alcohols show a slight kink; propyl alcohol at 3000 kgm., ethyl 

 at 1100, and method possibly at a somewhat lower pressure. Amyl 

 alcohol apparently has lost the kink. These four alcohols show in 

 rather desultory fashion for at least one temperature the temperature 

 reversal at high pressures. Isobutyl alcohol, as we expect, shows 

 the effect of structural variation by curves of different character from 

 the other four alcohols, in that they show no reversal, but decrease 

 with fair regularity under increasing pressure. Isobutyl alcohol is 

 also remarkable for the extremely rapid initial drop of compressi- 

 bility with rising pressure. Ether, the isomer of isobutyl alcohol, 

 still further shows the importance of the structure of the molecule; 

 the difference curves for ether show reversal at high pressures, and 

 are also more widely separated than the curves for isobutyl alcohol. 

 The last six liquids show a somewhat greater temperature effect on 

 compressibility than the first six. Acetone shows a strange maximum 

 in the difference curve between 4000 and 5000. Carbon bisulphide 

 shows greater variations at the highest pressures than any other 

 liquid (it will be remembered that the dilatation curves also show 

 abnormally great variations), and a reversal of the effect at 9000 kgm. 

 simultaneous for all temperatures. This simultaneous reversal is 

 shown by no other liquid, and reminds one of the dilatation. Phos- 

 phorus trichloride shows no marked features; the compressibility 

 curves are liot so simple as the dilatation curves. The halogen com- 

 pounds do not show any marked similarities. Ethyl chloride is with- 

 out particular features. Ethyl bromide has a very pronounced 



