425 



said curves does not niu parallel (o the xariations of the viscosit}' 

 with temperature. Most strikingly this can be seen in those substances 

 whsre the curvature is so slight, that the curves can be considered 

 to be straight lines : with ethylhenzoate, whose viscosity at 10° is 

 about six times that of acetone, and in a temperature-interval of 

 50° decreases to two or three times that vahie, the /-^curve is a straujht 

 line ; with the isobutylbroinule. whose y^-t-QurxQ between 0° and 85° 

 can be considered as a straight line, the viscosity decreases to less 

 than half its original value (from 0,008 C.G.S. to 0,003 C.G.S.) ; 

 etc. Neither does the curvature of the x-^lines seem to be immediately 

 connected with the absolute value of the viscosity : with acetic acid, 

 whose viscosity is about three times, with salicylic aldehyde, whose 

 viscosity is four times, with pyridine, whose viscosity is about twice, 

 with phenetol. where it is circa three times as large as thai of 

 ethylalcohol, — in all these cases the curvature of the '/-^cwi'ves is 

 less than for the last mentioned liquid, because they are almost 

 straight lines ; and with the aniline and nitrobenzene, whose viscosity 

 is about eight or ten times as great, as that e.^. oi' \\ie ethylfonniate, 

 the /-^curves are even slightly convex. In many cases the "/-^-curves 

 will show a more rapid and steeper curvature at the higher tempe- 

 ratures, where the viscosity becomes smaller; and the part of the '/-^ 

 curve betw^een — 79° and 0° is often almost a straight line. With 

 the ethylalcohol the viscosity is about three times as great as in the 

 case of ethylacetate or ethylformiate, but notwithstanding that, the 

 /-^curves show in all three cases about the same curvature. 



To be sure, we have met during our measurements numerous 

 cases, wiiere xery clearly the impossibility was shown, to determine 

 the surface-energy mdependently of the viscosity. But this we 

 observed only, wdiere the viscosity reached such enoi'mous magnitude, 

 that the liquid became glassy or gelatineous, and did not or hardly 

 move on reversing the vessel. Such cases we found in : methyl- 

 cyanoacetate , methyl-methylacetyloacetate, diethylbromomalonate, die- 

 titylbenzylethylmalonate ; in undercooled dimethyl-, and die thy I tartrate 

 and a-campholenic acid, and ver}' strikingly with salol send resotxine- 

 monomethyl-, or dimethylethers. 



Even in these unfavourable cases we succeeded sometimes in 

 making some good measurements ; but in most cases this appears to 

 be impossible, which is shown by the fact, that even with so small 

 a velocity of formation of the gas-bubbles as 50 to more thaii 200 

 seconds, it proved to be impossible to tind a maximum pressure 

 H, which really is ^dependent of the speed of the nitrogen- 

 flow. 



