Page:Proceedings of the Royal Society of London Vol 60.djvu/168

Rh the relation between viscosity in absolute measure and temperature are calculated for each liquid. The general results of the observations are then discussed in the same manner as in the previous memoir. With regard to the two hydrocarbons, it is found that the isopentane from fusel oil gives slightly different values from that originally observed, which was obtained from American petroleum, and which, although of an approximately constant boiling point, was undoubtedly a mixture. The new sample of ethylbenzene, however, gave results which were in very good agreement with those previously obtained.

The conclusions relating to the graphical representation of the results may be thus summarised. Both ethers and esters give no evidence of molecular aggregation, and conform to the rules th at:—

(1) In homologous series, the viscosity is greater the greater the molecular weight. (2) An iso-compound has a smaller viscosity than a normal isomer. (3) The more symmetrical the molecule of an isomeric compound the lower is the viscosity. As regards the esters themselves, it is noteworthy, where the comparison is possible, th at:— (4) Of isomeric esters, the formate has the larger viscosity.

As regards the algebraical representation of the results, it is shown that in the expression rj = 0/(1 + ft1 + 7^), derived from Slotte’s formula:—

(1) In any homologous series, /3 and 7 increase as the molecular weight increases. (2) Of isomeric compounds, the iso-compound has the smallest coefficient. (3) Ethyl ether, the symmetrical isomer, has smaller coefficients than methyl propyl ether. (4) As regards normal isomeric esters, the formate has the largest, and the propionate the smallest coefficients, and the values of the acetate are larger than of the butyrate.

The authors then deal with the relationships existing between the various viscosity magnitudes—the viscosity coefficient, the molecular viscosity, and the molecular viscosity work—(1) at the boiling point, and (2) at temperatures of equal slope, the slope adopted being that employed in their previous paper, namely, 0,04323, and values for the oxygen in three .different conditions are given for each system of comparison in the same manner as in their first communication.

The two main results supported by all the methods of comparison, both at the boiling point and at temperatures of equal slope, are :—