III. On the relations between the viscosity (internal friction) of liquids and their chemical nature.—Part II

In the Bakerian Lecture for 1894 (‘Phil. Trans.,’ vol. 185 A, p. 397), we gave an account of our work on the viscosity of some seventy liquids at different temperatures between 0° and the ordinary boiling-point, and we discussed the interdependence of viscosity and chemical composition. Among the liquids dealt with on that occasion, there was no member of the important series of esters or ethereal salts, and, further, only one ether—ordinary ether or ethyl oxide—was included in the list. We therefore thought it desirable, in order to make the investigation more complete, to obtain data for members of these two classes of organic substances. The physico-chemical relationships previously established made such determinations of particular interest. Among the various connections traced between chemical constitution and viscosity, one of the most striking was the different effect which oxygen exerted upon viscosity according to the different modes in which it was assumed to be associated with other atoms in the molecule. The influence which could be ascribed to hydroxyl-oxygen differs to a most marked extent from that of carbonyl-oxygen, and, although only three cases were studied, it appeared that ether oxygen, or oxygen linked to two carbon atoms, had also a value which differed considerably from those of oxygen in other conditions. There was thus an additional reason for making observations on esters and ethers, since both contain ether-oxygen.