BETWEEN THE VISCOSITY OF LIQUIDS AND THEIR CHEMICAL NATURE. 93 
then the curves for its next higher homologues, the isomers methyl acetate and ethyl 
formate ; then come the curves for the next higher homologues, the isomers ethyl 
acetate, methyl propionate, and propyl formate ; and, lastly, the curves for the next 
higher isomeric homologues methyl isobutyrate, ethyl propionate, methyl butyrate, 
and propyl acetate. Passing to the relative position of the curves for isomeric esters, 
it is noticeable that, where the comparison is possible, the formate has at any tem¬ 
perature, the largest viscosity-coefficient. The curvm for ethyl formate lies to the 
right of that for methyl formate, and the curve for propyl formate is far to the right 
of those for ethyl acetate and methyl propionate; indeed, at low temperatures it 
Fig. 1. 
almost coincides, and at liigh temperatures it actually coincides, with the curve of its 
higher homologue, methyl isobutyrate. It is more than likely that the large viscosity- 
coefficients of the formates ai’e associated with the fact, previously established, that 
of the five lowest fatty acids, formic acid has, at low temperatures, the largest 
coefficients, and that these coefficients are larger than the}^ might be expected to be 
even on making allowance for molecular aggregation. 
On comparing the isomeric propionates and acetates, it is seen that although the 
curve for ethyl acetate is very slightly to the left of that for methyl propionate, the 
curve for propyl acetate is far to the right of that for ethyl propionate. This is 
the result of the influence exerted by the symmetry of the molecule in lowering 
the viscosity. In the first case the acetate is a symmetrical compound and the 
propionate is unsymmetrical; in the second case both compounds are unsymmetrical. 
In conformity with the general rule, the curve for methyl isobutyrate lies well to the 
