406 
MESSRS. T. E. THORPE AND J. W. RODGER ON THE RELATIONS 
alcohol C 3 B[:j(OH), propylene glycol C 3 He(OH) 3 , and glycerin 03115 ( 013 ) 3 . Indeed, 
the high viscosity of solutions of carbohydrates, e.g., the sugars, gums, &c., is probably 
dependent on the relatively numerous hydroxyl groups present in the molecule. The 
manner in which the hydroxyl group is combined seems, however, to have considerable 
influence on the viscosity. Thus, in the cases of the isomeric substances, benzyl 
alcohol and metacresol, it is found that, in the first-named substance, in which the 
hydroxyl group occurs in the side chain, the viscosity is very much less than that of 
the second, in which the hydroxyl group is attached to a carbon atom in the benzene 
ring. 
The foregoing observations practically include all that may be regarded as attempts 
to determine the connection between the viscosity and the chemical nature of 
homogeneous liquids. A very large amount of experimental work has been done, 
especially in the physical laboratories of Oscar E. Meyer, Wiedemann, and 
OsTWALD, on saline solutions and mixtures, in order to trace analogies and relations 
between viscosity and electric conductivity, temperature, concentration, &c.; but while 
these researches have been of great service in regard to the applicability and value of 
observational methods, they have added little to our knowledge of the special 
question with which we are more immediately concerned. 
Although it is manifest from the foregoing account that relationships do exist 
between the chemical character of liquid substances and that property which is 
related to their times of transpiration, it must be admitted that these relationships 
are not very precisely defined by such experimental evidence as we have at 
present. Instances have been given in which the results of different observers, and 
in some cases even those of the same observer, differ among themselves by amounts 
which cannot be reasonably attributed to imperfections in the principle of the 
methods employed. As a general rule, the plan adopted seems to have been to make 
relatively rough observations on as many liquids as could be obtained, rather than to 
institute a careful and systematic comparison between a few of well established 
purity. Moreover, the nature of the conditions by which truly comparable results 
could alone be obtained, has received but scant consideration. For example, it seems 
futile to expect that any definite stoichiometric relations should become evident by 
comparing observations taken at the same temperature. A few attempts have been 
]nade to ascertain the influence of temperature on the time of transpiratioji, but these 
are insufficient both in number and temperature range to admit of a trustworthy 
deduction of the'law of the variation. It seemed obvious therefore that in order to 
investigate the subject with reasonable hope of discovering stoichiometric relations> 
one essential point was to ascertain more precisely the influence of temperature on 
viscosity, and then to compare the results under conditions which have been found to 
be suitable in similar investigations in chemical physics. 
