BETWEEN THE VISCOSITY OF LIQUIDS AND THEIR CHEMICAL NATURE. 611 
1. It will be seen from the first table that, in the case of forty-five liquids, the 
difference between the observed and calculated values rarely exceeds 5 per cent. 
Here molecular weight and chemical constitution exert effects upon the magnitude 
of the molecular viscosity which can be quantitatively expressed with moderate 
exactness. 
In the case of the isomeric ketones and aromatic hydrocarbons the differences are 
in part due to constitutive influences which, as yet, on account of lack of data it is 
not possible to allow for in obtaining the calculated values. 
2, In the second table are found those substances which give differences exceeding 
this 5 per cent, limit. These may be roughly classed as unsaturated hydrocarbons, 
polyhalogen compounds, formic and acetic acids, benzene, water, and the alcohols. 
In many cases the differences are the result of constitutive influences. The same 
calculated value is used for ethylidene and ethylene dichloride. The large difference 
given by the latter is the result of the difference in the structure of the two com¬ 
pounds. The calculated values for the chlorraethanes are obtained by means of the: 
value possessed by chlorine in monochlorides. The differences are seen to increase as 
chlorine accumulates in the molecule, pointing to the conclusion, supported by other 
physico-chemical comparisons, that the effect produced on substituting hydrogen by 
halogen depends on the number of hydrogen atoms previously substituted. In 
calculating the value of carbon bisulphide, the value of sulphur in alkyl sulphides 
was employed. The large difference may be attributed, in part at least, to the 
difference in the mode of linkage of sulphur in the bisulphide. Benzene gives a 
large difference, probably for the reasons given when discussing the graphical 
representation of the results. 
The calculated value of aldehyde is obtained in the same way as that of a ketone. 
The difference obtained is, therefore, an indication of the generic difference in the 
chemical constitution of the two classes of substances. 
The calculated values of all the hydroxyl compounds given in the table are obtained 
by means of the constant for hydroxyl oxygen deduced from the higher fatty acids. 
It will be seen that in the case of the lower acids, of water, and of all the alcohols 
but methyl alcohol, there is no indication of agreement. For the lowest acid 
chemical constitution, as already mentioned, may in part be the cause of the 
difference, but for the other substances difference in molecular complexity at the 
boiling-point is doubtless the main factor in producing the large divergences above 
obtained. 
As the stoichiometric relationships exhibited by molecular viscosity at the boiling- 
point are on the whole not very definite, we do not intend to further discuss the 
results given in the above tables. 
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