between the viscosity of liquids and their chemical nature. 573 
Conclusions draivn from the Graphical Representation of the Results. 
From the graphical representation of the results, we appear to be justified in 
assuming that the value of the viscosity coefficient depends not only on molecular 
weight and chemical constitution but also on molecular complexity. 
For liquids which probably contain simple molecules, or for which there is, in any 
case, little evidence of the association of gaseous molecules, the following conclusions 
may be drawn :— 
(1) In homologous series, or in series of related substances, the viscosity is greater 
the greater the molecular weight. 
(2) An iso-compound has always a smaller viscosity coefficient than the correspond¬ 
ing normal compound. 
(3) An allyl compound has in general a coefficient which is greater than that of 
the corresponding iso-propyl compound, but less than that of the normal propyl 
compound. 
(4) Substitution of halogen for hydrogen raises the viscosity by an amount which 
is greater the greater the atomic weight of the halogen. 
Successive substitution of hydrogen by chlorine in the same molecule brings about 
different Increments in the viscosity coefficient. 
(5) In some cases, as in those of the dichlorethanes, constitution exerts a marked 
influence on the viscosity; and in the case of the dibromides and benzene it may be 
so large that the compound of higher molecular weiglit has the smaller viscosity. 
(6) Certain liquids, which probably contain molecular complexes, do not obey these 
rules. Formic and acetic acids are exceptions to rule (l). The alcohols conform at 
some, but not at all, temperatures to rule (2); at no temperature, however, do they 
conform to rule (3). 
(7) Liquids containing molecular complexes have in general large values of dr}/clt. 
(8) In both classes of liquids the behaviour of the initial members of homologous 
series, such as formic acid and benzene, is in some cases exceptional when compared 
with that of higher homologues. 
Algebraic Kepresentation of Results. 
We have already discussed the various types of mathematical expression which 
have been suggested in order to represent the relation of viscosity to temperature. 
As already stated, we found that, on the whole, the most satisfactory formula hitherto 
devised is that due to Slotte. We, therefore, next sought to determine whether 
any connection could be traced between the magnitudes of the constants in this 
formula and the chemical nature of the substances. Writing the formula in the 
shape rj = C j {I + hty‘, where C is tjq, the viscosity coefficient at 0°, it is seen—as, 
indeed, follows from the previous discussion of the disposition of the curves—that, in 
general, in any series of related substances : 
