194 Mr. A. E. Dunstan on the Coefficient of 



series o£ papers on the viscosity of liquid mixtures, may be 

 briefly summarized in connexion with this work on alloys 

 (Dunstan, Chem. Soc. Journal, 1904, lxxxv. p. 817; 1905, 

 lxxxvii. p. 11; 1907, xci. p. 83). 



1. There is an intimate relationship for all substances 

 between the viscosity coefficient and the molecular condition. 



2. In the case of liquid mixtures of completely miscible 

 components, the viscosity concentration curves afford evidence 

 of the mutual effect of the one component on the other ; and 

 from observations of the tangential angles at each end of the 

 viscosity concentration curve, it is possible to obtain, firstly, 

 the relative molecular masses of the component liquids ; and, 

 secondly, evidence as to their dissociation on the oue hand, 

 and as to their homogeneous or heterogeneous association on 

 the other. 



3. Maxima in the viscosity concentration curves are found 

 at points of simple molecular composition (e. g. 1 alcohol 

 3 water), and are due to the associations of molecules of each 

 compound in simple ratios. 



1. Minima are also found at points of simple molecular 

 composition, and are due to the partial or ultimate fission of 

 one complex component by the other. 



5. For any chemical compound 



7} = A + B log as, 



where rj is the viscosity coefficient of the compound, A is a. 

 general constant for all substances, B is a specific constant 

 belonging to each family of closely related substances, and 

 x is the molecular weight of the compound. 



It is obvious, then, that an extension of this previous 

 work was desirable; and its application to the question of the- 

 molecular condition of the components of alloys was rendered 

 possible by Trouton's discovery of the relation described 

 above between viscosity as ordinarily defined and viscous 

 traction. 



In this preliminary paper, one of the simplest ranges of 

 alloys was chosen for testing the validity of the above con- 

 clusions on the variation of the coefficient of viscosity with 

 concentration. The lead and tin system was selected because 

 the metals are readily obtained in a pure condition, the alloys 

 can be conveniently made without any volatilization, and can 

 be easily drawn into uniform wires. The two metals, more- 

 over, are closely allied chemically, their melting-points lie 

 nearly together, and consequently there is little chance 

 of chemical union ; hence, we should expect that each 



