CHEMISTRY: W. D. HARKINS 
569 
THE ADHESION BETWEEN MERCURY, WATER, AND 
ORGANIC SUBSTANCES, AND THE FUNDAMENTAL 
PRINCIPLES OF FLOTATION 
By William D. Harkins 
Kent Chemical Laboratory, University of Chicago 
Communicated by W. A. Noyes, October 14, 1919 
The primary purpose of this investigation was to determine the effects 
of the molecular attraction at the surface of a metal, and to compare 
these effects with those of the surface of an oxygen compound such as 
water. Since the flotation process depends upon the preferential wetting 
and adhesion of gas films on metals, including the heavy sulphides, etc., 
on the one hand and silica and similar substances on the other, the 
general principles learned in connection with such a study, should be 
fundamental for the study of the process. I have been informed by 
Dr. E. C. Bingham that the adhesion between organic substances and 
metals is also fundamental with respect to the characteristics of 
lubricants. 
The equation of Dupre^ and that of Harkins, both of which are based 
on pure thermodynamics, give us the most accurate means for the study 
of the effects of molecular attraction at surfaces. The equation of 
Dupre gives the adhesional work done during the approach of 1 sq. cm. 
of one surface to meet the same area of the other. This is numerically 
equal to the work necessary to pull the two surfaces apart. The work 
of approach is also equal to the decrease of free surface energy ( — A7) 
during the process which is given by the equation 
Wa. = —A7 = 71 + 72 — 71, 2 
where 71 and 72 give the free energy of the two unlike surfaces before 
their approach, and 71,2 is the free energy of the interface. 
The equation of Harkins gives the total energy of approach (E^) and 
this may be called the total adhesional energy, as follows : 
Ea = - AEs = (71 ) + (72 +^2) - (71. 2 + k 2) 
where I represents the latent heat of the surface or interface in ergs per 
square centimeter. The total adhesional energy is closely related to 
the molecular surface attraction, while the adhesional work is the tensile 
force necessary to pull the two surfaces apart, integrated through the 
distance which they move during separation, but given a negative sign. 
