Vol. 7, 1921 
PHYSICS: E. W. WASHBURN 
115 
muscle has not been determined. A dye that I have made by linking 
novocaine with a benzene nucleus was found to be physiologically active, 
like the 2.5% novocaine, and appears to stain the elements acted upon by 
the novocaine. When the stain is diazotized directly into the living muscle, 
by putting the tissue first into novocaine and then into a solution of the 
staining base, only the muscle nuclei take the stain deeply, the nervous 
elements of the end-plates as well as the motor fibers remaining uncolored. 
It seems reasonably certain, therefore, that novocaine acts upon some 
constituent of the neuro-muscular mechanism beyond the end-plates. 
The significance of the affinity of the dye for the muscle nuclei is as yet 
unknown. The object of this note is to direct the attention of physiologists 
to a convenient substitute for curare. 
NOTE ON A METHOD OF DETERMINING THE DISTRIBUTION 
OF PORE SIZES IN A POROUS MATERIAL 
By Edward W. Washburn 
Department of Ceramic Engineering, University of Illinois 
Communicated by W. A. Noyes, February 12, 1921 
The pressure required to force mercury into a capillary pore of radius, 
2 y cos 6 
r, is , where y is the surface tension and 0 the angle of contact. 
r 
Upon this relation can be based a method for determining the effective 
pore diameters in a porous material such as charcoal. If pores of various 
diameters are present, one may determine also the fraction of the total 
porosity which is due to pores having effective diameters lying between 
any two stated limits. The procedure would be as follows: 
The coarsely granular sample of the thoroughly outgassed material is 
weighed and placed in a steel pressure bomb which is then evacuated 
until all adsorbed gases are removed. Pure mercury is then admitted to 
fill the bomb and a series of pressure and volume measurements are made 
at various pressures up to the highest pressure it is desired to employ. 
The decrease in volume, AV, accompanying a small pressure increase 
of Ap, in any part of the range must evidently be due to the filling of 
pores whose effective radii lie between the limits r and r — Ar, or 
Ar _ — 2y cos 0 
Ap p* 
A blank experiment without the porous material should of course be 
made in order to correct for the compressibility of the mercury and the 
expansion of the bomb under pressure. For accurate results the com- 
pressibility of the porous material, and the variation of y and 0 with p 
should also be known. 
