PROCEEDINGS 
OF THE 
NATIONAL ACADEMY OF SCIENCES 
Volume 7 MAY 15, 1921 Number 5 
THE DIFFUSION OF AIR THROUGH WATER IN THE LAPSE OF 
YEARS 1 
By Carl Barus 
Department of Physics, Brown University 
Communicated January 10, 1921 
In 1912 I put up a U-tube of the form annexed, containing a charge 
of water, ww', below the air chambers, aa' , both at nearly atmospheric 
pressure. The tubes were sealed by fusion cautiously, to avoid the pres- 
ence of flame faces in aa r . They were then put away in a dark vault 
of nearly constant temperature, for short time ranges, to be examined from 
time to time as to the displacement of the thread of water within: for it 
will be seen that the meniscus under a' is at a pressure excess of hpg as 
compared with the meniscus under a. If L is the total length of the thread 
of liquid in the tube, we may define the coefficient (k) of diffusion (by 
volume) by the equation 
v = icat(hpg)/L 
where v is the volume diffusing at nearly constant mean pressure in the 
time t through an area a, the density of liquid 
being p = 1. Hence, 
v L _ 1 dh L 
at hpg 2 dt hpg 
where dh/dt is the loss of head per second. The 
factor yi appears since the volume lost at a' ap- 
pears at a, and their sum is equivalent to the loss 
of head. The amount of diffusion is so small that 
corrections may be disregarded. 
The observations made before the spring of 
1914 were not satisfactory because of deficiencies 
of method. They were, therefore, discarded. 
Measurement was thereafter made with the cath- 
133 
