DIFFUSION IN SILICATE MELTS 301 
EXPERIMENT NO. 21 
Depth of diopside layer 3.9 mm. Total deptho.1 mm. Time 22 hrs. 
Distance from bottom 
(mm )is ess cas On IOC HON A TOMS On OFOMm HOM OnOn ms OnS 
Vol. per cent diopside.. 48.0 47.9 47-5 45-5 43-0 41.0 36.5 30.5 29.5 
Plagioclase of upper layer Ab,An,. 
Immersed in bath of molten gold. 
EXPERIMENT NO. 37 . 
Depth of diopside layer 7 mm. Total depth 10.2 mm. Time 17 hrs. 
Distance from bottom 
(Gani) aoe oiee Sree Qi wen ar lee oye: 
-7 
6.3 
Vol. per cent diopside. 73.0 72.8 72.3 70.5 70 8.8 
7 
6 66. 
Plagioclase of upper layer Ab,;An,. 
EXPERIMENT NO. 25 
Depth of diopside layer 3.2 mm. Total depth 14.5 mm. Time 22.5 hrs. 
Distance from bottom 
Grinie eee rol ahe3 ON 3) 07/43) 6-3) O23 1Os3 PL .3) L223) 13h3 14-2 
Vol. per cent diop- 
Bide 4215 30-3) 301.320.924.420. 3 20.1 17.8172) 15-0 14.6) 0.5, ©.0 71-3 
Plagioclase of upper layer Ab;Anz. 
Figures 1-5, in which the ordinates represent height in millimeters 
above the bottom and the abscissae composition in units per cent 
of diopside. The initial condition will then be represented by 
two vertical lines indicating two uniform layers, one at 100 per cent 
diopside and of a length corresponding to the depth of the diopside 
layer, the other at o per cent diopside representing the layer of 
plagioclase above it and of appropriate length. These are joined 
by a horizontal line indicating instantaneous change of com- 
position. The final condition will be represented by a curve on 
which any point represents the composition at the corresponding 
level. The slope at any point indicates the composition gradient 
at that point, the curve approaching more nearly to the horizontal 
the greater the composition gradient. The figures need little 
discussion since they present the results better than can be done 
in words. 
THEORETICAL CONSIDERATIONS 
As noted on an earlier page, concentrations in a mass under- 
going diffusion may be calculated on the basis of Fick’s law. In 
its application to the present case, and in the form most useful for 
