300 N. L. BOWEN 
Though numerous measurements were made by the early, 
rougher method, only the few made by the later method will be 
described. It may be noted, however, that the earlier results, 
within their rather large limits of error, agree with the later. 
In order to obtain a visual impression of the diffusion of material, 
such as is obtained when copper sulphate crystals are placed in the 
bottom of a vessel of water, the layer of diopside was in some 
cases colored by the addition of 1 per cent Fe,O, which imparts 
to the glass a marked green color. In all cases the change of 
color was sensibly coincident with the change of refractive index; 
in a layer where the index fell rapidly the color faded rapidly; 
in cases where an upper layer was found unaffected in refraction 
it was likewise uncolored.* 
In summary it may be stated that the mode of procedure was 
as follows: A layer of diopside was placed in the bottom of a 
crucible with a layer of plagioclase above it, diffusion was per- 
mitted at constant temperature (above the melting-temperature 
of both layers) for a definite period, the charge was quenched, 
and the composition determined at various depths by measuring 
the refractive index of the glass. 
GRAPHICAL PRESENTATION OF RESULTS 
The results (Table I) may be presented graphically as in 
TABLE I 
DIFFUSION RESULTS 
EXPERIMENT NO. 24 
Depth of diopside layer 1.8 mm. Total deptho.5 mm. Time 48 hrs. 
Distance from bottom 
(amma) eects Oo8 Wok set eth chs} 
nN Oro§ ° 
2 13 853 “ORS 
Vol. per cent diopside. 39.5 39.6 38. ih it 
5-3) (O-3iees 
7.5) Anommses ° 
Plagioclase of upper layer AbzAny. 
EXPERIMENT NO. 27 
Depth of diopside layer 3.2 mm. Total depth 11.7 mm. Time 48 hrs. 
Distance from bottom 
(oan) Peer ese I.0 2.0 3.0 4:0 5.0 6.0 7:0 S:0mG.OMtonomsamem 
Vol. per cent diopside.52.0 51.6 50.7 49.6 46.5 33-7 9.7 2-4 0.7 ° ° 
Plagioclase of upper layer Ab2An,. 
«This result might be taken as indicating that selective diffusion was unimpor- 
tant, though not necessarily absolutely lacking. 
