70 SECTIONAL ADDRESSES. 
gentleman. A few subsidiary investigations, however, received atten- 
tion, one being the action of organic matter when heated under pressure, 
including the formation of coal and the origin of the bituminous materials 
found where igneous rocks are intrusive into coal seams or beds of shale 
rich in organic matter. The other was the action of carbonate of lime 
on ‘ silex.’ 
It is not quite clear what the ‘ silex ’ was, as Hall employs the term 
for the material of which his Wedgwood porcelain tubes were made, 
while others used it to designate precipitated silica and various siliceous 
minerals. Ifit were porcelain, Hall was experimenting with the system 
CaO-Al,O,-SiO, on which the beautiful researches of Rankin and 
Wright executed at the Geophysical Laboratory in Washington were 
published in 1915. This work may be taken as an example of the 
highest type of investigations of the class which Hall initiated. About 
7000 individual tests were made. The complete ternary diagram con- 
tains fourteen separate stability fields, each for a definite chemical com- 
pound. Some of these are well-known minerals such as cristobalite, 
tridymite, sillimanite, anorthite, but many are new compounds, or 
minerals under forms which do not occur in rocks (such as pseudo-wol- 
lastonite). In addition to the three components there are nine binary 
compounds; three are ternary, but of these only two are stable. 
Between the stability fields are thirty boundary lines, which show under 
what conditions two minerals may exist simultaneously in the presence 
of liquid melt of a definite composition. The fields meet three together, 
in twenty-one quintuple points, eight of which are ternary eutectics, 
while thirteen are transition points. The lowest temperature at which 
liquids appear is 1170°C.+ 5°; no possible mixture of these three 
substances is completely fused below that temperature. 
Many binary systems and quite a number of ternary systems have 
now been explored, some of them very fully. The seed which Hall 
planted is growing into a mighty tree. It is bearing fruit most precious 
to petrologists, mineralogists, and physical chemists. The conditions 
under which certain minerals can form in igneous melts are being 
gradually determined. But as yet the results appeal to the mineralo- 
gist and physical chemist rather than to the geologist. Quartz, 
tridymite, calcite, pyrites, corundum, and other common minerals of 
rocks have now had their stability conditions determined when they 
occur in dry fusions at atmospheric pressure in presence of a limited 
number of other substances. The accuracy of the determinations is 
marvellous, and has been confirmed in many cases by independent 
investigations along different lines. These researches are of even more 
value to the technologist than to the geologist. In the system above 
mentioned, for instance, there are only three or four minerals among 
the compounds determined in the melts. But the whole system and 
all its compounds have a bearing on practical problems. The three pure 
substances, for example, are well-known refractories: silica, alumina, 
and lime. Silica is the material of the quartz-glass industry ; alumina 
forms alundum, an abrasive and a valuable refractory, while the uses 
of lime are too many to mention. Silica brick-is principally quartz and 
tridymite with a little lime as a bond; ganister brick is mainly silica 
