282 HAROLD L. ALLING 
readings at fixed intervals of time and then plotting the results 
with temperatures as ordinates and times as abscissas. A time- 
temperature curve is thus obtained which indicates the behavior 
of the mineral in a most direct way. So long as the substance is 
simply raised or lowered in temperature at a steady rate, this curve 
follows a smooth course; a departure from this smoothness indicates 
that there has been either an evolution or an absorption of heat 
within the specimen. Such a change in the shape of the curve 
indicates a change of state, either in phase, or in modification. 
Time-temperature curves are obtained for a binary system from 
specimens composed of the two constituents in varying amounts 
from 100 per cent of one to 100 per cent of the other. The con- 
struction of the equilibrium diagram from these time-temperature 
curves is illustrated in Figure 14. Five time-temperature curves 
are shown as partitions in the end of a box, numbered 1, 2, 3, 4, 
and 5. The critical points or places where the curves change in 
direction are indicated by A’, B, D, F, and H’. These mark the 
points where crystallization commences and A, C, G, and dH, 
indicate where the solidification is complete, if the specimen is 
allowed to cool. If, however, the specimen is reheated, it will 
theoretically at least pass through the identical behavior except in 
the reverse order. That is, the points A, C, G, and H are deter- 
mined by the initial melting, and the points A’B, D, F, and H’ 
by complete liquefaction. 
Now these time-temperature curves (partitions) enable us to 
construct the equilibrium diagram by projecting or drawing con- 
struction lines parallel with the base from the points already men- 
tioned back to the vertical plane, as is indicated in Figure 14. 
Removing the time-temperature curves, which are merely scaf- 
folding, the diagram remains as a conventional method of indi- 
cating the crystallization behavior of an isomorphous series, i.e., a 
series of solid solutions. 
In Figure 15 the opposite extreme of a binary system is shown. 
The diagram is constructed in the same manner, from the projec- 
tion of the critical points of a series of time-temperature curves. 
In this case the two components are completely insoluble in the 
solid state. It will be noticed that the upper line, A,B,£,, repre- 
