300 Scientific Proceedings, Royal Dublin Socicty. 
The quartz here is obviously at a temperature considerably 
below that of the walls of the trough, seeing that this latter is 
open freely to radiation and convective cooling. 
Further experiments, using a platinum tube and stronger 
fibres, appeared to reveal slow extension at still lower tempera- 
tures, but the completion of these I have had to defer. 
Previous results have always placed the softening point of 
quartz at a much higher temperature ; the apparent melting point 
is, in fact, higher. Not till temperatures of between 1400° and 
1500° ©. are reached does fine quartz dust show any change 
appreciable in the time we ordinarily assign to observations of the 
kind. Mr. Ralph Cusack, working with a meldometer, gives its 
softening point at 1406° C. (“ On the Melting Points of Minerals,” 
Proc. Royal Irish Academy, 3rd ser., vol. iv., p. 399), and in my 
own previous observations I had fixed its softening point as only 
a little over 1400° C. (see Plate VI., “On the Determination of 
the Melting Points of Minerals,” Proc. Royal Irish Academy, 3rd 
ser., vol. ii., p. 38). Previously to these observations, it had been 
fixed as very much higher—above the melting point of platinum 
by some—that is, over 1750° C. 
Evidently the observations indicate that silica is a body 
possessing an extraordinary range of viscosity. It is a thick—a 
very thick—liquid at about 1500°C. At a temperature of about 
800° C. it is plastic, and yields with considerable rapidity to 
distorting forces. We may, perhaps, infer from the complete 
absence of cleavage that it is a substance which never crystallizes 
very vigorously. 
Let us now see if the oxides, entering as bases into the 
constitution of the silicate, possess similar properties. These 
are chiefly—alumina, lime, magnesia, soda, potash, and iron- 
oxides. 
Alumina.—According to M. Moissan (“Le Four Electrique,” 
Paris, 1897), when melted and again cooled, this substance rapidly 
crystallizes. The crystallization of small rubies (coloured with a 
little sesqui-oxide of chromium) is so rapid that 10 to15 minutes 
suffices for their formation. Crystals may also be obtained by 
sublimation. This, then, is evidently a body of very different 
properties from silica. It is a rapid and vigorous crystallizer from 
the state of fusion. 
