J oLy— The Order of Formation of Silicates in Igneous Rocks. 299 
I have lately found that the softening point of quartz is far 
below what is currently thought. My experiments on this point 
were carried out in the following manner :— 
A. quartz fibre was stretched horizontally, fixed at one end, 
and at the other a tensile force was applied. This was produced 
by causing the fibre to displace from the vertical a pendulum 
carrying a small mass as its bob. 
For 10 cms. of its length, this fibre traversed an open trough 
of platinum foil—square in section and 0-10 x 0-15 cms. in 
dimensions. This trough, being arranged so that it replaced the 
ribbon of a meldometer, could be heated to any required degree by 
a current, and its temperature determined by its thermal expansion. 
The fibre was so placed in the trough as to be depressed somewhat 
below the axis or central line of the latter. 
Two micrometer microscopes observed points on the fibre 
(obtained by wetting a short length of it with varnish and 
dusting charcoal powder upon it) placed well to right and left of 
the heated portion. The displacement of the point on the cross 
wires of the right-hand micrometer measured the extension; the 
micrometer to the left of the trough served merely to safeguard 
against unnoticed displacement occurring at the fixed extremity of 
the fibre. 
The data are :— 
Force, . : : 0°425 grams. 
Length heated, . 10 cms. 
Diameter of fibre, . 0:00136 ems. 
Cross-section of fibre, 0°145 x 10° cms. 
Stress, : . 293 x 10° kilogrames per sqr. cm. 
Temp. of trough, . 850° C. 
Under these conditions one set of observations gave— 
In 55 minutes extension = 0:076 cms. 
In next 35 ,, ae = 0089 5, 
Many other observations were made at this temperature. The 
extension continually progressed: finally the fibre broke when 
cooling the trough. I may observe here that the stress applied is 
about 5th the minimum carrying power of quartz fibre. 
