635 
1907-8.] Preparation of a Glass to Conduct Electricity. 
two days. After the fourth day it gave a deflection of only 10 mms. in 100 
seconds. It was very clearly shown, therefore, that the surface had been 
enormously improved. 
The curves Nos. 1, 2, 3, 4, 5 in fig. 2 show the relative degree of moisture 
upon the surface of the unboiled plate from time to time, and No. 6 represents 
the greatest deflection produced by the boiled piece during the same total 
interval. 
Fig. 2. 
A drop of HC1 (1 in 5) was then placed upon either half. The surface 
condition of the unboiled piece after one hour is shown in fig. 3; the 
surface of the boiled half was quite unaffected. It was clear, therefore, that 
the slow improvement with time detected by the electrical method was due 
to the removal of alkali from the surface, and that the subsequent increased 
power to resist water and acids was due to the preponderance of silica. It 
is not claimed, of course, that this glass so prepared and treated can compare 
with ordinary glass as regards withstanding the attack of moist air or acid, 
but experience shows that in the moderately dry atmosphere of a room the 
plates may be regarded as permanent. 
