633 
1907-8.] Preparation of a Glass to Conduct Electricity. 
A glass of the composition — 
32 parts of sodium silicate, 
5 parts of borax, 
*8 part of lead oxide, 
2 part of sodium antimoniate, 
showed less action by acid, and besides conducting well it was colourless. 
This will be referred to later as glass No. 50. About twenty glasses were 
then made containing small quantities of caesium, lithium, rubidium, zinc 
sulphide, strontium, magnesium carbonate, barium chloride, and calcium 
phosphate; but there seemed no possibility of being able to add enough 
of any of these substances to reduce the action of acids without also 
seriously diminishing the conductivity. It was incidentally noticed that as 
much as 20 per cent, of strontium could be added without appreciably 
affecting the conductivity. The addition of pure silica, and also various 
proportions of lead, gave no more hopeful results. A trace of sodium anti- 
moniate effectively removed all colour from the glass. Plates containing 
a large proportion of alumina were very brilliant, but too brittle to be 
worked. In the course of the research it was seen that glass plates made 
of the original mixture resisted water and acid far better after they had 
stood exposed to the air for some months. 
Many of the earliest pieces were so good in this respect that at first it 
was thought to be due to the alumina or silica absorbed from the clay of 
the pots first used. A new T slab made of the original mixture and in a clay 
pot was nevertheless strongly attacked by water and acid, especially the latter, 
so that a change in the surface of the glass with age was looked for. It 
seemed that a freshly made pla^e attracted moisture from the atmosphere 
to a greater extent than was the case in an old plate, and a delicate means 
of detecting the presence of this film of water was devised for the purpose 
of watching the alteration of the surface with time. A rod of pure cadmium 
w T hen dipped into water resting upon an earth-connected sheet of platinum 
foil becomes negatively electrified, and if it be connected to two quadrants 
of an electrometer while the other two are to earth, a wide deflection may be 
obtained. Now if the cadmium rest upon a piece of dry ordinary glass 
moistened only at the point of contact, the electrical charges cancel, and 
there is of course no deflection. The conducting property of the new glass, 
however, makes it possible to detect the least moisture upon its surface by 
this means. 
The needle of the Dolezalek electrometer was charged to 200 volts and 
a quartz suspension chosen which gave 571 mms. deflection for one volt, 
