convenient than the lamp gallery. In tests with explosive mixtures,
after the device to be tested has been introduced and preparations are
completed, operations are controlled from a safe distance by a
switch-board in a building near-by.

Among other investigations conducted in this gallery are those of the
effect of sparks on known gas mixtures. These sparks are such as those
struck from a pick on flint, but in this case they are produced by
rubbing a rapidly revolving emery wheel against a steel file. The effect
of a spark produced by a short circuit of known voltage, the flame from
an arc lamp, etc., may also be studied in this gallery.


STRUCTURAL MATERIALS INVESTIGATIONS.

The structural materials investigations are being conducted for the
purpose of determining the nature and extent of the materials available
for use in the building and construction work of the Government, and how
these materials may be used most efficiently.

These investigations include:

(1).--Inquiries into the distribution and local availability, near each
of the building centers in the United States, of such materials as are
needed by the Government.

(2).--How these materials may be used most efficiently.

(3).--Their fire-resisting qualities and strength at different
temperatures.