he gas from the regulator to the burner by a small brass tap (Fig. 2).
This tap forms an adjustable bye-pass, and thus a small flame can be kept
burning, even though the regulator be completely shut off. It is obvious
that the quantity of gas supplied through the bye-pass must always be less
than that required to maintain the desired temperature. This regulator,
placed in a beaker of water on a tripod, will maintain the temperature of
the water during four or five hours within 0.2 deg. C., and an air bath during
six weeks within 0.5 deg. C.

To sum up briefly the method of using the regulator:--Being filled with
mercury to about 1\2 inch below the T, attach the gas supply as in diagram
(Fig. 2), the brass tap being open, and the tube B unclosed by the
mercury. Allow the gas to completely expel the air in the apparatus. Push
down the tube A so that the end of B is well under the surface of the
mercury. Turn off the tap of the bye-pass until the smallest bead of flame
is visible. Raise A and B, and allow the temperature to rise until the
desired point is attained. Then push the tubes A and B slowly down until
the flame is just shut off. The regulator will then keep the temperature
at that point.

~Will's Test for Nitro-Cellulose.~--The principle of Dr W. Will's test[A]
may be briefly described as follows:--The regularity with which nitro-
cellulose decomposes under conditions admitting of the removal of the
products of decomposition immediately following their formation is a
measure of its stability. As decomposing agent a sufficiently high
temperature (135 deg. C.) is employed, the explosive being kept in a
constantly changing atmosphere of carbon dioxide, heated to the same
temperature: the oxides of nitrogen which result are swept over red-hot
copper, and are then reduced to nitrogen, and finally, the rates of
evolution of nitrogen are measured and compared. Dr Will considers that
the best definition and test of a stable nitro-cellulose is that it should
give off at a high temperature equal quantities of nitrogen in equal
times. For the purposes of manufacture, it is specially important that the
material should be purified to its limit, i.e., the point at which further
washing produces no further change in its speed of decomposition measured
in the manner described.

[Footnote A: W. Will, _Mitt. a. d. Centrallstelle f. Wissench. Techn.
Untersuchungen Nuo-Babelsberg Berlin_, 1902 [2], 5-24.]

The sample of gun-cotton