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 (2.5 grms.) is packed into the decomposition tube 15 mm. wide and 10 cm. high, and heated by an oil bath to a constant temperature, the oxides so produced are forced over ignited copper, where they are reduced, and the nitrogen retained in the measuring tubes.  Care must be taken that the acid decomposition products do not condense in any portion of the apparatus.  The air in the whole apparatus is first displaced by a stream of carbon dioxide issuing from a carbon dioxide generator, or gas-holder, and passing through scrubbers, and this stream of gas is maintained throughout the whole of the experiment, the gas being absorbed at the end of the system by strong solution of caustic potash.  To guard against the danger of explosions, which occasionally occur, the decomposition tube and oil bath are surrounded by a large casing with walls composed of iron plate and strong glass.

Dr Will’s apparatus has been modified by Dr Robertson,[A] of the Royal Gunpowder Factory, Waltham Abbey.  The form of the apparatus used by him is shown in Fig. 51.