atmosphere are the most likely conditions to produce trouble for the pyrotechnist, although whether the primary cause is heat or owing to an electrical condition of the atmosphere it is difficult to say, probably it is the two conditions in conjunction. Sulphur and shellac, two very important ingredients in the art, are both capable of holding an electric charge, and it seems not unlikely that they may be so charged in an electric atmosphere during the process of mixing.
Accidents in Class II are generally less easily explained than those in the former class and have occurred in many forms. As has been said, during the period (about sixty-five years) from the introduction of chlorate of potash to the Order in Council forbidding its use with sulphur, numerous accidents occurred; spontaneous ignition, both whilst drying during manufacture and even during mixing, ignition from very slight friction, and for a time a frequent occurrence the detonation of the contents of shell by the lifting charge. During the period of seventeen years between the date of the Explosives Act and the prohibition of chlorate sulphur mixture, twenty-eight accidents are recorded, resulting in eleven deaths attributable to the use of such mixtures.
The instability of chlorate sulphur compositions, however, does not appear to be so much due to the presence of these two chemicals themselves, but rather to the presence of impurity in conjunction with them.
Commercial sulphur often contains free sulphurous acid, which acting upon the chlorate produces chlorine tetroxide, which rapidly decomposes and ignites the mass of the composition.
Other acids which produce decomposition of the chlorate are equally likely to produce ignition. Of such cases, examples may be mentioned of acid being present in the paste used for case and box-making, also in gumwater which has been kept
