Page:Popular Science Monthly Volume 92.djvu/201

 Popuhir Science Monthly

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��How Floating Particles of Dust Cause a Fire

SPONTANEOUS combus- tion is caused, so the chemists tell us, by floating particles of coal dust or other inflammable material jostling and clashing against one an- other until the friction they set up raises their tempera- ture to the ignition point. If this explanation is correct, it would appear as if such fires could be prevented by perfect ventilation. Such, however, is not the case, for ventilation may ac- tually help to bring about fire by spon- taneous combustion. Air facilitates oxida- tion, really fanning the warm dust into a blaze. Keep air damp and quiet to avoid fire.

����A Clock with Works Encased in a Huge Log

EVERYBODY stops to look at a clock in the oflftces of the Manufacturer's Association, in Seattle. It is a curious time-piece, the works of which are encased in a hollowed section of a Douglas fir log, probably more than two hundred and twenty-five years old. The section of the log serves admirably as a dial for the clock, the numerals, show- ing plainly

The appearance of the clock is not its only claim to dis- tinction. Its size also warrants more than ordinary inter- est. The dial of the clock is more than three and one- half feet in diameter and the minute hand more than four feet in length.

���The clock works are contained in the hollowed section of a fir log more than two hundred and twenty-five years old

��The palace was con- structed of ice blocks cut and laid like blocks of stone

The cannon were also made of ice and were strong enough to fire off charges of real gunpowder

��Guns of Ice That Fired Real Powder

MORE than one hundred and seventy- five years ago some ingenious Russian workmen conceived the idea of constructing a building of solid ice in the city of St. Petersburg, now Petrograd. They erected the structure shown in the accompanying illustration. It was fifty feet long, sixteen feet wide and twenty feet high. Before the palace, they placed six cannon of the six-pounder size, and these too were made entirely of ice. They were turned on a lathe. The cannon were more than orna- ments. They could and did shoot actual charges of powder. Although the bore of the barrel was only four inches, the ice was sufficiently strong to withstand the force of an explo- sion of nearly two thousand grains of powder.

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