Popuhir Science Monthly 



185 



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 Tliat 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. 



