K. DOMESTIC AND HOUSEHOLD ECONOMY. 429 



box, into which is drawn all the fine and light flour dust, 

 thereby keeping the general air of the mill more free from 

 the flour dust floating in the air. Within the exhaust box is, 

 therefore, always found a very dusty atmosphere. Now when 

 a light is introduced into an atmosphere of flour dust, the 

 fine division of the flour so facilitates its rapid combustion 

 that the flour is resolved into 2;ases whose volume is much in- 

 creased by the high temperature, so that a veritable explosion 

 takes place, which explosion is most powerful when a certain 

 volume of the gas is mingled with a larger proportion of air. 

 In order that the explosion may be destructive, it is necessary 

 that the dusty atmosphere be more or less closely confined 

 within a given space. The most common cause of a spark or 

 flame in the flour-mill is by the running of the feed ofl" the 

 stones, whereby the stones come down against each other, 

 and quickly strike fire and become very hot. A very slight 

 obstruction in the pipe is sufticient to so diminish the supply 

 of grain as to allow the stones to come in contact with each 

 other. Sometimes, again, a nail or a stone goes down with 

 the feed, and causes sparks of fire to be struck ofl". Several 

 occasions are recorded in which a crackling: noise as of a run- 

 ning fire has been distinctly heard in the conduits leading 

 from the stones to the exhaust pan. These slight explosions 

 often blow open the fan box. If the flame passes the fan, 

 however, and gets into the exhaust box, every thing depends 

 upon the momentary condition of the air in the exhaust box 

 at the time, as to whether the explosion shall end there, or the 

 mill itself be blown up. The precautions to be taken in order 

 to avoid all mill fire explosions consist specially in removing 

 the exhaust box, stive rooms, smut rooms, and other recepta- 

 cles of flour dust, to the outside of the mill. Still better is 

 it if the conduits be provided with sliding or hinged valves 

 which would close at once if an explosion occurs in any of 

 the dust receptacles. Numerous other valuable suggestions 

 are contained in Dr. McAdams's paper. Transactions of the 

 Royal Scottish Society of Arts, IX., 42. 



TYRIAN-PURPLE INK FOR MARKING LINEN. 



Von Bele gives the following method for preparing an ink 

 for markino; linen and cotton : Neutralize 75 irrains of car- 

 bonate of ammonia with pure nitric acid, and triturate 45 to 



