EXPLOSIONS, BOILER, CAUSES AND PREVENTION OF. 



259 



ductors at the base of the globe, at which point 

 it is considerably thickened. The filament 

 rises above the middle of the globe and is 

 looped at the top. Edison prepares his carbon 

 filament from bamboo-fibers. It is held at its 

 extremities by small copper clips. The British 

 Electric Light Company exhibited a modifica- 

 tion of the Lane Fox lamp. The Maxim and 

 the Edison lights have been described in pre- 

 vious volumes. The material of Maxim's fila- 

 ment is cartridge-paper. Ihstead of produc- 

 ing a vacuum in the globe at once, he fills it 

 with a hydrocarbon gas, which deposits car- 

 bon on the hottest and therefore thinnest por- 

 tions of the thread, thus making it uniform in 

 strength and thickness. The Maxim lamps 

 have the advantage over the others that they 

 can be used with a powerful or a weak current 

 to produce either a bright or more moderate 

 light. By his ingenious generating apparatus 

 the strength of the current with which the 

 lamps are fed depends upon the number of 

 lamps, so that, if some of the lights in a circuit 

 are put out, the intensity of the remaining 

 ones is not increased. 



The International Congress of Electricians 

 settled upon a uniform international standard 

 of electrical measurement. The volt remains 

 the unit of electro-motive force, and retains its 

 old value. The ohm is also preserved as the 

 unit of resistance, and represents the same 

 quantity as before. The unit of current is the 

 same in value as before, being the current 

 given by one volt acting through one ohm's 

 resistance, although it is no longer called a 

 weber, but an ampere. The quantity of elec- 

 tricity transmitted per second by one ampere 

 of current is called a coulomb. The unit of 

 electrostatic capacity is the farad, which is so 

 related to the other measures that one cou- 

 lomb in a farad gives one volt ; in other 

 words, if a condenser be charged by an elec- 

 tro-motive force of one volt, it has as many 

 farads' capacity as it contains coulombs. 



EXPLOSIONS, BOILER, CAUSES AND PRE- 

 VENTION OF. The mystery that surrounds so 

 many boiler-explosions seems in a fair way of 

 being cleared up by the experiments of Mr. D. 

 T. Lawson, of Wellesville, Ohio, who in June, 

 1881, succeeded in exploding a boiler of the 

 best construction and well filled with water, 

 conditions which are generally held to secure 

 perfect safety. A number of explanations of 

 boiler-explosions have from time to time been 

 advanced by practical steam-users as well as 

 theorizers, but the commonly accepted ex- 

 planation the one held alike by steam-engi- 

 neers and the general public is the low-wa- 

 ter theory. According to this, an explosion is 

 due to the rapid conversion of the cool feed-wa- 

 ter into steam when it comes in contact with 

 the highly heated flues and other metal sur- 

 faces of the boiler left exposed to the fire. 

 When in contact with water these parts can not 

 become more highly heated than the water and 

 the steam above it, which is usually not much 



above 300 Fahr. ; but, if the water be allowed 

 to get low enough to uncover them, they may 

 readily be raised to a red heat (900 Fahr.). 

 If a fresh supply of water be then pumped into 

 the boiler, this, striking the hot iron, will be 

 quickly converted into steam, and it is held 

 that a sufficient pressure may be thus pro- 

 duced to cause an explosion. This theory was 

 pretty thoroughly tested some years ago by 

 a commission appointed by the United States' 

 Government, and provided with a liberal ap- 

 propriation. The experiments, which were 

 begun at Sandy Hook and continued near Pitts- 

 burg, resulted in failure, as the commission 

 was unable to produce an explosion, though a 

 great number of trials were made. No report 

 of the commission has been issued, the only 

 information accessible being the accounts in 

 the daily papers at the time. Mr. Lawson 

 takes issue with the low-water theory, on the 

 ground that but a small quantity of water 

 could be instantly converted into steam by 

 striking the hot iron of the boiler, and this 

 much too small a quantity to produce an ex- 

 plosion. "With a larger amount of water the 

 formation of steam would be too gradual to 

 produce the enormous and sudden pressure 

 necessary. In opposition to this theory he 

 advances the one that explosions are due to 

 highly heated water bursting into steam upon 

 the sudden removal of pressure from its sur- 

 face, and the then as sudden checking of the 

 escape of the steam so formed. This lessening 

 of pressure may be catistd either by the sud- 

 den withdrawal of steam to supply a cylinder, 

 as when ah engine is started ; or by suddenly 

 condensing the steam by allowing the enter- 

 ing, comparatively cool, feed-water to strike it. 

 When either of these things happens, the high- 

 ly heated water bursts into steam, which, hav- 

 ing no vent, subjects the boiler to a powerful 

 concussive shock, quite sufficient, Mr. Lawson 

 thinks, to rend it. According to this theory, 

 the force of the explosion not only increases 

 with the amount of water in the boiler, but a 

 considerable quantity is necessary to produce 

 an explosion at all. The results of the experi- 

 ment undertaken by Mr. Lawson to test this 

 theory seem to very fully confirm it, and it ap- 

 pears to be in entire harmony with what is 

 known on the subject. 



As is well understood, the power exerted by 

 an explosive agent is due simply to its rapid 

 conversion by combustion into gases occupy- 

 ing many times the volume of the substance. 

 Now, gunpowder when exploded occupies a 

 volume in the gaseous form but 300 times 

 that of the solid one, and nitro-glycerine but 

 900 times, while steam occupies at atmospheric 

 pressure nearly 1,700 times the volume of the 

 water from which it was generated. It is 

 evident, then, that if water could be converted 

 into steam instantaneously, it would form a 

 very powerful explosive. Instantaneous action 

 probably never occurs, but it is quite possible 

 that the conversion can take place with suf- 



