MECHANICS AKD USEFUL ARTS. C7 



Among the effects of fine reduction of fnols, the e.xtraordinary 

 length and volume of the tlames generated is one of the most no- 

 ticeable. A jet of coal-dust and air, 4 inches in diameter, driven 

 into a hollow l>rick chamber with a velocity of G,0!jO fe(>t a minute, 

 will create a llame 3 or 4 feet in diameter and from 20 to 130 feet 

 long. These long flames are probably caused by the repeated 

 formation, decomposition, and reproduction of carbonic acid. 

 Minute particles of carbon float the entire length of the flame, and 

 serve at once to generate and to decompose the gas, producing- a 

 continued flame. 



ELECTRICITY VS. BOILER INCRUSTATION. 



. In the "Journal of the Franklin Institute," for February, 1868, 

 Dr. C. M. Cresson communicates an article on this interesting and 

 important subject. At the outset the electrical explanation wag 

 surrounded by so many popular errors and such conflicting vievi^s 

 on the nature of electricity, that the facts in the case were lost 

 sight of. Testimony of the strongest character having shown that 

 this agent does produce the effects claimed for it, Dr. Cresson of- 

 fers this answer to the question " how these results are produced." 



The api^aratus, in its simplest form, consists of a magnetic bar 

 of hardened steel, suspended horizontally within the steam boiler, 

 in the upper part of the steam space, the south pole connected with 

 the shell of the boiler, and the north pole supported by an insu- 

 lated hook. 



After explaining the relations of heat, electricity, and magnetism 

 to each other, and the modes of their conversion, on principles 

 announced by Farada}^ Grove, Prout, and others, with illustra- 

 tions of their action, he arrives at the following conclusions: — 



" 1. In a steam boiler, the thermal, and consequently the electri- 

 cal, currents flow alternatxdy toward and from the heated shell, 

 as induced by variations of the temperature of the different parts 

 of the shell and water, until some great disturbance of electrical 

 tension is made by taking oft' steam or water rapidly; when- in 

 order to restore the equilibrium of tension, electrical currents near 

 to the shell of the boiler flow constantly to it, as the metal is a 

 better conductor of electricity than water, carrving with them anv 

 matter that may be in solution or in suspension, and thus cause 

 formation of scale in compact columnar form. 



" 2. The thermo-electrical currents can be controlled b3"a suita- 

 ble magnetic force ; and therefore the magnets used in the boiler 

 direct the lines of thermo-electric action, and thus remove or 

 eideeble the causes of the compact deposition of bodies in solu- 

 tion or suspension in the water in the boiler. 



'* 3. Where scale has been formed previous to the application 

 of the magnets, it is repelled by the agenc}' of magnetic and dia- 

 magnetic forces, exerted in consequence of the polarity of the 

 shell of the boiler, induced by the movement of the thermo-elec- 

 tric currents, directed or governed b}^ the magnetic bar of the 

 instrument; which repulsion favors the intrusion of a minute 



