MECHANICS AND USEFUL ARTS. 85 



tive-power for their action. The metallic powder is container! in 

 a lar2;e reservoir, having a small oi'ifice at the bottom, through 

 which the powder falls simply by its own gravity, like sand in an 

 hour-glass. In order that a sufficient orifice may be used, and to 

 facilitate the steady flow of the powder, it is mixed with a quan- 

 tity of fine sand or other diluting material, the proportion of pow- 

 der to sand being varied according to the amount of light re- 

 quired. After leaving the orifice of the reservoir, the stream of 

 metallic powder and sand falls fi-eely through a metal tube, into 

 the upper end of which a small stream of ordinary gas is also 

 introduced. The mingled streams of powder and of gas thus flow 

 down the tube and escape together at its mouth, where they are 

 ignited, and continue burning with a brilliant flame as long as 

 the supply of gas and metal is maintained. As the metal becomes 

 consumed, the sand with which it was mixed falls harmless into 

 a receptacle provided for it, while the fumes are entirely carried 

 away by a small tube-chimney into the outer atmosphere. Im- 

 mediately below the orifice, there is a valve, to either regulate the 

 quantity, or entirely arrest the flow of the metallic powder, which 

 valve may be opened and shut at pleasure. When it is desired 

 to light the lamp, the gas is first turned on, just sufficiently to 

 produce a very small jet at the mouth of the tube, which small jet, 

 being once kindled, may be allowed to burn any convenient time, 

 until the moment the magnesium light is required. All that is 

 then needed is to turn on the metallic'powder, which instantly de- 

 scends and becomes ignited as it passes through the burning gas. 

 This action of turning on and off the metallic powder may be re- 

 peated, without putting out the gas, as often and as quickly as 

 desired ; so that, in addition to the ordinary purposes to which 

 lamps are applied, an instant or an intermittent light of gi-eat 

 brilliancy, suitable for signals or for light-houses, may be very 

 simply produced with certainty of eft'ect, and without the smallest 

 waste of metal. Mr. Larkin explained that the lamp could be 

 made to suspend from the roof, in place of an ordinary gas sun- 

 liglit, and arrangements could also be made for its use in signals 

 and for light-houses. The greatest difticulty was the price of tlie 

 metal ; but only about four years had elapsed since the produc- 

 tion of the metal in any quantity by Mr. Sonstadt, and the 

 demand for it hitherto had been a fancy one. Mr. Larkin said 

 that the cost of burning magnesium in the lamp Avhich he exhib- 

 ited would, at its present price, be about £1 an hour, and that no 

 difficulty whatever was experienced in reducing the magnesium 

 to powder. — British Association Report, 1866. 



PAKAFFIN FOR WATER-PROOFING. 



About three years ago. Dr. Stenhouse took out a patent for ren- 

 dering leather and various textile and felted fabrics water-proof, 

 by means of paraffin ; it was found, however, that paraffin alone, 

 especially when applied to fabi-ics, became, to a considerable ex- 

 tent, detached from the fibre of tlie cloth after a short time, owing 

 to its great tendency to crystallize. The presence, however, of 

 8 



