Processes in the Useful Arts. 335 



upon trial, that when single rods were made to approach a flame, the lat- 

 ter was always inflected on all sides from the rod, as if repelled by it, and 

 that this effect was independent of the conducting power of the rod, whe- 

 ther good or bad. The amount of inflection or repulsion was directly as 

 the mass, and inversely as the distance from the flame. It was not dimi- 

 nished by increasing the temperature of the rod, even to such a degree as 

 to render it scarcely possible for it to abstract any of the caloric. In fact, 

 when two flames are made to approach each other, there is a mutual re- 

 pulsion, although their proximity increases the temperature of each instead 

 of diminishing it. 



" From these principles/' says the author, " the theory of the safety 

 lamp is easily deduced. A metallic wire, exerting, according to its diame- 

 ter and its own nature, a constant repulsion upon flame, it is evident that 

 two parallel wires, so near each other as not to exceed the distance of twice 

 the radius of the sphere of repulsion, will not permit a flame to insinuate 

 itself between them, unless it be impelled by a force superior to the inten- 

 sity of repulsion. If to these two wires others be added, a tissue is formed 

 impenetrable to flame, especially when the conducting power of the wires 

 adds its influence to that of the repulsion." 



The author conceives, that, from the views above stated, the number of 

 cross or horizontal wires in the Davy lamp is unnecessarily large, and that 

 by rejecting all of these excepting a number sufficient to secure the firm- 

 ness of the tissue, the lamp would afford as great a security as at present, 

 and at the same time diffuse a much greater light. This opinion he has 

 verified by actual experiment. — Bibliotheque Universelle de Geneve y Mars, 

 1827. 



5. Protection against Damp, Rust, &;c. By John Murray, F S. A. 

 F. L. S. &c. Communicated by the Author. 



I find that if linen or woollen cloth be immersed in water, saturated 

 with quick-lime and sulphate of soda, and then carefully dried, delicate 

 steel instruments folded up in it, even if themselves damp, are effectually 

 preserved from rust or oxidation. The rust of iron is found to contain a 

 carbonate of that metal, and the aqueous particles of " wet" and "damp* 

 are, it is proved, decomposed by the contact of iron at all temperatures, and 

 with increased effect at an elevated one, hence the formation of rust or 

 oxidation, &c. It is probable that the caustic lime not merely absorbs 

 any minute quantity of carbonic acid present in the air, and by damp 

 brought into more immediate contact with the iron or steel, but also absorbs 

 the first portions of present damp, perhaps too caustic lime may even 

 take up oxygen. 



The efflorescent sulphate of soda does not attract humidity, but rather 

 casts it off even its own water of crystallization. 



It is evident that an envelope of cotton or woollen cloth, saturated as 

 described, would not only be a protection against damp in the case of steel, 

 plate, &c. but also of equal value for the preservation of deeds, &c. whether 

 on paper or parchment. 



