Protection of Persons from Fire. 99 



inflammable substances in contact with it, on the side opposite to that 

 of the heating source. This is the principle of safety in the Davy 

 lamp, now so extensively used by miners. It is now, we believe, 

 generally admitted by chemists, that the effect of metallic gauze is to 

 be ascribed to the repulsion of the flame by the metal,* rather than to 

 the conducting power of the latter. The flame is thus prevented 

 from coming into contact vvith the wire. The author partakes of this 

 opinion, and he has proved that a gauze of amianthus produces a simi- 

 lar effect on flame. This appears to be the only substance of which, 

 without preparation, a tissue can be made suitable for resisting flame. 

 It is true that cotton and linen cloth, well impregnated with certain 

 saline solutions, are rendered almost incombustible. Sulphate of alu- 

 mina, carbonate of magnesia, and other salts, have this property ; but 

 none, according to Gay-Lussac, are equal to phosphate of ammonia. 

 When a cloth well prepared with this salt is exposed to the fire, the 

 salt melts, the ammonia is volatilized, and the vitrified phosphoric 

 acid forms around the tissue a varnish which defends it from combus- 

 tion. The cloth becomes ignited, but preserves its form and remains 

 simply carbonized. 



Chap. II. — On the art of preparing amianthus, and rendering it fit 

 for spinning and iveaving. 



No substance, artificially prepared, resists the action of heat so 

 well as amianthus, a property conferred upon it by nature. The 

 Romans made much use of this material, and appear to have been 

 well acquainted with the means of preparing it, fliough Pliny and 

 others consider it as very difficult to work. The author finds that it 

 is only amianthus of a certain consistence that is fit for use. It is of- 

 ten very white and shining, but too fragile. It sometimes contains 

 lumps, which cause the fibres to be too short for spinning. 



When taken from the mine, it contains generally portions of earth 

 or other foreign matters, which must be separated by putting it into 

 large basins full of water, where it should be left several days, sim- 

 ply renewing the water from time to time as it becomes charged with 

 earthy or other particles. Hot water is preferable to cold, and it is 

 of advantage sometimes to boil it either in pure water or in the lye 

 of ashes. The author has tried weak muriatic acid, and other chem- 



* The metal in Uiis case, but the gases which are evolved IVoiii flame, will, by 

 striking against anj- substance, cause a repulsion of the flame. 



