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XIV. On a Mode of rendering Substances incombustible. 

 By Robert Angus Smith, Ph.D.^ Manchester*. 



I HAVE often been surprised that, considering the number 

 of materials which will not burn and the small number 

 which do burn, we should be compelled to build houses so liable 

 without constant watchfulness to instantaneous destruction ; 

 that we should go also to sea in vessels made of a most com- 

 bustible substance filled with enormous fires, frequently under 

 the care of ignorant men. I think, therefore, I may be ex- 

 cused when 1 endeavour to add to a knowledge of the mode 

 of rendering substances incombustible, or the theory of the 

 mode to be sought after, even if the addition which I make be 

 but a very small one. 



Silicate of potash has been considered good. It is a soluble 

 glass which was expected to cover the fibre of cloth or wood, 

 and so protect it from heat. This does act to some extent, pro- 

 bably in the same manner as stones do when put into a fire of 

 wood or coal ; they take heat but give none, and are also bad 

 conductors. If silicate of potash remained as a glass, it would 

 act also by keeping out the air ; but this does not seem to be 

 the case, as it falls after a time to a powder. 



It struck me that the mode of preventing combustion was 

 not by protecting the wood from the fire merely, as heat must 

 cause combustible gaj^es to rise from wood, whether there be 

 incombustible substances mixed with it or not, and these gases 

 will force their way to the surface where there is no longer any 

 preventive to burning. My object then was to find a substance 

 which would render the wood unfit to burn, and would cause 

 it to give out gases which would not burn; so that whilst the 

 wood itself was being preserved, except where in contact with 

 the fire, the gases would assist in extinguishing the fire. 



I first tried phosphate of magnesia and ammonia, thinking 

 the ammonia given out would be of use in extinguishing the 

 fire; but this was of no value, as apiece of calico required to 

 be made quite stiff with it before it was rendered incombustible. 

 The calico was prepared by dipping in a solution of phosphate 

 of magnesia in muriatic acid and then in ammonia. It seemed 

 to me that the earthy salts are of little use for the purpose 

 required, and that the amount of solid matter incapable of 

 evaporation left on the cloth, assists in a very small degree. 



Sulphuric acid, however, seemed to present the most pro- 

 mising characteristics of a substance incapable of burning, and 

 of acting so strongly on vegetable substances as to make them 



• Comnuinicated by the Autlior,having been read before the Manchester 

 Literary and Philosophical Society, January 9, 1849. 



