118 Scientific Intelligence. 



metallic surface ; and it appears that this reaction takes place with all 

 bodies which, when treated with nitric acid, do not furnish products of 

 oxydation, but another series of bodies that admit of carbonic acid 

 forming one of their constituent parts, since they at the same time give 



up an equivalent of water. 



22. On a Mode of rendering Substances incombustible ; by Robert 

 Angus Smith, Ph.D., Manchester, (Phil. Mag., xxxiv, 116, Feb., 

 1849.) — 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 watchful- 

 ness to instantaneous destruction ; that we should go also to sea in ves- 

 sels made of a most combustible substance filled with enormous fires, 

 frequently under the care of ignorant men. I think, therefore, I may 

 be excused when I endeavor 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, probably in the same man- 

 ner 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 re- 

 mained 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. 



Il struck me that the mode of preventing combustion was not by pro- 

 tecting the wood from the fire merely, as heat must cause combustible 

 gases to rise from wood, whether there be incombustible substances 

 mixed with it or not, and these gases will force their way to the sur- 

 face 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 con- 



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



I first tried phosphate of magnesia and ammonia, thinking the am- 

 monia given out would be of use in extinguishing the fire ; but this was 

 of no value, as a piece of calico required to be made quite stiff with it 

 before it was rendered incombustible. The calico was prepared by 

 dipping it 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 inca- 

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



Sulphuric acid, however, seemed to present the most promising char- 

 acteristics of a substance incapable of burning, and of acting so strongly 

 on vegetable substances as to make them incapable of burning. Sul- 

 phuric acid itself is a body perfectly burnt, or we may say overburnt, 

 having an atom of oxygen given to it by artificial means, so to speak, 

 which atom is difficult to separate, and therefore not resembling the 

 oxygen of many highly oxydized bodies. It requires a high degree of 

 heat to raise it to vapor; and the vapor formed is sluggish and heavy* 

 remaining long where formed, and quenching flame wherever it is. It 

 destroys the texture of wood also and other vegetable substances, caus- 



