On a Mode qfrendermg Substances incombustible. 117 



incapable of burning. Sulphuric 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 dif- 

 ficult to separate, and therefore not resembling the oxygen of 

 many highly oxidized bodies. It requires a high degree of 

 heat to raise it to vapour; and the vapour 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, causing them to give out after a time 

 gases which do not burn, mixed with some which do burn; 

 but if there be enough of acid, forming a mixture which does 

 not burn. The wood also cannot be again induced to become 

 combustible until it be heated to redness, so as to remove all 

 the sulphuric acid, leaving only charcoal. 



If sulphuric acid then could be introduced into wood just 

 at the time that the fire was going to take place, the fire would 

 cease to take place ; and this we can do easily by saturating 

 the wood with sulphate of ammonia. When there is no fire 

 present there is no sulphuric acid present, as such ; but as 

 soon as the heat rises, ammonia goes off, and sulphuric acid 

 is instantly presented to the wood. The ammonia does not 

 come off quite pure, it is mixed with nitrogen and sulphurous 

 acid ; and this disengagement of gases is of advantage in ex- 

 tinguishing fire; when the heat rises to 536°, the sulphuric 

 acid is then left to act on the wood in part and to volatilize in 

 part, and that which I have mentioned takes place. The out- 

 side of course would first undergo the change, and the inside 

 would be protected by the incombustible outer part ; if the fire 

 continued to act long, the inner layer would undergo a similar 

 change. I imagine, then, the acid acts in a double manner ; 

 it makes the wood refuse to burn and it puts out fire. As 

 sulphurous acid is given off in this process, the action is also 

 similar in one point of view to that of sulphur, which has 

 long been used for putting out fire in chimneys. 



I have no doubt that a house built of wood prepared in this 

 manner might have a fire lighted on the wooden floor without 

 danger, burning only on the spot to which the fire was limited. 

 A ship also would be safe, even if the cinders did fall from 

 the grate in stormy weather. 



1 know that muriate of ammonia has been used, and that 

 it acts very well ; but I think the sulphuric acid is superior, 

 the ammonia being merely to keep it innocent ; any other vo- 

 latile base might do. I am sorry, however, that this is not 

 perfect; its solubility in water is a great disadvantage, as it 

 cannot be applied to clothes to be frequently washed. True, 

 it is so cheap that it might be applied every washing where 



