Chemistry and Physics. 119 



ing 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 mix- 

 ture 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 am- 

 monia. When there is no fire present there is no sulphuric acid pres- 

 ent, as such ; but as soon as the heat rises, ammonia goes off, and sul- 

 phuric 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 extinguishing 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 outside 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 Jong 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 ; and other volatile base might do. lam 

 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 there are peculiar dangers ; but if a person was standing very 

 near the fire, the ammonia would in part be evaporated, and the acid 

 remaining would be enough to injure the fabric. There are however 

 cases, such as curtains, to which this could not apply, and where it 

 would be valuable. 



Sir William Burnet's liquid is chlorid of zinc : he uses it for preserv- 

 mg wood and canvas, and also for preventing fire. I am certainly sur- 

 prised that more use has not been made of it, being as far as 1 have 

 seen it, so efficient. I believe the manner in which the chlorid of zinc 

 acts is very similar to that of sulphuric acid, destroying the organic 

 Jitter on the approach oi heat, and rendering it incombustible. It can 

 •>e introduced into wood at a specific gravity of 2000, I believe; sul- 

 phate of ammonia cannot easily be used above 1200. By heating the 

 solution more may be attained. Sulphate of ammonia is cheap and 

 easily procured and used, not hurting anything with which it may come 

 m contact, and therefore more easily managed in households. 



The chlorid of zinc is said to unite with the fibre. This cannot be 

 said for the sulphate of ammonia. It would not, however, come from 



