OXALIC ACID. 73 



129. We frequently see on the top of charcoal or 

 coke fires a pale blue flame, quite different in appear- 

 ance from the usual bright flame of wood or coal ; 

 this is occasioned by carbonic oxide, which is formed 

 in the midst of the mass of burning fuel, where the 

 carbon, being unable to get enough oxygen to form 

 carbonic acid, produces this gas, which, when it 

 reaches the top of the fuel, meets with fresh air, and 

 combines with a further quantity of oxygen. When, 

 however, a charcoal fire is burning slowly, a quantity 

 of carbonic oxide escapes into the air without being 

 burnt into carbonic acid ; and its poisonous nature is 

 often shown, when persons have foolishly placed a 

 pan of burning charcoal in a close bedroom. The 

 charcoal is not only abstracting the oxygen of the 

 air, and converting it into carbonic acid, which can- 

 not support life, but is also forming quantities of the 

 highly poisonous gas, carbonic oxide, the presence of 

 which in a room, in any considerable quantity, is sure 

 to destroy life. 



130. Besides these two compounds of carbon, there 

 is yet a third, intermediate in composition between 

 carbonic oxide and carbonic acid, though very differ- 

 ent from either in its properties ; this substance is 

 oxalic acid, a strong, and very poisonous acid. Oxalic 

 acid occurs in many plants, and may be easily form- 

 ed artificially (503); it is a white solid substance, 

 soluble in water, in which it forms a very sour solu- 

 tion ; and has a strong affinity for bases. It has 

 never been formed direct from carbon and oxygen. 



7 



