On Oxalic Jcid. 245 



are five in lumiber ; namely, water, carlonic acid, carbonic 

 oxide, carbureted hydrogen, and charcoal. 



2. The water is never quite pure. Though no sensible 

 portion of oil can be perceived in it, yet it lias always the 

 peculiar smell of the water obtained during the distillation 

 of wood ; a smell which is usually ascribed to oil. It com- 

 monly shows traces of the presence of ammonia, changing 

 vegetable blues to green, and smoking when brought near 

 muriatic acid ; but this minute portion of ammonia is pro- 

 bably only accidentally present. All the oxalates which I 

 decomposed by distillation, were obtained by double de- 

 composition from oxalate of ammonia; and though they 

 were washed with sufficient care, yet I think it not unlikely 

 that a minute portion of oxalate of ammonia might con- 

 tinue to adhere. Practical chemists know the extreme diffi- 

 culty of removing every trace of a salt with which another 

 has been mixed. 



The carbonic acid remains partly combined with the base, 

 which always becomes a carbonate, and partly makes its 

 escape in the form of gas. 



The carbonic oxide and carbureted hydrogen make their 

 escape in the form of gas : the charcoal remains in the re- 

 tort mixed with the base, to which it communicates a gray 

 colour: the quantity of it depends in some measure upon the 

 heat. If the oxalate was ex|)Osed to a very violent heat, no 

 charcoal at all remains. Hence it probably acts upon the 

 carbonic acid united to the base, converting it into carbonic 

 oxide, as happens when a mixture of a carbonate and char- 

 coal is heated. 



3. I was induced to examine this decomposition with 

 considerable attention, because I conceived that it would 

 furnish the means of estimating the composition of oxalic 

 acid; and I pitched upon oxalate of lime, as the salt best 

 adapted for the purpose I had in view. A determinate 

 quantity of this salt was put into a small retort, and gradu- 

 ally heated to redness. This retort was connected with a 

 pneumatic trough by means of a long glass tube, having a 

 valve at its extremity which allowed gas to issue out, but 



Q 3 prevented 



