26 Prof. Johnston on the Separation of the 



wholly converted into carbonate of lead. At a higher tem- 

 perature the carbonic acid is driven off. 



Water decomposes it, extracting when boiled over the salt 

 the greater part of the nitrate, and leaving nearly pure oxa- 

 late; a small portion of the double salt being dissolved at the 

 same time, which precipitates again on cooling. Thus 24f*26 

 grs. boiled in water left 12'70 grs. of insoluble residue, or 

 52'35 per cent. ; the quantity of oxalate in the salt being only 

 50'016 per cent. When newly precipitated, or before it has 

 been dried at 212°, it is much more readily decomposed, so 

 that it cannot be washed on the filter even with dilute nitric 

 acid without decomposition. 



10*59 grs. heated to nearly 500 Fahr. lost before any trace 

 of red fumes appeared 0*56 = 5*28 per cent, of water. Three 

 successive portions on heating to redness left respectively 

 67*51, 67*55, and a purer variety 67*28 per cent, of oxide of 

 lead. 



These results agree with the formula PIN + PIC + 2 HO. 



Exper. Calcul. 



Or, Oxide of lead 67*28 67*312 



Acids 37*54. 37*263 



Water 5*28 5*425 



100* 100* 



I met with this salt in the course of an examination of the 

 action of nitric acid on certain organic substances. Thus if 

 oil of turpentine or of lemons, the balsams, the sugars, colo- 

 phony, elemi, gamboge and other resins. Burgundy pitch, 

 or indigo be boiled in nitric acid, either dilute or concentrated, 

 and to the acid solution, from which the yellow resin formed 

 during the operation has been precipitated by water, sub- 

 nitrate of lead be added, the new salt falls in great abundance, 

 indicating the production of oxalic acid. Not suspecting the 

 crystals I obtained in this way to be a double salt, I was at 

 much pains in making out their elementary composition by 

 burning with oxide of copper, and I only prepared it directly 

 from a mixture of oxalic and nitric acids after I had completely 

 analysed it. During the action of nitric acid, however, on 

 some, if not upon all the organic substances above mentioned, 

 other acids are formed ; and this is more especially known to 

 be the case in regard to indigo. These acids are held in so- 

 lution along with the oxalic, and continue to be so held after 

 the addition of subacetate of lead to the acid liquid ceases to 

 throw down any more of the double salt. It becomes inter- 

 esting then to examine how far the whole of the oxalic acid 



