Decomposition of Pi/romcconic Acid. 165 



It loses nothing at 212°, even after being kept for three or foiir 

 hours at that temperature. 



The following is the result of analysis, the lead being deter- 

 mined as sulphate by ignition of the salt with a few drops of 

 strong sulphiu'ic acid. 



5 '48 grains substance gave 5 "65 carbonic acid and 0'815 

 water. 5*29 grains substance gave 3" 74 sulphate of lead. 



Calculation. 



Exj)eiiment. , ' — — > 



Carbon . . . 28-12 27-94 Ci" 60 



Hydrogen . . 1-65 1-39 H^ 3 



Oxygen . . . 18-21 18-77 0^ 40 



Oxide of lead . 53-02 51-90 TbO 111-56 



Ibo^O^ 100-00 214^6 



The formula is therefore represented by PbO, C'^IPO^ 



Pijromeconate of Copper. — The ammonio-sulphatc of copper 

 mixed with a warm aqueous solution of pyromeconic acid causes 

 an immediate precipitate of this salt in bright green crystalline 

 needles, which are extremely brittle and easily pulverized. This 

 salt has also been examined by Stenhouse*, who prepared it by 

 boiling the acid with hydrated oxide of copper, and allowing the 

 filtered solution to cool. The crystals require a considerable 

 amount of hot water for their solution, and are very slightly 

 soluble in cold water or alcohol. 



The copper was determined as oxide by heating the salt to 

 redness, and then igniting the residue with nitric acid. It loses 

 nothing at 212°. 



6-00 grains substance gave 1-66 oxide of copper, which calcu- 

 lated per-centage gives 27-66 of oxide of copper, the number 

 27-79 being that corresponding with the formula 

 CuO,CioH-^05. 



Pyromeconate of Iron. — Dr. Stenhouse has observed in the 

 paper before mentioned, that when pyromeconic acid is boiled 

 with hydrated peroxide of iron, and also with the persulphate, 

 it combines with the oxide and forms a brownish-red powder, 

 whicli when neutral is very little soluble in cold water. It may 

 also be obtained, and perhaps more conveniently, by adding 

 pcrchloride of iron to a hot concentrated solution of the acid in 

 water, when the cinnabar-red crystals begin to make their ap- 

 pearance, adhering firmly to the sides and bottom of the vessel. 



Its proj)ertics have been so fully described by Stenhouse, that 

 further remark is unnecessary. 



The crystals were well washed with cold water, until the fluid 



* Mem. anil Proc. Cbcm. Soc. vol. ii. [Phil. Mag. S. 3. vol. xxiv. p, 128.] 



