MESOXALIC ACID 5 



This salt of lead may be decomposed by adding the quantity of 

 sulphuric acid just requisite to saturate the oxide of lead. Or we 

 may separate the lead by passing a current of sulphuretted hy- 

 drogen gas through water with which the mesoxalate of lead has 

 been mixed. If we filter to get rid of the lead, and apply heat 

 to drive off what sulphuretted hydrogen may exist in the liquid, 

 we obtain a solution of mesoxalic acid in water. 



Mesoxalic acid crystallizes readily, though the shape of the 

 crystals has not been determined. Its reaction is strongly acid, 

 and it is very soluble in water. With the salts of lime and ba- 

 rytes it gives precipitates, but only after the addition of ammo- 

 nia. It does not give oxalic acid when evaporated or boiled in 

 an open vessel. Its distinguishing characteristic is to form with 

 the salts of silver, after the addition of a little ammonia, a yellow 

 precipitate, which, on exposure to a gentle heat, is reduced to the 

 metallic state, while a great deal of carbonic acid gas is given off. 

 When mesoxalate of lead is heated with a little nitric acid, it 

 is converted into oxalate of lead, while, at the same time, nitrous 

 gas is given out, showing that oxygen has been added to the acid 

 of the salt. 



When alloxanate of silver is dissolved in boiling water, it does 

 not change colour, but if we add a little ammonia, it becomes 

 yellow, and if the boiling be prolonged, it becomes all at once 

 black, while a lively effervescence takes place. The alloxanate 

 of silver in this case is decomposed into mesoxalate, to which that 

 kind of reaction is peculiar. 



Liebig analyzed the mesoxalate of lead, and obtained 



Carbon, . 6-85 



Hydrogen, . 0-20 



Oxygen, . 12-21 



Oxide of lead, . 80-74 



100-00 



The quantity of hydrogen is so small, that he was of opinion 

 that the acid in reality contains none. In that case it is a com- 

 pound of carbon and oxygen only, like oxalic acid. If the oxide 

 of lead in the salt amount to two atoms, then the atomic weight 

 of the mesoxalic acid will be 6-67. For 80-74 : 19-26 : 1 28 : 6-67. 

 Now the numbers that accord best with the analysis and with 

 this atomic weight are the following : 



