310 



half an hour, filter, saturate the filtrate with acetic acid in excess, 

 filter again if necessary, and add lime-water or acetate of lime. In 

 the presence of oxalic acid a considerable turbidity is immediately 

 })roduced. To determine the qiiantity of oxalic acid, precipitate- 

 the acid liquid with a sufficient quantity of acetate of lime and 

 convert the precipitate by heat into carbonate of lime. One hun- 

 dred parts carbonate of lime represent 72 parts oxalic acid. 



(/) Add to the liquid, separated by filtering from the lead 

 j»recipitate under e, and to the first portions of water used for 

 washing the same, slowly and under continual stirring, liquor of 

 ammonia, to a very slightly acid condition. (Any excess of am- 

 monia must be again corrected by acetic acid). The precipitate- 

 obtained hereby is of less bulk than the first, but lighter and 

 usually of pale-yellow colour. It contains no sulphuric, phosphoric, 

 or oxalic acids, but may contain either traces of other acids preci- 

 pitable in acid solutions by acetate of lead, or acids precipitable 

 by acetate of lead only from neutral solutions; or acids of both 

 kinds. Its examination may therefore serve either for completing 

 the analysis of that portion of the lead-precipitate which is soluble 

 in acetic acid (e, |3, 1), or for the discovery of new acids. But, 

 before proceeding any further, add a little acetate of lead, until a 

 precipitate is no longer produced. 



Collect the precipitate after subsiding on a filter, wash, spread a 

 part of it on glass or porcelain and let dry; susjiend the other part 

 in absolute alcohol and decompose with sulphuret of hydrogen. 

 After the sulphide of lead has subsided, and when the liquid has- 

 become clear and has lost the smell of sulphuret of hydrogen, it is 

 filtered and the filtrate is cautiously evaporated. Test the remain- 

 ing liquid, freed from alcohol, on such acids as have been found 

 under e, /3, 1, and observe any discrepancies. Should the precipi- 

 tate contain only one acid, the dried portion of it serves for 

 determining its constitution. 



{(j) Mix the liquid, separated from the precipitate, with the first 

 portion of the water used for washing the same, and add subacetate- 

 of lead. The white or yellowish-white precipitate obtained thereby 

 contains no tannic acids, and probably of other acids only a few; 

 no gum or sugar, which, though also precipitable by subacetate of 

 lead, do not pass into the ethereous extract, or only to a very slight 

 extent. 



Let the above precipitate subside, collect in a filter, and wash 

 out. The washing has to be interrupted as soon as decomposition 

 sets in ; which is recognised by the milky appearance of the 

 water passing through the filter. Now, s\isj)end the precipitate 

 in a glass-jar in about ten times its volume of water, decompose 

 with sulphuret of hydrogen, keep the whole at the air until the 

 excess of the gas has disappeared and the liquid has become cleax", 

 filter, concentrate the filtrate, try its physical and chemical pro- 



