OXALATE AND PHOSPHATE OF LIME. 239 



oxalate of ammonia, and afterwards the phosphoric 

 acid by sulphate of magnesia and ammonia, as in No. 9. 



When the mixture of the two salts is treated with 

 concentrated sulphuric acid, oxalic acid is converted 

 into carbonic acid and carbonic oxide, so that by 

 employing the apparatus described in the article upon 

 alkalimetry, its amount may be inferred from the loss 

 of weight. 



By gently heating the mixture with an excess of 

 finely-powdered binoxide of manganese or neutral 

 chromate of potassa, or with binoxide of lead and di- 

 lute sulphuric acid, all the oxalic acid is converted into 

 carbonic acid, the quantity of which may be determined 

 by the use of the apparatus above alluded to. 2 equivs. 

 of carbonic acid correspond to 1 equiv. of oxalic acid. 



If binoxide of lead be employed in this operation, 

 the quantitative determination of the phosphoric acid 

 may be effected at the same time; for this purpose, 

 the mixture is digested for some time, to liberate the 

 whole of the phosphoric acid; several volumes of 

 alcohol are then added, in order to separate the sul- 

 phate, of lime, the solution filtered, and the residue 

 washed with alcohol. From the filtrate, after the 

 evaporation of the alcohol, the phosphoric acid may 

 be precipitated by sulphate of magnesia and ammonia. 



A very accurate method of estimating oxalic acid 

 consists in converting it into carbonic acid by means 

 of a solution of terchloride of gold, weighing the 

 reduced gold, and calculating thence the amount of 

 oxalic acid ; 3 equivs. of the latter reduce 1 equiv. of 

 gold = 197. 



For this purpose the mixture of the two salts is 

 dissolved in the smallest possible quantity of hydro- 

 chloric acid (a large excess impedes the reduction in 

 gold), mixed with an excess of a solution of terchloride 

 of gold, or better, of sodio-chloride of gold, diluted 

 with much water, and heated to ebullition. The re- 



