458 Gooch and Ward — Copper Oxalate in Analysis. 



about 0*0004 grm. of that taken ; thirdly, that treatment by 

 oxalic acid in 50 per cent alcohol fails to precipitate about 

 0*0020 grm. of copper from amounts less than 0'0200 grm., 

 while for amounts exceeding that limit the copper is nearly 

 all recovered ; and, fourthly, that in volumes of 50 cm3 or 100 cm3 , 

 consisting of 50 per cent acetic acid, the copper oxalate is 

 thrown down completely, the presence of nitric acid to the 

 extent of 10 per cent making the nitration more effective with- 

 out influencing the solubility, while at a volume of 150 cm3 the 

 precipitation is complete provided the acetic acid makes up 

 two-thirds of the volume. 



The best and most convenient procedure for the precipitation 

 of small amounts as well as large amounts of copper oxalate 

 ideal in composition consists, therefore, in adding 2 grm. or 4 

 grm. of oxalic acid to 50 cm3 or 100 cm3 , respectively, of the 50 

 per cent acetic acid solution of the copper salt containing 5 

 per cent to 10 per cent of nitric acid. The permanganate titra- 

 tion of the washed oxalate, in presence of sulphuric acid, gives 

 very accurate determinations of the copper. 



