70' . SUBSTANCES SOLUBLE IN WATER. 



should be estimated in a portion of the nitrate from 73 or 

 76, by precipitation with acetate of copper (cf. 50), and de- 

 ducted from the total organic acids. 



81. Qualitative Separation. If the lead precipitate is at first 

 amorphous, but becomes crystalline on standing, malic or fumaric 

 acid 1 may be present. (See also 214, 220, 221.) 



The acids thus precipitated may be further qualitatively examined 

 by suspending the moist precipitate obtained as directed in 80 

 in pure water and decomposing with sulphuretted hydrogen. The 

 filtrate from the sulphide of lead is evaporated on the water-bath 

 to a small bulk and, when the odour of sulphuretted hydrogen 

 has disappeared, lime-water is added to the cooled liquid till the 

 reaction is alkaline. If a precipitate is produced which dilute 

 acetic acid fails to dissolve completely, oxalic acid is probably 

 present. 2 (See also 214, 218, 219.) If, on the other hand, 

 it is entirely soluble in acetic acid, a fresh portion should be 

 tried with solution of chloride of ammonium. Tartrate of calcium 

 (217) dissolves, racemate (218) does not. In the latter case care 

 should be taken not to mistake phosphate for racemate of calcium. 



If lime-water has caused no precipitate in the cold the solution 

 should be boiled. Any turbidity that may now occur would 

 indicate citric acid. ( 215, 216, 218.) 



Aconitic acid is not thrown down by lime-water even on boiling, 

 but it is characterized by the slight solubility of its acid ammonium 

 salt in 50 per cent, alcohol. The liquid to be tested is divided 

 into two portions, one of which is neutralized with ammonia and 

 added to the other. Any crystals of acid aconitate of ammonium 

 which separate out should be washed with 50 per cent, alcohol. 

 From this salt the acid may be isolated by adding a slight excess 

 of sulphuric acid and shaking with ether. Its identity may be 

 established by the ultimate analysis of the calcium, silver and 

 ammonium salts. (See also 216.) 



I think it is very probable that the so-called Marattin is aconi- 

 tate of calcium ( 102). Sphaero-crystals of this substance were 



1 For the solubility of malate of lead in warm dilute acetic acid, and the 

 deposition of a crystalline salt on cooling, see Hartsen, Zeitschr. f. anal. 

 Chemie, xiv. 373 (Journ. Chem. Soc. xxix. 375). 



2 Oxalate of calcium ( 100, 219)often settles slowly and on nitration passes 

 through the pores of the filter. Muck has shown (Zeitschr. f. anal. Chemie, 

 ix. 451) that the precipitate is much easier to manipulate if small quantities of 

 aluminium salts are present. 



