70 SUBSTANCES SOLUBLE IN WJTER. 



should, be estimated in a portion of the filtrate from § 73 or 

 § 7% by precipitation with acetate of copper (cf. § 50), and de- 

 ducted from the totaJ organic acids. 



§ 81. Quditatiw Sepandion. — If the lead precipitate is at first 

 amorphous but becomes crystalline on standing, maZic or /wwarjc 

 flcjrfi may be present (See also §§ 214, 220,, 221.) 



The acids thus precipitated may be further qualitatively examined 

 oy 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 prefcipitate is produced which dilute 

 acetic acid fails to dissolve completely, acalk add is probably 

 present." (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 

 (§ 2I7) dissolves, r.acemate (§ 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 precipita,te in the cold the solution 

 should be boiled. Any turbidity that may now occur would 

 iadic&ie citric acid. (§§215, 216, 218.) 



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

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

 salt in 50 per cent; alcohol. The liquid to 1)6 tested is divided 

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

 added to the other. Any crystals of acid aoonitate 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. Sea also § 216.) 



I think it is very probable that the secalled Marattin is aconi- 

 tate of calcium (§ 102). Spbeero-ctystals of this substance were 



1 For the solubility of malate of lead, In warm dilate acetic aoidi and the 

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

 ChemiBj xiv. 373 (Journ, Chem. Soo. xxix. 375). 



" Oxalate of calcium (§§ 100, 219)oft«n settles slowly and on filtration passes 

 throngh the pores of the filter, Mucl. hag shown (^itschr. f. anal. Ohemie, 

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

 alutniriium salts are pr^eot. 



