70 SUBSTANCES SOLUBLE IN WATER. 



shoiüd be estimated in a portion of the filtrate 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 j^recipitate is at first 

 amorphous, but becomes crystalline on standing, malic or fumario 

 ackl'^ may be present. (See also §§ 214, 220, 221.) 



The acids thusprecii^itated may be further qualitatively examined 

 by suspending the moist jorecipitate obtained as directed in § 80 

 in pure Avater and decomposing Avith sulphuretted hydrogen. The 

 filtrate from the suli^hide 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 Avith 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 1)oilcd. Any turbidity that may now occur would 

 indicate citric acid. (§§215, 21G, 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 

 Avhich 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 Jllarattin is aconi- 

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



^ 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. Ij73 (Journ. Chein. Soc. xxix. 375). 



- Oxalate of calcium (§§ 100, 21!t)often settles slowly and on filtration passes 

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

 ix. 4.51) that the precipitate is :nuch easier to manipulate if small quantities of 

 aluminium salts are present. 



