92 SUBSTANCES SOLUBLE IN DILUTE ACID. 



in acetic acid, is allowed to settle, and when the supernatant liquid 

 is perfectly clear it is poured off, and the precipitate transferred 

 to a fine filter, washed and dried. It may then be converted 

 either into carbonate by gentle, or into oxide by strong ignition, 

 and from the weight of either the amount of oxalate calculated. 

 The filtrate and Avashings are evaporated to dryness, and the 

 residue weighed. As the amount of chloride of sodium and un- 

 decomposed acetate is known, it will thus be ascertained if other 

 substances (albuminoids, § 223 et seq.) have been dissolved by 

 dilute hydrochloric acid. 



Instead of estimating the oxalate as carbonate or oxide, the 

 washed precipitate may be dissolved in dilute sulphuric acid, and 

 the oxalic acid determined by titration with permanganate of 

 potassium. (Cf. §§ 81, 219.) 



Microscopical Examination. — Oxalate of calcium is always de- 

 jiosited in plants in the crysfalline condition, and its presence 

 may therefore be confirmed by microscopic examination. The 

 crystals must be insoluble in water, alcohol, and ether, but soluble 

 in dilute hydrochloric acid. 



It should also be ascertained, by means of the microscope, if all 

 the oxalate has been dissolved by the treatment directed in § 109. 

 If that is not the case, the maceration with dilute acid should be 

 relocated. 



§ 111. Estimation of Oxalate of Calcium and Pararalin. — If the 

 oxalate of calcium is accompanied by pararabin, but not by starch, 

 the maceration is continued for twenty-four hours as before ; but 

 previous to filtering, the whole is rapidly raised to the boiling- 

 l^oint in a flask provided with an upright condenser. A measured 

 quantity of the filtrate (filtered whilst hot) is neutralized with 

 ammonia, and mixed with 2 to 3 volumes of 90 per cent, alcohol. 

 The precii^itate, which contains oxalate of calcium and pararabin, 

 is collected on a tared filter, washed with 60 to 70 per cent, 

 alcohol, dried, and weighed. It is then incinerated, the ash cal- 

 culated to oxalate of calcium, and deducted from the weight of 

 the precipitate. The remainder is the weight of the pararabin. 



The filtrate and washings from the precipitate may be evapo- 

 rated to dryness as directed in § 110, in order to ascertain if other 

 substances have been dissolved. Here, too, all)uminous substances 

 may jjossibly ho found, and they may also l)e present in the 

 precipitated j^ararabin. )Should that be the case, tliey may be 



