§§ 109, 110. EXTBAGTION WITH DILUTE ACID. 91 



YII. 



Examination op Substances Soluble in Dilute Hydro- 

 chloric Acid ; Pararabin, Oxalate of Calcium, etc., and 

 Starch. 



§ 109. Method of EatracUm.— The insoluble residue from § 103 

 is waslied with water (which is best accomplished either by de- 

 cantation or as directed in § 71), and suspended in water con- 

 taining 1 per cent, of hydrochlorie acid, . It is advisable to adhere 

 to the same proportion of menstruum to material as already 

 recommended. The method of procedure now depends mainly 

 Bpbn the presence or absence of starch and of paraxabin (or allied 

 substance). The former may be recognised under the microscope 

 by the blue colour the granules assume when treated with an 

 aqueous solution of iodine.^ 



§110. EsHtnaHon of . Oxalate of Caldum. — The simplest case 

 would be that in which neither starch nor pararabin is present. 

 The only object in digesting with dilute hydrochloric acid would 

 then be to extract oxalate of calcium. To efifect this the digestion 

 should be continued for about twenty-four hours at a temperature 

 of 30°. A measured quantity of the filtrate may be neutralized 

 with ammonia, or mixed with a known quantity of acetate of soda 

 sufficient to convert all the hydrochloric acid into chloride of 

 sodium. The oxalate of calcium, which separates out insoluble 



^ If large quantities of mucilaginous (? albuminous) substances are present, 

 tfais colouration is not perceptible on directly moistening a transverse section 

 with iodine water. The mucilage (or albumen) must be first removed by treat- 

 ment with a dilute (O'l per cent) solution of caustic soda. A stronger 

 solution ihould not be employed, as it might act upon the starch itself. If the 

 residue from § 103 is examined, the treatment with alkali is of course uimeces- 

 sary. For a classification of starches, according to the shape of the granule, 

 see Nageli's ' Monographie der StarkekSrner,' Basel, 1858 ; and Vogl, Zeitschr. 

 d. osterr. Apoth. Ver. 1866, pp. 290, 310. 



