109, 110. EXTRACTION WITH DILUTE ACID. 91 



VII. 



EXAMINATION OF SUBSTANCES SOLUBLE IN DILUTE HYDRO- 

 CHLORIC ACID j PARARABIN, OXALATE OF CALCIUM, ETC., AND 

 STARCH. 



109. Method of Extraction. The insoluble residue from 103 

 is washed 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 hydrochloric acid. It is advisable to adhere 

 to the same proportion of menstruum to material as already 

 recommended. The method of procedure now depends mainly 

 upon the presence or absence of starch and of pararabin (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. 1 



110. Estimation of Oxalate of Calcium. 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 effect 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 



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

 this 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 should 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 unneces- 

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

 see Nageli's ' Monographic der Starkekorner,' Basel, 1858 ; and Vogl, Zeitschr. 

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



