§§ 112^115. CALCIUM, PABARABIN, ETC. 93 



estimated by determining the nitrogen in a portion of the preci- 

 pitate. (C£ § 233.) 



§ 112. Estinuitim of PararaUn alone. — If pararabin^ alofle is 

 present, the estimation maybe conducted as described in § 111, 

 trith the exception, of course, that the detertnination of calcium is 

 unnecessary. After precipitation ivith alcohol, pararabin swells 

 in contact with water^ but does not dissolve unless an acid be 

 added. It is precipitated by alkalies, and does not yield arabinose 

 under the influence of dilute sulphuric acid. (Cf. § 245.) 



§ 113. EstimaHon of Starch and Oxalate of Calcium. — If pararabin 

 is absent, but oxalate of calcium and starch are present together, 

 the material under examination may be boiled (not digested on a 

 water-bath) with 1 per cent, hydrochloric acid for four hours in a 

 flask provided with an upright condenser. The flask is weighed 

 before and after boiling, and any water that may have been lost 

 by evaporation replaced. In one portion of the filtered hquid the 

 oxalate of calcium may be determined as directed in § 110, and 

 in another the glucose produced ffom the starch estimated by 

 titration with Fehling's solution (§ 83). 



The modification necessary when starch alone is present needs 

 uo special description. 



§ 114. Estimation of Oxalate of Galciwm, Starch, and Pararahin. — 

 The following is the method I have adopted When oxalate of 

 calcium, starch, and pararabin are present' together. Water is 

 added to the substance nnder examination in the proportion, of 

 10 cc. for every gram, and the whole brought to the boiling-point. 

 After cooling to 40° or 60°, a centigram or more of good, active 

 diasta.se is added, and the maceration continued at the same 

 temperature until the starch-paste is completely liquefied. The 

 residue, after filtering and washing, is treated according to § 111. 

 A measured quantity of the filtrate containing the maltose and 

 dextrin produced from the starch is acidified with hydrochloric 

 acid and boiled as directed in § 113, the glucose being finally 

 estimated with Fehling's solution and calculated into starch. 



§ 115. Estimation of Starch (done. — If a vegetable substance, 

 especially one rich in mucilage, metarabic acid, pararabin, gluco- 

 sides, etc., is to be examined for staj-ch without previous treat- 



' Compare Eeichardt, Ber. d. d. Ohem. Ges. viii. 807 (1875) (Journ. Chem. 

 Soo. xxviii. 1179). 



