112115. CALCIUM, PARARABIN, ETC. 93 



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

 pitate. (Cf. 233.) 



112. Estimation of Pararabin alone. If pararabin 1 alone is 

 present, the estimation may be conducted as described in 111, 

 with the exception, of course, that the determination of calcium is 

 unnecessary. After precipitation with 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.) 



1 1 3. Estimation 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 liquid the 

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

 in another the glucose produced from the starch estimated by 

 titration with Fehling's solution ( 83). 



The modification necessary when starch alone is present needs 

 no special description. 



114. Estimation of Oxalate of Calcium, Starch, and Pararabin. 

 The following is the method I have adopted when oxalate of 

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

 added to the substance under examination in the proportion of 

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

 After cooling to 40 or 50, a centigram or more of good, active 

 diastase 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 alone. If a vegetable substance, 

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

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



1 Compare Reichardt, Ber. d. d. Chem. Ges. viii. 807 (1875) (Journ. Chem. 

 Soc. xxviii. 1179). 



