•94 SUBSTANCES SOLUBLE IN DILUTE ACID. 



ment with various solvents, a method that I published in 18611 

 may be adopted by which the sub^ances that accompany the 

 starch are removed. The powdered material is mixed with 

 30 parts of a 4 per cent, solution of caustic potash in alcohol, and 

 heated to 100° for a day or two in a well-closed flask. After 

 filtering and washing with spirit till free frotti alkali, the substance 

 on the filter is exhausted with water; and to effect this it is 

 advisable to transfer it to a beaker. ■ The residue insoluble in cold 

 ■water is boiled with dilute hydrochloric atoid, and , treated as 

 directed in § 113. The caustic potash acts upon the foreign sub- 

 stances -which interfere with the direct estimation of the starch, 

 rendering them soluble partly in alcohol, partly in water, whilst 

 the starch itself is not attacked. (See § 243.) 



' Joum. f. Landwirthsch (May, 1862), and Pharm. Zeitsohr. f. Kussland, 

 i. 41. For the estimation of starch as glucose after the action of dilute 

 sulphuric acid, see Musoulus, Chem; Centralbl. 1860, p. 602 (Am. Joum. 

 Pharm. xxxii. 433) ; andPhilipp, Zeitsohr. f. anal. Chem. N. F. iii. 400. Sachsse 

 (Zeitschr. f. anal. Chem. xvii.231, 1878; Year-book Pharm. 1878, 97), has shown 

 that the inversion is better effected hj hydrochloric Acid — 1 per cent, of the- 

 weight of the liquid. Both Sachsse and Kageli found that the analyses of 

 starch were more accurately expressed by the formula 6C()HjqOjj + HjO, than 

 by that usually adopted, viz., CgHjoOj. 



