110 79. BASES a:n"d acids with reagents. 



of the substance to be examined containing about 2.5 

 grms. of starch with water, heat to 70° C, add one of the 

 portions of the extract of malt, put the other portion into 

 another flask, and digest both precisely alike 3 or 4 hours 

 on the water-bath, at a temperature of about 60° or 70° 

 C. Then bring both liquids to about 200 c.c. by addition 

 of water, add 20 c.c. of a solution of basic plumbic ace- 

 tate (§ 24, a) to each, shake vigorously, add water again 

 until the volume of each liquid is exactly 500 c.c, at a 

 temperature of nearly 15°, let the mixture stand until the 

 solid matters settle, and then determine the glucose in an 

 aliquot part of each liquid with the aid of the standard 

 Fehling's solution (§ 81). 10 c.c. of that solution corres- 

 pond to 0.045 grm. of starch. The two liquids will con- 

 tain equal quantities of glucose, produced from the malt ; 

 therefore, the difference between the amounts of glucose 

 found in the two, or the corresponding difference between 

 the amounts of starch, will be the amount of starch in 

 the substance analyzed. 



2. a. ^1/ sulphuric acid. — ^Dry the substance thoroughly, 

 and digest a quantity of it, supposed to contain about 2.5 

 grms. of starch, 2 hours on the water-bath, with 50 times 

 its weight of a dilute sulphuric acid, containing 1"!^ by 

 volume of concentrated acid, then filter, and wash the 

 residue on the filter carefully. This residue is composed 

 mostly of cellulose. Dilute the filtrate and washings to 

 200 c.c, add about 16 c.c. of concentrated sulphuric acid, 

 and digest again 7 or 8 hours on the water-batli, at 95°, 

 or until a drop of the solution gives no blue color witli a 

 solution of iodine. If the solution is highly colored, add 

 20 c.c. of plumbic acetate, shake vigorously, make the 

 volume of the liquid up to 500 c.c, let the mixture stand 

 if it is necessary to clarify the solution, and determine the 

 glucose in the clenr supernatant liquid with the standard 

 Fehling's solution, 10 c.c. of which correspond to 0.045 

 grm. of starch (§ 81). 



