BULLETIN No. 90a 
9 
acid is separated without any loss. The substance is now transferred 
to a 500 c. c. Erlenmeyer flask, which is filled to three-fourths of its 
capacity with distilled water. To this solution add at least 2 grams 
of oxalate of ammonia to each gram of pectic acid, and heat in a 
water-bath at 35° C. for three to four hours. Oxalate of ammonia, 
like other salts of organic acids, has the property of dissolving pectic 
acid. Furthermore, this solution is much easier to filter than an 
alkaline p>ectic acid solution. After filtering and washing, precipi¬ 
tate the filtrate with acetate of lime in excess. The precipi.ate con¬ 
sists of oxalate and pectate of lime, from which the pectic acid can 
be separated by washing slowly with alcohol strongly acidified with 
hydrochloric acid. This operation may be avoided if one has 
weighed the amount of oxalate of ammonia used. In this case 
filter the oxalate and pectate of lime on tared filters; wash with 
water, then with alcohol; dry at 100° C. and weigh. Now calcine the 
precipitate obtained, deduct the amount of lime which was com¬ 
bined with the oxalate of ammonia employed, and the residue is 
the lime combined with the pectic acid. The oxalate and pectate of 
lime, minus the oxalate of lime, gives the pectate of lime, and this, 
minus the lime combined with it, gives the pectic acid. 
Glucose .—Five to ten grams of the substance are placed in a 
beaker, with a small amount of water, and allowed to stand for 1 or 
2 hours. Filter, and wash until all the glucose is removed. This 
is generally accomplished when the filtrate and washings amount 
to 200 c. c. Treat this solution with a slight excess of basic acetate of 
lead; filter, and wash thoroughly. Remove the excess of lead with 
sodium carbonate, and determine the glucose in an aliquot part of 
this solution with Fehling’s solution. 
Starch .—The residue from the preceding determination is placed 
in a flask of 250 c. c. capacity, 150 c. c. of distilled water, 4 to 5 c. c. of con¬ 
centrated hydrochloric acid added, and the flask closed by a cork 
having a small glass tube, about three feet long, inserted in it to act 
as a condenser. The flask is then put in a water-bath, and kept at 
the temperature of boiling water for twelve hours, fifiie flask is 
allowed to stand over night; the solution is then filtered off, the 
filtrate neutralized with sodium orbonate, and the washing con¬ 
tinued until all the glucose is washed out, which is generally accom¬ 
plished when the filtrate and washings amount to 200 c. c. The glu- 
close is then determined by Fehling’s solution, as in the preceding- 
case, and the starch calculated from the result. 
Acetic Acid .—The solubility of acetic acid salts in water and alco¬ 
hol precludes the use of the precipitation method of estimating this 
acid. But acetic acid is volatile, and this peculiarity may be advan¬ 
tageously employed to furnish a very simple method for separating 
it. Use a stream of steam to volatilize the acetic acid, which has 
been previously freed from its bases by a stronger non-volatile acid. 
A convenient apparatus for this determination consists of a glass 
