592 POODS AND FOOD ADULTERANTS. 



by gently boiling the acid liquid for four hours, after which the flask and 

 contents are cooled, neutralized by the addition of sodium hydrate, made 

 up to a definite volume and the copperoxide reducing power determined. 

 The latter operation is best carried out by the method used in this labo- 

 ratory, in which asbestos-tipped filtering tubes are used for the end reac- 

 tion. 1 The reducing power being calculated as dextrose 5 10 parts equal 

 9 parts of anhydrous starch. 



Professor Weber used a rough method for the direct estimation of 

 starch in his samples, which he describes as follows: 2 



One grain was weighed off, transferred to a small beaker, covered with water, al- 

 lowed to stand until action had ceased, filtered and washed, residue spurted by means 

 of a wash-bottle into a flat-bottomed platinum dish, allowed to settle, the superna- 

 tant water removed as far as possible by means of a pipette, the remainder of water 

 evaporated, the residue dried at 100 C. and weighed. The residue was then incin- 

 erated and the amount of ash deducted from abo%^e weight. In case of alum powders 

 the ash remaining after ignition was A] Z O 3 , which was contained in the residue dried 

 at 100 C. as A1 2 (OH) 6 ; consequently the A1 2 O 3 was calculated as A1 2 (OH) 6 before de- 

 ducting. 



This method was carried out upon the entire series of samples exam- 

 ined here. In many cases it gave results agreeing quite closely with 

 those obtained by the direct estimation, but in some samples the re- 

 sults were entirely too high. It is not applicable to alum powders even 

 with the correction made above. For a rough method it answers fairly 

 well and it is quite easy of execution. 



ESTIMATION OF PHOSPHORIC ACID. 



This determination was made in the same manner as in fertilizers, as 

 prescribed by the Association of Official Agricultural Chemists at their 

 last meeting, as follows: 3 



Weigh out 2 grams of the sample, ignite carefully in a muffle, and 

 treat with 30 cubic centimeters concentrated nitric acid. 



Boil gently until all phosphates are dissolved and all organic matter, 

 destroyed; dilute to 200 cubic centimeters; mix and pass through a 

 dry filter; take 50 cubic centimeters of filtrate; neutralize with am- 

 monia. To the hot solutions for every decigram of P 2 O 5 that is present 

 add 50 cubic centimeters of molybdic solution. Digest at about 65 0. 

 for one hour, filter, and wash with water or ammonium nitrate solution. 

 (Test the filtrate by renewed digestion and addition of more molybdic 

 solution.) Dissolve the precipitate on the filter with ammonia and hot 

 water and wash into a beaker to a bulk of not more than 100 cubic centi- 

 meters. Nearly neutralize with hydrochloric acid, cool, and add mag- 

 nesia mixture from a burette; add slowly (one drop per second), stir- 

 ring vigorously. After fifteen minutes add 30 cubic centimeters of 

 ammonia solution of density 0.95. Let stand several hours (two hours 



'Fully described in Bull. No. 15, p. :. 

 2 Communicated to the author in MSS. 

 3 Bull, No. 19, Chem. Div. U. S. Dcp't Ag'l, p. 58. 



