170 FOODS AND FOOD ADULTERANTS. 



as long as the pan, 5 inches wide and 4 inches high. In this are cut six holes If 

 inches in diameter. At the back of the pan is a stout wire running lengthwise of 

 the stand, 8 inches high, with a bend or depression opposite each hole in the shelf. 

 The digestion flask rests with its lower part over a hole in the shelf and its neck in 

 one of the depressions in the wire frame, which holds it securely in position. Heat 

 is supplied by low Bunsen burners below the shelf. Dr. Jenkins has used asbestus 

 paper under the flasks, but finds that with a little care the naked flame can be applied 

 directly to the flask without danger. 



THE DETERMINATION. 



One gram of the substance to be analyzed is brought into a digestion flask with ap- 

 proximately 0.7 gram of mercuric oxide and 20 cubic centimeters of sulphuric acid. 

 The flask is placed on the frame above described in an inclined position and heated be- 

 low the boiling point of the acid for from five to fifteen minutes, or until frothing has 

 ceased. The heat is then raised till the acid boils briskly. No further attention is 

 required till the contents of the flask has become a clear liquid, which is colorless or 

 at least has only a very pale straw color. The flask is then removed from the frame, 

 held upright, and while still hot, potassium permanganate is dropped in carefully 

 and in small quantity at a time till after shaking the liquid remains of a green or 

 purple color. After cooling, the contents of the flask are transferred to the distilling 

 flask with water, aud to this 25 cubic centimeters of potassium sulphide solution are 

 added, 50 cubic centimeters of the soda solution, or sufficient to make the reaction 

 strongly alkaline, and a few pieces of granulated zinc. The flask is at once con- 

 nected with the condenser and the contents of the flask are distilled till all ammonia 

 has passed over into the standard acid contained in the precipitating flask previously 

 described and the concentrated solution can no longer be safely boiled. This opera- 

 tion usually requires from twenty to forty minutes. The distillate is then titrated 

 with standard ammonia. 



The use of mercuric oxide in this operation greatly shortens the time necessary for 

 digestion, which is rarely over an hour and a half in the case of substances most diffi- 

 cult to oxidize and is more commonly less than an hour. In most cases the use of 

 potassium permanganate is quite unnecessary, but it is believed that in exceptional 

 cases it is required for complete oxidation, and in view of the uncertainty it is always 

 used. Potassium sulphide removes all mercury from solution and so prevents the 

 formation of mercuro-ammonium compounds which are not completely decomposed 

 by soda solution. The addition of zinc gives rise to an evolution of hydrogen and 

 prevents violent bumping. Previous to use the reagents should be tested by a blank 

 experiment with sugar, which will partially reduce any nitrates that are present 

 which might otherwise escape notice. 



This method cannot be used for the determination of nitrogen in substances which 

 contain nitrates or certain albuminoids. 



In case non-album inoid nitrogen is to be determined reference can 

 be made to Stutzer and Ladd.* 



These methods of analysis are suitable to all the spices and have 

 been used with them. They are nothing but general processes, and 

 are dependent for their value on uniformity in the way they are carried 

 out and the manner in which peculiarities of proximate composition in 

 different spices are considered in drawing conclusions. Determinations 

 of particular substances, such as piperine, require, however, modifica- 

 tions, which must be described when discussing the analyses of each 

 spice. 



*Rept. anal. Chem., 5, 162, 163; Abs. Ber., 19, 1885; and Ladd Kept, of New 

 York Agric. Exp. Sta., 1886. 



