1406 



FOODS AND FOOD ADULTERANTS. 



More exact comparisons can be made looking sidewise through the 

 tubes at a window covered with white paper and shaded from direct 

 sunlight. 



The following table prepared by Mr. Given enables one to deter- 

 mine at a glance the percentage of potassium nitrate in a given sample 

 from the number of cubic centimeters of standard solution employed, 

 if the above directions are followed in detail: 



TABLE 9. Per cent potassium nitrate. 



DETECTION OF BORAX OR BORIC ACID. a 



Fifty grams of the meat are moistened with water, a sufficient quan- 

 tity of milk of lime added to ensure an alkaline reaction, and the whole 

 is evaporated to dry ness and ignited. It is not necessary that the car- 

 bon should be entirely oxidized, but the ignition should be at so high 

 a temperature that a colorless extract may be obtained from the ash 

 with water. The ignited product is extracted with water, to which 

 sufficient acetic acid to decompose carbonates has been added, and fil- 

 tered. The insoluble portion contains all fluorids and silico-fluorids 

 present, and may be tested as directed hereafter. Neutralize the fil- 

 trates with hydrochloric acid and add about 1 cc of concentrated 

 hydrochloric acid for each 15 cc of liquid. A strip of turmeric paper 

 dipped into the solution and dried on the water bath is changed in the 

 presence of boric acid to a deep cherry red, which is converted first 

 into dark purple, then green, and finally greenish black on being 

 made alkaline with ammonium or sodium hydroxid. If the hydro- 

 chloric acid is not present in sufficient quantity, the reaction loses in 

 delicacy, while if present in too great a quantity the turmeric paper 

 takes on a dirty brown color which masks the reaction given by a 

 small amount of boric acid. In the latter case, however, the addition 

 of alkali will produce the change of colors mentioned above when 

 boric acid is present. 



"The determinations of preservatives for this bulletin were made by Mr. Munson. 



