24 

 hefelmann's method of detecting zinc in evaported apples. 



Hefelmaun uses the following method for detecting zinc in evaporated 

 fruits (Cbemiker-Zeitung, vol. 18, j). 44) : 



Two hundred grams of the evaporated fruit are placed in a wide-neck flask and 

 covered with enough 25 per cent hydrochloric acid to fully irumerse all and allowed 

 to stand, with frequent shaking, for three hours, at a temi^erature of from 40° to 60°. 

 From two to three times as much water is added as the volume of the hydrochloric 

 acid employed, and the iiask is then placed aside, with frequent shaking, in a warm 

 place for twenty-four hours. The contents of the flask are then filtered with the 

 help of a suction pump, washed with 1 per cent hydrochloric acid and finally with 

 boiling water. The extract is concentrated to about one-third of its volume and 

 oxidized for half a day with small quantities of potassium chlorate. The free chlorin 

 is driven off and the mass again filtered, the filtrate supersaturated with ammonia 

 and treated with ammonium sulphide. After twelve hours the precipitate is separated 

 by filtration and oxidized with aqua regia, heated until the chlorin odor has disap- 

 peared, strongly supersaturated with ammonia, acetic acid added, and the zinc sul- 

 phide precipitated with hydrogen sulphide. After the precipitation is complete, 10 

 grams of ammonium nitrate are added for each 100 cubic centimeters of the liquid in 

 order to secure a better separation of the zinc sulphide, which, after standing for 

 twenty-four hours, is separated by filtration and washed with water containing 

 hydrogen sulphide and ammonium nitrate. It is then ignited and weighed as zinc 

 oxid, the precipitate being washed with concentrated ammonium nitrate solution 

 before ignition. 



Hefelmann expresses the erroneous opinion that the white or yellow- 

 white color and moist condition of American evaporated apples is due 

 to their treatment with a zinc salt for bleaching purposes. 



NIEDERSTADT'S METHOD OF DETERMINING ZINC. 



At a meeting of the pharmaceutical section of the German Associa- 

 tion for the Advancement of Science, at Liibeck, in September, 1895, 

 Dr. Niederstadt, of Hamburg, read a paper on zinciferous apples. 

 (Chemiker-Zeitung, vol. 19, p. 1757.) 



Niederstadt uses the following method for the quantitive determina- 

 tion of zinc in evaporated fruits : 



Forty grams of the finely cut apples are ignited in a platinum dish until the car- 

 bonized mass can be easily powdered in a mortar. This carbonized material is then 

 extracted with hydrochloric acid, the extract separated by filtration and oxidized 

 with potassium chlorate. Afterwards liydrogeu sulphide is introduced to test for 

 lead and copper, which if found are separated by filtration. The filtrate is again 

 oxidized with potassium chlorate and the zinc andiron j)recipitated with ammonium 

 sulphide, the precipitate separated by filtration, dissolved in hydrochloric acid, again 

 oxidized with potassium chlorate, neutralized with sodium carbonate, acidified with 

 acetic and the iron precipitated with sodium acetate and separated by filtration. In 

 the filtrate the zinc is precipitated with hydrogen sulphide, separated by filtration, the 

 zinc sulphide dissolved in hydrochloric acid, precipitated by sodium carbonate, and 

 ignited. In this way 3 milligrams of zinc oxid which were added to apples free of 

 zinc were recovered without loss. 



