30 



FRUITS AND FRUIT PRODUCTS. 



The pectin precipitate had the following content of nitrogenous 

 material: 



DETECTION OF STARCH. 



In the detection of starch it is first necessary to destroy the color 

 of the fruit or fruit product. This is accomplished by bringing the 

 solution of jelly or jam nearly to the boiling point, and after the addi- 

 tion of several cubic centimeters of dilute (1 to 3) sulphuric acid, adding 

 potassium permanganate with constant stirring until the color disap- 

 pears. By this treatment the starch remains unaffected, and the solu- 

 tion may be tested with iodin. If starch is found to be present it is 

 well to examine the product microscopically in the case of jams and 

 marmalades. If the starch is normally present in the fruit this point 

 is easily decided by such an examination, as the starch grains may be 

 readily detected within the cell walls after the treatment with iodin. 



DETERMINATION OF HEAVY METALS. 



Treat 100 grams of the preserve directly in a large porcelain evap- 

 orating dish with sufficient concentrated sulphuric acid to thoroughly 

 carbonize the mass. If much water is present evaporate the material 

 to a sirupy consistency before treating with the acid. From 10 to 15 cc 

 of strong acid has been found sufficient to thoroughly carbonize the 

 amount specified. Gently heat over a Bunsen burner until all danger 

 of foaming is past, which will require not more than three minutes; 

 then transfer the dish to a muffle furnace and keep it at a low red heat 

 until all organic matter is destroyed. It is occasionally found neces- 

 sary to add a few drops of nitric acid to completely destroy organic 

 matter. When the material is completely ashed allow the dish to 

 cool; add 25 cc of hydrochloric acid (1 to 8) and evaporate on a water 

 bath to dry ness; take up with water and acidify with two or three 

 drops of hydrochloric acid. Transfer to a beaker without filtering 

 and treat with hydrogen sulphid. After heating upon a water bath 

 for a few minutes the precipitate and the insoluble residue are col- 

 lected upon a filter. The precipitate and residue may contain sulphid 

 of tin, lead, and copper, and oxid of tin; the filtrate will contain any 

 zinc that is present. Fuse the sulphid precipitate and insoluble ash 

 residue with about 3 grams of sodium hydroxid in a silver crucible for 

 a half hour to render soluble any insoluble tin compounds. Dissolve 

 the mass with hot water and slightly acidify with hydrochloric acid. 



