HEAVY METALS. 



39 



raspberry seeds, indicating that raspberry pulp had been used as the 

 basis of the jam. It is said that in Europe the fig serves as the basis 

 of a large number of jams, but its use can easily be detected by examina- 

 tion of the seeds. It is probably true that the exhausted pulp left from 

 the manufacture of jellies is sometimes used as a basis for the poorer 

 grade of jams. 



HEAVY METALS. 



Tin is almost universally present in goods put up in tin cans, owing 

 to the ease with which the metallic surfaces are attacked. Canned 

 fruits as a rule dissolve a larger amount of tin than other classes of 

 foods, not alone because of their high acidity, but because the sirup 

 in which the fruits are put up allows better contact with the walls of 

 the can and better diffusion of the acids than is possible in many other 

 classes of foods, such as meats, fish, etc. 



The frequent occurrence of zinc in canned foods makes the deter- 

 mination of this metal of particular importance. The zinc present in 

 the product is undoubtedly due in most cases to the zinc chlorid used 

 as a flux in soldering. Since this salt ma}^ readily be removed by 

 washing after the cans are made, care should be taken b}^ the manu- 

 facturer that necessar}^ precautions are used to remove this objection- 

 able material. This point is well illustrated by the work of Hilgard 

 and Colby, "" in which the presence of an excessive amount of zinc 

 chlorid in canned asparagus was traced to the use of soldering fluid. 

 By employing care in the manufacture of the cans and by careful wash- 

 ing before using, the manufacturers were able to reduce the amount of 

 zinc to an inappreciable quantity. 



The following table gives the results of the determination of heavy 

 metals in 25 samples of fruit products: 



Table 8. — Percentage of heai^y metal? in fruit products. 



Serial 

 num- 

 ber. 



Kind of fruit. 



20232 Apple jelly 



19900 Apricots 



20027 Cherries 



20248 I Cherries 



19895 Cherries 



19898 \ Cherries (black) 



19881 j Currants 



19958 ! Currant and raspberry 



19891 ' Cranberries 



20231 ! Grapes 



20233 Peaches 



19893 Peaches 



20134 Pears 



Acidity Metals, milligrams 

 of fruit as per kilogram. 



I per cent — — - 



H2S04. I Tin. Zinc. 



0.592 



.823 

 .702 

 .401 

 .457 

 .477 

 .455 

 .303 



.485 

 .205 



None. 

 264 

 269 

 168 

 458 

 216 

 224 

 122 

 429 

 400 

 96 

 176 

 133 



None. 



None. 



None. 



Trace. 



Trace. 



None. 



None. 



None. 

 28 

 16 

 45 

 11 

 104 



" California Experiment Station Report, 1897-98, p. 159. 



