1042 FOODS AND FOOD ADULTERANTS. 



done, hinders this solution of the tin in great measure, but generally there 

 is sufficient metal left bare to allow appreciable quantities to dissolve. 

 The quantity which is taken up from a bare can is of course almost 

 entirely dependent upon the nature of the contents. Highly acid liquids 

 like those which surround some canned fruits dissolve the greatest quan- 

 tity. Goods which have been sulphured also act heavily upon tin, form- 

 ing tin sulphid, which probably then slowly dissolves to some extent. 

 This appearance may be often noticed on the inside of cans which contain 

 corn. The tin sulphid forms soft pasty deposits on the metal, looking 

 very much like mold to the naked eye. Indeed, these spots are very 

 often taken for fungoid growths. The tin sulphid in this form is readily 

 rubbed off into the food by any shaking of the can. 



The formation of the sulphid occurs by virtue of the fact that metals 

 very readily reduce sulphur dioxid, forming a metallic sulphid or 

 hydrogen sulphid, according to circumstances. 



Tin poisoning resulting from the use of canned foods is not often 

 recorded, although it is probable that minor disturbances to health fre- 

 quently occur from this cause. 



In 1880 O. Hehner examined a large number of canned foods, repre- 

 senting most of those thus preserved, for dissolved tin. In most of 

 these it was found. Experiments made on Guinea pigs with doses of 

 stannous hydrate showed a marked poisonous and in many cases a 

 fatal action. This is the state in which tin occurs in foods. Stannic 

 hydrate was found to be relatively harmless. The doses of tin which 

 he employed, though not large in themselves, were, considering the size 

 of a Guinea pig, rather heavy. Still, his conclusion that tin has well- 

 marked toxic properties seems well justified. An abstract of this work 

 is given on page 1164. 



In 1883 Ungar and Bodlander examined a number of samples of 

 canned goods, mainly asparagus. There had been a number of cases 

 of illness resulting from the use of canned asparagus, which led them 

 to make the investigation. Most of the foods examined contained the 

 metal in greater or less quantity. In 1887 they resumed the subject 

 and made a number of experiments upon the toxic properties of tin, 

 using animals. An abstract of this work will be found on page 1165. 

 Their conclusion was that tin in the stannous form, the one in which 

 it occurs in canned foods, is capable of causing disturbance, more or 

 less grave, when swallowed, and that chronic tin poisoning might pos- 

 sibly occur. They also proved that tin present in food in an insoluble 

 form was dissolved and absorbed during digestion. 



GREENING VEGETABLES WITH SALTS OF COPPER. 



Copper in varying proportions is found in many samples of canned 

 goods. It is derived to some extent from copper pans and other uten- 

 sils of the canneries, and to some extent it is added directly in the form 

 of soluble copper salts. Its natural occurrence, at least occasionally 



