82 BULLETIN 908, U. S. DEPARTMENT OF AGRICULTURE. 



Table 35. — Composition of sardines (skinned mid unskinned) stored in cans for 3 and 6 



months. 



Period held. 



Water. 



1 

 Oil. 



Per cent. 



Per cent. 



52.19 



18.88 



52.67 



15.64 



55.00 



16.20 



56.00 



14.93 



56.81 



14.89 



54.68 



19.31 



56.13 



17.81 



Tin.i 



TTns~k-innp.fi fish 



3 months . . 



Do.... 



6 months . . 



Skinned fish: 



3 months . . 



Do.... 



6 months . . 



Do.... 



Mg. per kilo. 

 194 

 266 

 172 



225 



85 



145 



3 319 



1 Determinations made by E. L. P. Treuthardt, Food Control Laboratory, Bureau of Chemistry. 



2 Least detinning in any of cans examined. 



3 Worst of lot, tarnished all over and one-half surface pitted. 



The tin removed from the can varied greatly among the individual 

 cans, but in some cases corresponded to the amount of tarnishing or 

 detinning undergone by the can. The tin content of the pack of 

 skinned fish was, on an average, higher than that of the pack of 

 unskinned fish. It was observed, incidentally, that detinning is 

 reduced to a minimum when the cans are w r ell filled with oil, and 

 progresses more rapidly in cans where too little oil has been added 

 or where the fish have absorbed the oil, thus removing the protective 

 film between the fish and the can. The examination of these packs 

 showed that the corrosion of the interior of the can was progressive 

 and was more extensive in the packs composed of skinned fish. 



Apparently sulphur is equally distributed through the flesh and 

 skin of the fish and is not primarily responsible for the corrosive action 

 of the contents of the can. The blackening of the areas detinned and 

 the excrescences sometimes seen are due to the formation of iron 

 sulphid. This probably is the extent to which sulphur enters into the 

 reaction in the corrosion of the tinned plate. 



EFFECT OF AMMONIA AND AMINES. 



That the alkaline materials, ammonia and amines, are primarily 

 the cause of part, at least, of the detinning which occurs in sardine 

 cans was shown by the following experiments. 



Ammonia and amines, found in appreciable quantities in commer- 

 cial and experimental packs of sardines, increase during storage 

 (p. 70). That amines have a corrosive action on tin plate when con- 

 fined in cans has been shown by experiments 1 in which monomethyl- 

 amine of various strengths was sealed in cans and allowed to remain 

 for different periods of time. Bigelow and Bacon(3) attributed the 

 corrosion of the interior of tin containers used for canning shrimp to 

 monomethylamine. A. R6ssing(24) found the interior of cans in 

 which sterilized lobsters and codfish had been preserved for several 



1 Unpublished results on file in the Bureau of Chemistry. 



