XI. A. 4 Heise and Clemente: Tin Plate 199 



other inequalities in tin plate is of great importance in deter- 

 mining quality. Leaving out of consideration the question of 

 the purity of tin plate, it is evident that specifications should 

 require certain standards, both for thickness and for uniformity 

 of coating. 



Obviously the amount of coating necessary for good tin plate 

 will depend, to a large extent, on the service to which it is sub- 

 jected. The specifications for the United States Navy Depart- 

 ment ^* call for 5 pounds of tin per 112 sheets 14 by 20 inches 

 in size, corresponding to a coating of 1.123 grams per square 

 decimeter (0.367 ounce per square foot). According to Ser- 

 ger," a coating of 0.3 gram of tin per square decimeter of tin 

 plate (that is, 0.15 gram per square decimeter of surface) is suf- 

 ficient to make plate resistant to the corrosive influences to which 

 canned goods are subjected, and no material which had given 

 satisfactory service showed a smaller amount of tin. The few 

 data at hand in the Bureau of Science tend to confirm the con- 

 clusion of Serger and indicate that the figures given by him 

 represent the lower limit for good tin plate. For example, a 

 certain shipment of tin cans corroded so badly during an eighty- 

 day voyage from the United States to Manila that a large amount 

 of the contents leaked out. The corrosion was entirely from 

 the outside, the interior of the cans remaining bright and un- 

 spotted. There was no evidence of sea-water damage or undue 

 corrosive influence. Upon analysis the cans were found to have 

 a coating of 0.245 to 0.250 gram of tin per square decimeter. 



SUMMARY 



A number of methods of stripping tin plate without attack 

 on the iron base have been studied. Of these, detinning by 

 means of an electric current, making the plate the anode in a 

 bath of sodium nitrate, and stripping by immersion in a solution 

 of a lead salt made alkaline with sodium hydroxide (sodium 

 plumbite) can be recommended for rapid and accurate analytical 

 work. 



"No. 47 T 1 (February 15, 1912). 

 " Loc. cit. 



142765 6 



