102 SWEETENED CONDENSED MILK SEAUNG 



industry should, therefore, be regulated by law. In Germany, 

 the law requires that solder used in tin cans for food products 

 must not contain over 10 per cent of lead. 



Where the sealing is done by hand the solder is most con- 

 veniently used in the form of thin bars or wire. The wire is 

 usually bought already cut up in segments, each segment furnish- 

 ing solder enough to seal one can. In the newer types of soldering 

 machines the solder wire is automatically fed from spools. The 

 smaller the opening of the can, the less solder is necessary to 

 complete the seal. An opening smaller than three-eights of an 

 inch in diameter, however, cannot conveniently be used, owing 

 to the difficulty of filling the can with this viscous product. The 

 essential points of satisfactory sealing are: no "leakers" neat 

 work, rapid work, small amount of solder. Aside from the size 

 of the opening of the can, the amount of solder used depends 

 on the experience of the sealer. Beginners usually make an un- 

 even seal, waste much solder, and have many "leakers." This 

 is largely due to their ignorance of the proper soldering tempera- 

 ture of the coppers. An experienced sealer will use from two 

 to three pounds of solder per thousand tin cans with moderate- 

 sized openings. He will seal from fifteen hundred to twenty-five 

 hundred cans per day. 



Soldering Flux. The use of solder requires the application 

 of soldering flux, to prepare the surface of the tin for the solder. 

 The flux always precedes the solder. When the hot solder is 

 applied, some of the flux is bound to sweat through, between cap 

 and can, gaining access to the interior of the can. The common 

 practice of using zinc chloride or other similar acid fluxes, which 

 are highly poisonous, therefore, cannot be too strongly con- 

 demned. Their presence in the can may jeopardize the health 

 and life of the consumer, as well as the marketable properties of 

 the product. There are other fluxes which are absolutely harm- 

 less, and which, if properly used, give satisfactory results. Dry, 

 powdered resin, or resin dissolved in alcohol or gasoline, are of 

 this class. Ammonium chloride, while used in most tin shops, 

 is not as well suited for this purpose. 



Gas Supply. A plentiful and steady supply of gas is very 

 essential. Where natural gas or gas from a municipal corpora- 



