78 Condensed Milk and Milk Powder 



copper may be used to advantage. In this tool the copper tip, which 

 is long and slender, is automatically heated by a current of gas pass- 

 ing through the handle and burning at the copper tip. The handle 

 of the device is connected wlith the gas and air pipes by means of 

 flexible rubber tubing. No time is lost waiting for the coppers to 

 heat and the flame can be so regulated that the temperature of the 

 copper tip is right and uniform. This is important, because perfect 

 work is impossible unless the coppers have the proper temperature. 



Machine-soldering is now gradually replacing hand-soldering. 

 The principle of the older types of soldering machines consisted of 

 revolving discs on which the tin cans were placed. The cap was 

 held in place by a vertical rod pressing on it. The solder was ap- 

 plied by hand, the hot soldering copper was held over, the groove 

 in the can while the cans revolved. This method had no particular 

 advantage over the hand soldering. There was little, if any, saving 

 of time and the quality of the work was not much, if any, better. 



There are now on the market newer types of soldering machines, 

 most ingeniously constructed and their operation in factories with 

 large outputs economize labor and time. When operated by a skillful 

 mechanic they do very creditable work. 



Solder. — The solder used for sealing should be of standard 

 composition. In this country, canning establishments are prone to 

 use a very poor quality of solder. It contains from 45: to 55 per 

 cent. lead. Lead is a poisonous 'metal ; its use in the canning indus- 

 try should, therefore, be regulated by law. In Germany, the law 

 requires that solder used in tin cans for food products must not con- 

 tain over 10 per cent, of lead. 



Where the sealing is done by hand the solder is most conveniently 

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

 already cut up in segments, each segment furnishing 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-eighths 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 



