Sweetened Condensed Milk — Sealing 101 



of this work is as yet done by hand. For this, different types of 

 soldering coppers are in use and the copper tips are heated in 

 soldering stoves or pots. Some soldering coppers have hollow 

 circular tips with a diameter equal to that of the cap used. 

 The hollow tip is telescoped b}'^ a rod which holds the cap in 

 place and the periphery of the tip fits into the groove of the 

 opening of the can, where it melts the solder. A rapid, neat and 

 leakless seal can be made with this instrument. 



Ordinary soldering coppers with a blunt point, such as are in 

 general use by the tin smith, are not very satisfactory. Unless 

 they are drawn out and filed down into a fine point, their use is 

 not conducive of neat work, progress is comparatively slow and 

 leakers are often numerous. When gas is available the automatic 

 soldering 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 passing through the handle and burning at the 

 copper tip. The handle of the device is connected with 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 rapidly replacing hand-solder- 

 ing. The principle of the older types of soldering machines con- 

 sisted 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 applied 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 ma- 

 chines, most ingeniously constructed and their operation in fac- 

 tories 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 



