SWEETENED CONDENSED MILK—SEALING 15 
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 nsually 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 copper. 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 ts 
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 zine 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- 
tion is not available, the factory must rely on its own generator. 
For the needs of the condensery a gasoline gas plant seems 
suitable. Gasoline gas is produced by forcing atmospheric air 
over or through a body of gasoline. The mixture of air and 
gasoline vapors forms the gasoline gas. The gas generators in 
use consist chiefly of carburetor, air pump or blower, and regu- 
lator. The carburetor usually has a series of cells, connected 
with one another by means of a system of syphon tubes. The 
