484 KANSAS CITY REVIEW OF SCIENCE. 
How, then, do the above-named fluxes act? Let us consider the rosin first. 
This is a hydrocarbon, a powerful reducing agent, and ^hich, when heated, 
combines with the oxygen of such metalhc oxides as those of tin, and thus effects 
a reduction of the pure metal on the surface to which applied. Thus the tin- 
man deoxidizes his tin plate surface, and then his solder amalgamates or alloys 
itself freely with and runs over or " wets" it. We take the liberty of using this 
term "wets" on account of its analogy with the familiar action of water which 
adheres to some surfaces or wets them, but runs off of others, such as greasy 
or dusty surfaces. This difference corresponds to the action of the solder with 
and without the flux. 
But what is the action of the ammonium chloride ? Careful observation 
enables us to answer this question. After applying the solution, the water dis- 
solving the salt boils off, and there is left behind a white coating of the salt itself. 
Then we go on applying more heat, and if we are skillful, we watch this white 
frost, and when we see it begins to dissipate by volatilizing in white fumes, we 
apply the solder before the last of it has gone. Then the solder runs, but if we 
had applied it sooner or later we should have failed. In this case we believe that 
the ammoniacal salt dissolves the tin film of oxide and forms a compound which, 
■like all other compounds of ammonia, is volatile at a certain temperature. Now 
in this case the temperature of volatilization of the flux corresponds to the melting 
point of the solder, and hence their adaptation to each other. 
As our practical readers know, especially the old hands, the use of sal am- 
moniac is now rather old-fashioned, having been nearly superseded by solutions 
of zinc in hydrochloric acid, or of the acid itself. The action of these is the 
same as above described, but more decided and demonstrable, just as they are 
more efficacious. The hydrochloric acid dissolves the oxide, and the chloride 
thus formed is a volatile salt, especially the chloride of zinc. 
In our apprentice days, when we received our first lesson in soldering to- 
gether the segments of a "staff-head" before turning it in the lathe, we were 
told to watch the brass until it became " beefy," and then apply the solder. 
What was this beefyness ? We have tested this question experimentally, and 
find that it is due to a removal of superficial film of zinc from the brass, -thus 
exposing a red or coppery surface, to which the term "beefy" may be fairly 
applied when it is hot and free from oxide. The zinc in the brass oxidizes 
more readily than the copper, the zinc oxide is more readily soluble in hydro- 
chloric acid or chlorides, and zinc oxide and its salts are more volatile than those 
of copper. Hence the preferential removal of the zinc and exposure of the beefy 
copper. 
The same beefyness is displayed in hard soldering, and may be seen even 
after the soldering is completed and the work has cooled, if some portion of the 
brass surface that was denuded by the flux was not covered by the brass solder. 
Brass tubes frequently show this. 
But why is borax used rather than chlorides, and how does it act ? To 
answer this question we must consider the chemical properties of borax. It is a 
