THE PHILOSOPHY OF FLUXES. 48 
If this were really the case, it would be a very remarkable fact, well worthy 
of scientific investiga.tion. It would disturb all our tables of fusing points and the 
prevailing scientific doctrines of the relations between the solid and liquid states 
of matter. 
Soldering Fluxes. — Let us first consider the familiar cases of soldering 
fluxes. For soft soldering we may use rosin or ammonium chloride (sal ammon- 
iac) or hydrochloric acid (spirits of salt). What happens in such cases? The 
tin-man, for example, places a stock of solder and alloy of tin and lead on his 
work and applies the soldering-iron. If no flux is used the solder melted off 
from the stick forms a little ball which stands sluggishly on the tin plate and is 
ineffectual. If on the other hand, a little powdered rosin is there when the sold- 
ering-iron is applied the melted solder " runs," spreads itself with decided fluidity 
over the surface to which the rosin has been applied. The solder flows, and 
hence the rosin is fairly regarded as a flux. 
Take another case. Two pieces of brass, fitted or pressed together with 
considerable surface of contact, are to be united by soldering. If these are 
placed in the fire, bound together, and heated to no matter what temperature, 
and a piece of soft solder be applied at the boundaries of the surfaces in contact 
no solder will run between these surfaces. If, however, a solution of sal am- 
moniac, or hydrochloric acid, or chloride of zinc, be dropped or brushed against 
the edges of the joints just when the metal is about the heat of boiling water, and 
this liquid be thus made to run into the joints, a great difference is made. The 
workman now has only to carefully heat the metal to a certain temperature (pre- 
sently to be defined) when he finds that on application of the stick of solder it 
not only melts, but spreads or runs rapidly over the surface that was moistened 
by the flux; and if the operation were skillfully performed it insinuates itself with 
the fluidity of water between the joints, however close-fitting they may be. The 
fluidity thus imparted is even more decided than in the first case. 
Hard Soldering, — Whether silver soldering, or brazing, is performed in a 
similar manner, excepting that the silver or the "spelter" (a fusible brass) is 
applied in granules mixed with the flux in a state of powder, the flux in these 
cases being borax. 
The writer has had considerable experience in both hard and soft soldering 
of brass work, and after some reflection has framed the following theory : He is 
quite satisfied that these fluxes have no effect on the meeting point of the solder, 
nor even any direct effect on its fluidity when melted, and believes that their 
whole efficiency depends on their power of presenting to the melted solder a pure 
metallic surface, to which it can adhere, or in fact alloy itself more or less com- 
pletely. We know that melted tin, or lead, or zinc will thus adhere and alloy 
themselves to clean surfaces of other metals, just as mercury will amalgamate 
with certain metals. If a piece of dirty brass or copper be dipped into a bath of 
tin or lead, or the solder alloy of these, it will come out unaltered ; but if it be 
very carefully cleaned it will be "tinned " all over by them. The tinning and 
che galvanizing of iron plate further illustrates this. 
