Solders are defined as "Soft" or "Hard" Soft solders are those witha low melting point of usually 450°F or less. Lead/Tin solders fall into this category as well as silver bearing tin solders. I believe a few in the past used cadmium as well & some may still yet. The old Eutectic (Brand) 157 was I believe a cadmium bearing tin solder first intrduced for soldering joints in stainless tubing for the Grade A Dairy industry.
Hard Solders have a higher melting temp & of course greater strength. This category includes both Brazing (Spelter) & Silver Solder alloys composed generally of Silver, Copper & Zinc (Brass). A much used one in the shop I worked in was "Easy-Flo 45" with a flow temp of about 1145°F, though I don't have it's exact composition.
The addition of a little Silver to a "Soft Solder" can indeed add some desirable characteristics but it does not put into the classification of a "Silver Solder" which normally contains neither lead or tin.
Source; Machinery's Handbook
The Eutectic mix of tin/lead is 66/34 at which temp it turns from solid to liquid all at once without going through a "Slush" & is also the lowest melt of either metal or any other combination there of. Irregardless of exact actual composition those bls which were regulated by heating & moving about were soldered with a soft solder, not a hard solder.
