S. Sumner,
Having a lab do a quantatative analysis is rather expensive and time consuming. I used to do this in chemistry/metallurgy lab. Almost any large city with an industrial base will have these labs.
Since the metal is in ingot form, someone took the trouble to melt and pour it. Look again at the readings. If marked as some % of lead (Pb) and % tin (Sn), it's common plumbers solder. Is it hard or soft? Most lead alloys will scratch with a finger nail. Linotype and babbit will not.
The easiest thing to do is make a melting point determination to narrow down the possibilities. Use your lead pot and borrow a thermocouple or electronic thermometer to see what temp it melts at. Ranges:
1. If relatively low (below boling point of water), it's Wood's Alloy used for making chamber casts and novelties. Do not overheat or it's low melting point is ruined
2. pure lead melts at slighly above 600 degrees.
3. lead-tin alloys (solder) can melt at less temp than pure lead, but will usually be between lead and tin alloys.
4. Linotype (typemetal) alloy.
5. babbit or engine bearing material.
6. Silver has relatively a high temp melting point. An electric lead melting pot won't do it.