I don't know of a list of tolerances online, I get mine from the Coin World Almanac, 1990 edition pages 339 - 342. I don't know what a Jolly is but from the context I am guessing it is something you hook to your triple beam balance to allow you to take weights in water for specific gravity measurements. While getting a specific gravity measurement isn't hard, the precision IS difficult. The first decimal place is easy and you can have a lot of confidence in it even with crude equipment. The second decimal place with consistency is a lot more difficult. The third decimal place is more trouble than it is worth. I have an analytical balance precise to .0001 grams and I don't trust my SG measurements to more than two places, and I allow .02 +/- on that second place. Overall composition of clad coins? According to the US Mint the copper nickel clad coins are 8.33% nickel and 91.66% copper. My reference shows density of copper and nickel at 8.96 and 8.902 respectively.
Yes Jolly balance http://en.wikipedia.org/wiki/Jolly_balance. I didn't realize that wasn't a household word. And what I made was more like what you said. 2 trays, the lower in water. Took a while to work out the bugs, but I now have confidence in accuracy and reproducibility. Anyway, this coin will need spectral analysis. I am looking into where to get that done for not so much coin.
