I have two small metal cylinders from who knows where. Anyway, they are
of similar size, but have markedly different densities. Idle curiosity,
but I want to know what they are.

They are both 1.000" in diameter and similar in color to steel.

The lighter piece is 0.750" high and weighs 42.46 grams. In the center of
one end there is a 0.14" diameter by 0.10" deep hole.

I calculate from this a density of about 5.07 g/cc, which leads me to
believe it is a titanium alloy. What else might it be?

(BTW, these numbers are accurate to the precision given.)

The heavier cylinder is 0.935" high and has a flat milled along its
length. The flat is 0.025" deep; that is, the distance from the opposite
side of the cylinder to the face of the flat is 0.975". It is uniform to
within 0.001" all along the cylinder. This piece weighs 163.73 grams and
is quite hard. An X-acto blade doesn't scratch it.

For this one, I get a density of 13.7 g/cc. Well, it certainly isn't
mercury! I thought perhaps it was some type of cemented carbide, but it
seems a tad light for that. Also, I placed a couple drops of HCl on one
end and left it there for about two minutes, but no discernable amount of
cobalt was dissolved. Any other ideas?

Thanks,

Jim