So, my boss wants to sell me a machine that he doesn't need, is just sitting in the cabinet collecting dust, and I could make use of it. Market value is about $650, he'd sell it for $300.

Problem is, I am told by another employee who has been here longer than I have, that I it doesn't really belong to him, it belongs to another employee, who died in 2009. This man's wife and heir moved away afterwards and it's not really known where she went, but no effort was ever made, to the other employee's knowledge, to track her down. She may not have known she had possessions at her husband's work. But she might not have cared, either, as she evidently made no efforts to check into the matter. We still use another machine he left here, which is worth about $4500, every day. We are not talking something really expensive like a car that would justify a big effort to find the rightful heir, but neither are we talking some $5 trifle either.

Does uncontested possession for 7 years make for ownership of something?

Is the ownership actually known or is it office lore?  In my experience, there are sometimes items that are used in the shop that "everyone knows belongs to so-and-so" but more because he is the one who convinced the boss to buy the item, used it, and kept it in good working order.  The items really didn't belong to him in a legal or even moral sense, but heaven help anyone who took the item out of it's storage location and used it!

"We still use another machine he left here, which is worth about $4500, every day. We are not talking something really expensive like a car that would justify a big effort to find the rightful heir, but neither are we talking some $5 trifle either."

Which is it? You just contradicted yourself.

A) "We still use another machine he left here, which is worth about $4500, every day."
B) "We are not talking something really expensive like a car"

Uh... newsflash buddy. LOTS of cars are priced well under $4500.  In fact, $4500 would purchase BOTH of our family vehicles. Our 1999 Suburban, as well as our 2001 PT Cruiser.

And how about we judge the value of these items in terms of the widow's monthly income? She's probably scraping by on Social Security and if she got $30 more per month, she'd feel like she was living in luxury. She'd be able to buy ice cream again and have dessert every 3 days or something... Maybe if she got that "windfall" she didn't know she had, she'd be able to do something really decadent like replace her broken toaster.

It sounds like you're trying to justify this. I'd say you need to try to track down that widow -- especially to get $4500 from that company for her husband's equipment. And then give her back that $650 "machine" as well, or buy it from her. But I'll guarantee you a widow could use $4500.

It appears that the machine in question was abandoned. Your employer has a right to sell the machine.

OP here. I'll try to answer everybody's questions. In a white collar office it would be unheard of for an employee to be expected to supply their own computer or stapler, but in the blue collar skilled tradesman world it's pretty common, maybe even happens more often than not. A guy doesn't like the equipment supplied, or there is no equipment supplied of the type he needs to do his job, so he uses his own tools, which can sometimes be high dollar. Mechanics do this a lot too. The machine I mentioned that we use every day, is a milling machine, which is used to cut and shape metal. The machine offered to me for sale is a piece of testing equipment, which doesn't meet the latest European standards, so isn't useful to the company any more because they can't use it for big corporate contracts, but it would be very useful for a guy wanting to do some work on the side for himself. Obviously as a traditional catholic, money isn't growing on trees so being offered something at better than half price is very tempting. I can't come out and ask if he has the moral right to sell me this, because that's just not the kind of thing you can ask your boss, if you want to continue to work somewhere. He also might not know himself because he inherited the business from his brother, who is also dead.

I asked a couple of guys about the tools. Everyone is pretty sure the milling machine (that's the $4500 one) did belong to the dead employee. As for the other tool, the one that directly concerns me, one guy thinks it belonged to the dead man, one guy didn't know at all where it came from. (But he's 84 and I don't think his memory is what it used to be. He's worked here for 25 years though so might be expected to know.) I'm personally now inclined to just buy it and not worry. Its a good deal, and the same rumor mill that said that these started out as the employees personal property also says that his widow was very well off and planned to travel the world after he died, that he made over $100,000 a year and did a lot of successful speculation on the stock market, and nobody knew for sure if the widow knew about the tools, cared, or maybe the boss bought them off her or she just let the matter drop since evidently his death took place several states away. So why assume the worst? After 7 years it's pretty clear nobody is going to come looking for them, the people who knew for sure may well be dead,  and if I bought the one, it could do some good.

Sorry for writing a book lol. To sum up:  Sometimes in machine shops employees bring their own tools to work. I don't want to ask my boss if he's sure the machine didn't rightfully belong to dead employee's heirs, because that obviously implies that I don't trust him or can come off as an accusation, but I asked around and nobody knows for sure, and it seems that probably the only people who know for sure are dead. So why assume the worst of my boss?

1.  Maybe the owner bought it from the widow, or had an arrangement where he paid for part of the funeral.  All you know is that it was owned by some other guy, at some point.  If you don't have facts to support an immoral situation, you have to assume it's legit.

2.  It's not your responsibility to make amends between a former employee's family and the owner, if amends are even necessary.

3.  If you want to buy the equipment, then buy it.

4.  Have a mass said for the former owner, if it makes you feel better.

To remain willfully ignorant in order to buy the equipment is a mortal sin.  But a person can also be unreasonably scrupulous.  Why not do a brief Internet search for the deceased  man's widow or children.  If you find one, ask.  If a search turns up nothing, go ahead and buy it. If you "just can't decide," consider the situation a distraction and move on.  Let its disposal be your boss's problem.  There are much more important things in life than getting bogged down in whether or not to buy a dead man's equipment.