We all know murcury is toxic. But this wasnt always the case, and it was used extensively in at least two applications that I know about: dental work and hat making (or repair). How is/was mercury useful in those applications? Why was it choosen? When was it’s use stopped?
I know more about the toxicology side of your question than I do about the engineering side. If I remember correctly, the toxicity of elemental mercury is vastly less than that of certain mercuric compounds. Elemental, or metallic, mercury is the stuff that was used in dentistry - alloyed with other metals, I believe. Your body can’t really absorb it well enough for it to be a big hazard. This is why you’re not really risking your life, putting a thin and presumably fragile thermometer in your mouth. If it were to break, and you swallowed some Hg, you’d probably be okay - some silver juice would go through your system and end up with all that good bran fiber on the other end.
An organic compound of mercury, on the other hand, will get gobbled up by your digestion, where it will collect in your cells and poison you quite slowly and nastily. I wish I could remember the mercury compound most often implicated in Hg poisoning - I’ll look it up if I find my ecotox textbooks.
This isn’t to say that you should go messing around with metallic (liquid) mercury, because you will absorb a little, and it will eventually suck really bad. It’s just that it’s a much smaller danger than the compound(s).
Here’s a paragraph from an article by Alan Bruzel in March of 1999:
In the mid-1800’s, hat manufacturers began to use water-soluble mercury nitrate to soften, compress, and shape animal furs (a process known as felting). The outcome was skin absorption of mercury solution and inhalation of mercury vapor. Clinical signs of mercury poisoning included personality changes and tremors, leading to the English expression “mad as a hatter,” and the American term “Danbury Shakes” (from the Connecticut town where hatmaking was a chief industry). Although the Hatter is described as “mad” in Lewis Carroll’s Alice’s Adventures in Wonderland (written in the early 1860’s), he appears no more disturbed than any of the other characters, leaving it open to debate whether Carroll was describing a case of mercurialism, or caricaturing a contemporary. In any event, the link between hatmaking and nervous system damage was established by the middle of the 19th century. It wasn’t until 1941, however, that mercury nitrate was banned from hatmaking by 26 states of the United States.
Well, this site implies that I was underestimating the dangers from elemental mercury. I hadn’t considered the vapor inhalation vector:
That’s a cool site. I had no idea there were that many Hg compounds in use - so many of them in medicines! Diuretics, syphillis treatments, you name it.
Mikkelson chats about the expression “mad as a hatter” and questions if it is related to mercury poisoning.
I think the word for a mercury alloy used in dental work is amalgam - and my first link implies that the risk is quite high from them. I assume the ADA disagrees.
Early photography used mercury vapor in the process of developing an image on a glass plate.
Miners, over the many years, have used mercury in the separation of gold from ore. I ran across two elderly gents in the hills near an old mining community back in the mid sixties. They had set up housekeeping in a forty-foot trailerhome, and were working the ‘tailings’ from about twenty or so old mineshafts to augment their retirement. These two curmudgeonly old coots had a 55 gallon drum supported on two axles above a firepit. There was a rather expensive investment of maybe 20 gallons of mercury in the drum. This setup was about 10 feet and upwind from a screen door. The two old codgers could still function, and there was a wee bit of glint left in their eyes, but most of their speech was unintelligible. Poor old farts had been taking in that mercury stew on and off for 10 years. Too late to offer any real help, but a new firepit was dug in a less troublesome location.
Stories of the old photographers relate worse results to the body and mind.
Mercury in various forms has done some damage in the past.
FTR, the mercury in your dental work is an amalgram, not an alloy. A slight difference, but important.
Although it is true that an organic compound of mercury is more toxic than an elemental form, I’m not so sure that it’s ok to ingest elemental mercury. (Actually, I’d definitely recommend against it, but I don’t have the toxicological background to explain why.) Can’t the liver methylate elemental mercury? (i.e., convert elemental mercury to an organic compound) Regardless, I think the elemental form has a known/suspected toxicity too.
Not to mention its use in some vaccines. (mercury is part of the perservative…thimersol, IIRC) This is becoming a concern for innoculations given to children who may be more susceptible than adults.
I’ll see what I can dig up about the toxicology & engineering side of this topic.
Well, I didn’t mean it’s okay to ingest elemental mercury, I’m just saying a broken thermometer won’t kill you or make you insane. Or, if it will kill you, I think those things should be labelled better. :eek:
And by the way, I shouldn’t have blandly referred to the most dangerous Hg compounds as “organic” - plenty of them are inorganic (or else I can’t see any carbon references in their short names).
Yeah, my link confirmed this. I’ll no longer refer to elemental mercury as “relatively innocuous”, since it gives the wrong impression. I’ll just say the compounds are “even worse” than the element.
But you’ve jogged my memory - the organic I was thinking of is methyl mercury. A real monster of a poison. Worse than french fries. If the liver can methylate quicksilver, than that would partly explain some of the toxicity … otherwize I wouldn’t expect something to have great systemic toxicity unless it were water- or lipid-soluble.
Okay, so let me guess (guessing is a stand-in for a good memory) and amalgam is a solution, but the solvent is a solid, and the solute can be a liquid? Or is an amalgam wholly different from a solution?
And an alloy is never a solution?
Are there any mercury alloys at all, or only amalgams? (So many metal questions, so little time.)
OK. The first thing I have to do is not mis-type the word “amalgam”. So everyone pretend like I didn’t hit that little “r” at the same time I hit the “g”.
An amalgam is defined specifically as alloys that mercury forms with other metals - in fact, mercury will form an amalgam with most common metals except iron and platinum. Thus, an amalgam is just an alloy of mercury with another metal. At least, that is what my materials science reference books tell me. “dictionary.com” lists an alternate definition of being “applied to soft alloys generally”, without specific mention of mercury.
Now, as to the OP:
According to a paper I once read, mercury first was used for fillings in 1826. It was combined with various other metals (silver and copper) to create a filling material by a dentist in Paris, who was looking for a better material for filling teeth. In 1833, the use of mercury in dental fillings was being discussed throughout the World (although gold was still used for most fillings), and due to the relative inexpensiveness of the silver-mercury amalgam and the high cost of gold, it’s use caught on incredibly quickly. By 1840, it was in common use by dentists on the East coast of the US.
Another big advantage of using mercury is that it required much less skill to implement, and was easier to use for large and complicated fillings. It is also somewhat harder than gold, and thus much more durable.
Although some dentists questioned the use of a poison in a dental application, they were swayed by the ease of use and low cost of the material. A common debate that would ensue was whether or not the patient would suffer more health problems from not getting the fillings put in, as opposed to getting them put in. It is also worthy to note that the use of silver-mercury amalgam fillings allowed the less affluent to start to receive affordable dental fillings for the first time in history.
The “mercury fillings are killing us” hoopla is being fought by the ADA. (Of course, it was supported by that tabloid-in-newsman’s-clothing, 60 Minutes, in the early 90s. But they showed people being “miraculously cured” of different ailments the morning after their mercury/amalgam fillings were removed. Since all metal poisoning occurs over time and requires time for recovery, this was a clear example of minds-over-matter that 60 Minutes should have seen as a warning sign that their show was nonsense, but they broadcast it anyway.)
I don’t know anything about mercury in dental work, but can go on (for far too long, I’m sure) about mercury hazards in general (and I will get to thermometers and Mad Hatters)
First, just a comment on the danger: Probably the most dangerous effect of mercury is that even in very small doses, it can seriously affect development in fetuses and small children – we’re talking permanent lifetime damage here. This happens at levels far, far below that at which an adult whould be affected.
The other significant thing about mercury is that it never goes away (being an element and all). So mercury in the trash often gets incinerated, and thereby spewn into the air. It lands in a stream somewhere, bacteria in the stream turn it into really dangerous methyl mercury, the methyl mercury accumulates in fish, a pregnant women eats the fish, and you get one very unhappy baby. Almost every river and lake in the Northeast U.S. (downwind from the rest of the country) now has enough mercury accumulated in it that pregnant &nursing women and children are advised to limit the amount of fish they eat from those water bodies. Ocean fish like swordfish can also have enough of a dose for concern.
Because of these two factors, public health and environmentalists are trying to pretty much get rid of every use of mercury, as that’s the only way to get rivers clean again (eventually). I don’t know anything about fillings, but a major target for mercury reduction is thermometers and other medical uses (such as spyg- sphigno- sphygno- uh, blood pressure thingys, mercury containing bleaches, lab reagents, etc.). Some states and cites have already banned the sale of mercury thermometers, and there are probably going to be more bans like that in the future. the concern is both the health of the user, and the overall environmental concerns (which boil down to the health of fish eaters, etc.)
Finally, to address Boris B’s comment that Mikkelson questions the ‘Mad Hatter’ = mercury poisoning derivation, the consensus when I asked that question a week ago http://boards.straightdope.com/sdmb/showthread.php?threadid=51758 was that Mikkelson/Snopes was a little too cautious – the connection seems pretty well supported.
All in all, being the March Hare seems a lot more fun way to go crazy, though.