Science desk
< February 5	<< Jan \| February \| Mar >>	February 7 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

February 6

Purification

I'm experimenting with fractional electroextraction as a means of non-specific metal recycling. The process is as follows:

Digest the raw material in hot concentrated sulfuric acid, and allow to liquor to settle.
Decant the liquid portion off from any remaining solids.
Electroextract the decanted liquid at 4.5 V, and 100 mA, using a graphite cathode, and platinum anode.
Redissolve the deposit in concentrated hydrochloric acid.

This yields a metal concentrate in the form of a chloride, which can be reprocessed at voltage intervals according to the fractional model. The issue is the chloride concentrate is invariably contaminated with assorted sulfates, and carbon from the cathode. I need to find an efficient way of removing the sulfates (I can remove the carbon by simple filtration methods). I need a second opinion on an idea I have yet to try.

I plan to add either strontium chloride or strontium carbonate, which should absorb any sulfate. I should be able to filter it out from a chilled solution. However, I want to recover the strontium, so I will need to process it to remove the sulfate. I plan to react it with a solution made from ammoniated soda water - aqueous ammonium carbonate. Strontium carbonate is insoluble and can be filtered off, while the ammonium sulfate can be disposed of. How quickly should strontium sulfate, which is considered insoluble, react with ammonium carbonate? Plasmic Physics (talk) 12:24, 6 February 2015 (UTC)[reply]

Add barium chloride, and you'll precipitate barium sulfate. Strontium would work too, though barium sulfate is a lot less soluble than strontium sulfate, and you want to get as much out as possible. According to the data in the Wikipedia articles, barium sulfate is about 2 orders of magnitude less soluble than strontium sulfate. --Jayron 32 14:57, 6 February 2015 (UTC)[reply]

Barium compounds are probably cheaper than strontium, but the whole process does not sound low cost, barium carbonate could be precipitated the same way. The insoluble carbonate formation will be immediate, as soon as the solutions are mixed. But the result may be very fine and just take ages to settle out, or go through the holes in your filter paper. Graeme Bartlett (talk) 21:44, 6 February 2015 (UTC)[reply]

Perhaps he could use a centrifuge to remove the powder instead of filtration. --Jayron 32 23:14, 7 February 2015 (UTC)[reply]

OK, but I actually have strontium carbonate. If I'm going to use barium chloride, I'll have to buy it. Where can I find temperature/solubility information for strontium and barium sulfates? And how are their solubilities affected by exchanging water as the solvent for a brine solution? Plasmic Physics (talk) 03:36, 7 February 2015 (UTC)[reply]

Are gonanes steranes?

The German article says they are, but in the English articles, they look very different. Aside from the side chain at C-17 (which varies according to the English article, and may conceivably be just H), the English sterane also has C-18 and C-19. — Sebastian 13:46, 6 February 2015 (UTC)[reply]

The images inserted into an article are often repurposed from some other intended use, so should be taken skeptically. Looking at [1] [2] I'm seeing a 17-carbon basic sterane backbone numbering. (Admittedly the first source would be more credible if it weren't a sterol they showed, though) On the other hand, a compound name like "C29 5A,14B,17B,20S-Sterane" seems to imply structure for no less than 29 carbons. So there's some specialized steroid chemist nomenclature around this. On impulse I searched "C17 sterane" and came up with hits describing this basic core. I don't know if sterane has a defined "default" length when used to name a specific molecule, or if it only exists as the designation for a class of compounds. Wnt (talk) 14:02, 6 February 2015 (UTC)[reply]

Humorous description of paleontology/the fossil record

I recall once reading a sardonic description of the fossil record, or the whole discipline of paleontology, as something along the lines of "a succession of teeth that give birth to other teeth." Unfortunately, I can't recall the wording well enough to Google it, nor do I have any idea what the source is. Anyone know what I'm talking about? 75.4.22.29 (talk) 14:45, 6 February 2015 (UTC)[reply]

My first instinct is to say this quote came from The Record of the Rocks, which is one of the first chapters in A Short History of the World. The e-text at Project Gutenberg does not contain this quote, or anything like it... but there have been many editions. I will check my paper copy and report back. Nimur (talk) 16:35, 6 February 2015 (UTC)[reply]

...No, this quote is not in my 1940 edition of the Outline of World History, although "teeth" show up in the index for several chapters - including the discussions of the early evolutionary fossil records. Nimur (talk) 16:51, 6 February 2015 (UTC)[reply]

The quotation is from Alfred Romer's 1968 book Notes and Comments on Vertebrate Paleontology (page 161): the full text is "So great has been this concentration on dentitions that I often accuse my 'mammalian' colleagues, not without some degree of justice, of conceiving of mammals as consisting solely of molar teeth and of considering that mammalian evolution consisted of parent molar teeth giving birth to filial molar teeth and so on down through the ages." See here for one of the numerous references available. Tevildo (talk) 23:08, 6 February 2015 (UTC)[reply]

Thanks, that sounds like what I had in mind! I'm glad that someone here knew what the heck I was talking about. 75.4.22.29 (talk) 01:37, 7 February 2015 (UTC)[reply]

Resolved

Is lead solder wire unhealthy for the user of it or for the environment?

Is lead solder wire unhealthy for the user of it or for the environment?--Noopolo (talk) 16:36, 6 February 2015 (UTC)[reply]

The general consensus is that it is unhealthy, but opinions differ on exactly how bad it is for you. Most reputable consumer-electronics manufacturers have either voluntarily opted to eliminate lead solder, or have been required to eliminate it, as part of the Restriction of Hazardous Substances Directive that govern sale of electronics - particuarly for sale in Europe - though most American manufacturers and their far-East contractors also comply with this directive.

Electronics manufactured for markets in Asia, Africa, and India are more likely to be built in factories that still use lead solder. Regrettably, even our Wikipedia article lacks great information on RoHS impact to those regions.

Nimur (talk) 16:42, 6 February 2015 (UTC)[reply]

When soldering electronics, flux vapors seem to be the main concern. See this advisory: http://www2.lbl.gov/ehs/ih/pdf/safeSolderingFinal.pdf

I still use tin-lead solder, the 1.5 kg I have left will last me a lifetime. Ssscienccce (talk) 21:13, 6 February 2015 (UTC)[reply]

That may be a self fulfilling prophecy. Greglocock (talk) 21:49, 6 February 2015 (UTC)[reply]

The amount of lead a person would ingest from the act of soldering is likely minimal, but the tendency is to bar almost all uses of lead other than in car batteries - which end up losing a lot more lead than any hobbyist doing soldering could imagine. We also bar "lead soldiers" although no one has found much evidence evidence of children being poisoned by them[3]("Although department spokesmen say none of the state's thousands of annual cases of lead poisoning has been attributed to model soldiers"), while lead acetate in paint definitely caused problems as children found it to taste sweet. Fumes from lead molding kits was generally far greater a problem than the wonderful Britains soldiers. Collect (talk) 22:01, 6 February 2015 (UTC)[reply]

That is a horribly irresponsible, quite utterly misleading answer - and it's flat out wrong. Please check your references before giving such ridiculously dangerous advice - especially on a medical matter - and double-especially where children are involved. There is no excuse for getting this wrong. Our Lead and Lead poisoning articles are quite clear on this - and you should have at least browsed their introductions before posting anything on this matter!

Lead poisoning isn't an all-or-nothing thing. Any level of exposure has some effect. Our article on lead says: "Lead has been shown many times to permanently reduce the cognitive capacity of children at extremely low levels of exposure". Your reference is a newspaper article - and there is a reason why Wikipedia doesn't accept such references where medical matters are involved (See: WP:MEDRS. Our articles refer to an 11 year study with very low dosage levels...and it's findings are incontrovertable. Which means that playing with lead soldiers as a child will certainly have reduced your IQ - perhaps not by much, perhaps considerably...you'll never know. There is no 'safe' level of exposure - small amounts cause small amounts of cognitive loss, larger amounts cause more...and it's cumulative in effect, so the more interaction a child has with lead in their environment, the worse the outcome will be. The newspaper report talks about "the number of cases of lead poisoning" - but that can't mean "the number of cases where a child lost 10 IQ points" - because those will never be noticed, never reported to healthcare workers, never result in a hospital visit - and therefore never be recorded as lead-poisoning-due-to-lead-soldiers. It also talks about "unhealthy levels of lead" - which isn't a very meaningful concept for a poison that is cumulative and has no "safe" level. Any amount of lead is 'unhealthy' - it's just a matter of degree.

That said - the problem with toy soldiers is mitigated by the fact that people generally paint them with enamel paint. That goes a long way to reducing the exposure to the lead beneath. But with old toys, and much-used gamer figurines, and toys that get much abuse - the paint will gradually wear thin or perhaps flake off - and at that point, the responsible thing to do is to touch up the paint. Another issue is with children who get into this hobby and paint their own figurines - resulting in much exposure and handling of unpainted and semi-painted models. A responsible parent should give each figurine a good shot of flat white aerosol primer before the child handles it (that actually makes the paintwork more vibrant - so it's a good idea anyway) - and a shot of some kind of flat sealant after the painting has been done to protect the paintwork in future. Fortunately, there is an increasing trend in the manufacture of these figurines to reduce the amount of lead in favor of adding more tin - and increasingly, people are using resin-cast and even 3D printed ABS figurines. So even this level of exposure is gradually fading away.

(NOTE: My wife and I are active in the very gamer communities where these figurines are used - and my wife's home-business (http://RenaissanceMiniatures.com) is making product for the very people we're discussing. Our business interest is to encourage gamers - but our ethical response is to warn about the dangers of lead exposure.)

The other issue is this 'cumulative' thing. Giving children a dose of lead from toy soldiers (or soldering electronics, lead paint, or whatever) reduces their ability to cope with future lead contact. This damage doesn't repair itself - some the lead stays in their system for life (it gradually builds itself into their bones) - so there is no recovery from even the lowest dose levels.

So, the correct answer here is to strenuously avoid lead contact for children, and to a lesser extent for adults. Do not take this lightly. The symptoms will be unlikely ever to manifest themselves in ways you'll notice. But if you'd like your children to grow up to be as intelligent as they possibly can be - then avoiding even low levels of lead exposure is the responsible thing to do. The difference between an SAT score of 1100 and 1300 is a likely post-graduation salary of $60,000 to $130,000. So every SAT point is worth on average around $350 a year to your child in the future. That means that even low levels of childhood lead intake will have a material effect on their future - even though you'll never know how much.

This is why your answer is both dangerous and irresponsible.

SteveBaker (talk) 16:10, 7 February 2015 (UTC)[reply]

Thank you - but I relied on what the current sources state. And the "even an atom will kill you" approach is unwise - the amount of lead in lead batteries is greater than any other use. [4] By the early 2000s, the total demand for lead in all types of lead-acid storage batteries represented 88% of apparent U.S. lead consumption. Other significant uses included ammunition (3%), oxides in glass and ceramics (3%), casting metals (2%), and sheet lead (1%). The remainder was consumed in solders, bearing metals, brass and bronze billets, covering for cable, caulking lead, and extruded products. In short all other uses amount to about 1% of all lead use. Most commercial soldering is done in special machinery from which lead exposure to workers is de minimis. Lead solder wire is considered a safe product for adult use.

It is not expected that occasional soldering activities that take place within areas that are well ventilated or have additional local exhaust ventilation will pose an occupational hazard to the employee. However, it is prudent to implement best practices regardless of the frequency and duration of soldering. [5] Cheers.

And stay away from lead-acid batteries and ammunition. We no longer use lead-based paints, or tetraethyl lead in gasoline - by far the two greatest uses associated with lead poisoning. 25% of the housing stock may still have some lead-based paint, a significant concern. [6] does not even consider solder a significant risk at all. Am I telling people to eat lead? No way. Am I telling them to recognize the actual level of concern? Yes. And is that level of concern different for adults doing casual soldering and children casting lead figures? Way yes. Looking at another issue in the news - is there any conceivable ill-result from vaccines? Yes. Is that of a level where children should not get proper vaccinations? Hell no. Cheers. Collect (talk) 20:19, 7 February 2015 (UTC)[reply]

I can accept that very low levels might still cause harm, but not that there is absolutely no safe level. After all, some lead is naturally in the environment. So, we can't just say that any lead exposure, even one atom, is dangerous. It's important to weigh the relative risks of each material and rate them realistically. Otherwise we might get people switching to more dangerous materials, and that would be irresponsible.

One place where I think we should eliminate lead is in bullets and shells. Copper works almost as well, and doesn't poison the environment and animals that eat animals killed with those bullets and shells. The difference in toxicity is one factor, but also copper bullets don't fragment the way lead does. StuRat (talk) 16:33, 7 February 2015 (UTC)[reply]

When I worked in industry, we had production lines with women soldering with 60/40 all day long – not a good thing- knowing what we know now. Lead poising can be subtle and difficult for a doctor to diagnose correctly and not to contribute symptoms to other maladies but damage is being done never the less. Copper is both expensive and toxic too. There are better alternatives to lead when blasting away at cute little critters Shot_(pellet)#Non-toxic_alternatives_to_lead_shot.--Aspro (talk) 18:46, 7 February 2015 (UTC)[reply]

Unlike lead, copper is a necessary nutrient. You can overdose on it, but the same is true of iron, which is one of the items in your list. Also, the tungsten-bronze shot pellets listed are up to 44.4% copper, so obviously they aren't concerned with copper toxicity in the shot. StuRat (talk) 22:06, 7 February 2015 (UTC)[reply]

I don't want to take away from the anti-lead message, because as far as I can tell from the data cited [7] is pretty good that more than about 0.5 micromoles/liter of blood (about 0.2 milligrams of lead for a small child with, say, two liters of blood/interstitial fluid, perhaps - I'm guessing here) is already potentially problematic and could take weeks to clear or become fixed in the bones. Still, technically it is a correlation - though one well controlled for socioeconomic and other factors - rather than causation. To give an example of what I mean (this is not accepted medicine) it is thought that lower melatonin might increase susceptibility to brain injury [8] and melatonin also helps to clear lead from the blood [9]. So I won't rule out that, to some limited extent, it is some innate trait of the child that creates/preserves intelligence that reduces lead level, and not just the other way around. ;) Wnt (talk) 20:19, 7 February 2015 (UTC)[reply]

I solder from time to time. I have no hard information to base my habits on but I play it safe and use a strong fan. If I smell the fumes I exhale and move away from the area. I am a bit paranoid about toxins though. Lead scares me a lot because it damages intelligence and I like my intelligence. Chillum 22:10, 7 February 2015 (UTC)[reply]

I figure I'm dumber than I was forty years ago when I started soldering but don't know whether heavy metal is part of that. Of course, this failure may be caused by a poisoned brain, but I didn't solder every day or week or month or even every year, so it's probably just a matter of a mind going stiff with age. Never soldered in my last 10 years before retirement, and seldom did in the previous 10. Jim.henderson (talk) 16:53, 10 February 2015 (UTC)[reply]