Wikipedia:Reference desk/Archives/Science/2017 November 11

= November 11 =

Salicylic acid and acetylsalicylic acid
What difference would it make if we took the first, instead of the second, for a headache?--Hofhof (talk) 01:06, 11 November 2017 (UTC)
 * Salicylic acid (medical use) would burn the inside of your mouth and throat. -Arch dude (talk) 04:21, 11 November 2017 (UTC)
 * And yet the ancient Greeks used it (in the form of willow bark) for headaches with no apparent ill effects. 2601:646:8E01:7E0B:0:0:0:EA04 (talk) 10:12, 11 November 2017 (UTC)
 * Sola dosis facit venenum! Rather a difference between concentrated solutions and small amounts in bark. Fgf10 (talk) 11:47, 11 November 2017 (UTC)
 * It's workable (and has a long history) to use salicylates from willows, but it's slightly unpleasant on the stomach. It was usually taken as a tea, made directly from the willow bark.  Any more concentrated form of salicylic acid (see above) is wart remover and isn't consumed internally.
 * Nor is it a question of dose, it's a different compound. In fact, salicylic acid is so harmful that it wasn't taken directly (there was a brief Victorian period when it was, as it was much cheaper). The compound prepared from the tree is a sugar called salicin, and that is oxidised within the body to the acid form. However it's hard to produce large quantities of salicin cheaply. Salicyclic acid was only taken as a drug for a brief period after the development of industrial pharmacy, when salicyclic acid could be synthesised cheaply, without willows, and before the mighty Bayer of Germany invented Aspirin as a more acceptable form of it.
 * Charles Frédéric Gerhardt, one of the illustrious group of self-poisoning chemists, had first set out to synthesise a more acceptable form of salicyclic acid and found that acetyl salicylic acid was suitable. However his synthesis wasn't very good and he gave up, thinking that the compound was wrong, rather than it just being his process. It was some decades before his original work was really proven to be right, by Felix Hoffman at Bayer.
 * Note that WP's claim, "Aspirin, in the form of leaves from the willow tree, has been used for its health effects for at least 2,400 years." is just wrong (and a complete misunderstanding of a childishly simple and correct ref). But that's GA review and MEDRS for you - form over accuracy, every time. Andy Dingley (talk) 12:06, 11 November 2017 (UTC)
 * That claim was not supported by the source, so I've changed it.   D b f i r s   12:54, 11 November 2017 (UTC)
 * First, salicylates have been used for at least 5000 years, as evidenced by Ur III, a tablet from Ur of the Chaldees from, if I recall correctly, roughly 300 years before the birth of the biblical patriarch Abraham. Here's one source.   Salicylate was available in other forms - beaver testicles notably concentrate it in a way that they would apply to toothaches and such, and were used by native Americans; there was even a myth in Europe from classical times that the beaver would castrate itself when hunters grew near to avoid capture. (see Tractatus de Herbis)
 * Second, the willow bark salicylates used 5000 years ago were far safer than the only ones allowed to be sold over the counter by responsible medical authorities today.   This is because salicin comes as a glycoconjugate that is not taken apart until after it passes through the stomach.  By contrast, aspirin was invented a century ago by industrialists who noticed that the salicylates they sold were causing stomach injury, and who figured it was due to the acid, so (after first trying to "buffer" the acid, e.g. Bufferin) they put a simple acetyl group over the acid hoping to stop the damage.  Same folks who brought you heroin as the non-addictive alternative to morphine (a racket that works to this day). Wnt (talk) 16:50, 11 November 2017 (UTC)
 * Thank you for that earlier history. I've added a brief mention to the article.    D b f i r s   18:33, 11 November 2017 (UTC)


 * As willow bark has been mentioned, I think I will have a go at a bit of clarification. Pharmaceutical companies love to synthesize   the most active component of any proven natural remedy and market it.  Willow Bark contains  salicylic acid but the 'therapeutic' dose of Willow Bark has far less salicylic acid per dose, so does not cause the same problems as therapeutic dose of pure  salicylic acid nor  acetylsalicylic acid. The reason for this is that Willow Bark also contains other compounds that work synergically, which enhance the therapeutic effect of the little Salicylic acid that Willow Bark has per dose.  This is why many users of Willow Bark swear blind that it is more effective than drug-store  bought acetylsalicylic acid pain killers. Placebo? Doctors take it rather than become dependent on anything stronger and addictive. Also many doctors are closet alcoholics. So even though Willow Bark is far from completely safe for a habitual drinkers is better than acetylsalicylic acid, acetaminophen, ibuprofen, naproxen, etc.  These drugs do the kidneys in quicker. Yet, since one's HCP can't earn money from writing 'scripts for Willow Bark – one ends up being proscribed  a synthetic. And why not. Your Doctor  is running a business and he too, has to earn enough to put his kids through collage – and possible be the first in the street to own a Tesla  etc.. Aspro (talk) 23:15, 11 November 2017 (UTC)
 * I wonder whether there are collage colleges. Akld guy (talk) 06:14, 12 November 2017 (UTC)


 * Rather than take the acid, why not consider the conjugate base of salicylic acid: in the form of something like Sodium salicylate? That avoids the rather obvious acid problem. Our current Sodium salicylate does suggest a set of therapeutic uses. Klbrain (talk) 01:27, 13 November 2017 (UTC)
 * That was the idea behind "Bufferin", but it was generally incorrect. I think it is more accurate to say that cyclooxygenase enzymes (especially COX-1) in the stomach are needed to prevent injury, and if salicylate is absorbed there it will inhibit those enzymes. Wnt (talk) 22:37, 14 November 2017 (UTC)

where can I find literature on anhydrous acid-base equilibria?
It is really frustrating to me as a tutor of organic chemistry that everyone assumes that acid base reactions always take place in water. I need more information about how to estimate pKa of an organic compound in say, ethanol or glacial acetic acid, given a pKa in water and pKb of a conjugate base (and vice versa), as well as the autoionization constant of the target solvent. Also, how would I calculate the change in pKas for polar aprotic solvents? 98.14.205.209 (talk) 15:41, 11 November 2017 (UTC)
 * It might not be a solvable problem at this point. Acid_dissociation_constant is our main article, and its "Acidity in nonaqueous solutions" section notes:
 * These facts are obscured by the omission of the solvent from the expression that is normally used to define pKa, but pKa values obtained in a given mixed solvent can be compared to each other, giving relative acid strengths. The same is true of pKa values obtained in a particular non-aqueous solvent such a DMSO.
 * As of 2008, a universal, solvent-independent, scale for acid dissociation constants has not been developed, since there is no known way to compare the standard states of two different solvents.
 * The following ref (cited in that article section) has some information about comparing pKa in different solvents, especially with respect to different structural classes:
 * DMacks (talk) 16:31, 11 November 2017 (UTC)
 * DMacks (talk) 16:31, 11 November 2017 (UTC)
 * DMacks (talk) 16:31, 11 November 2017 (UTC)


 * (ec)It appears that despite the deceptively simple looking equilibrium, pKa depends on both the solvent and the ionic strength .  That IUPAC source mentions Davies equation, Debye-Huckel theory, Pitzer equation, Specific Interaction Theory.  The pKa also depends on temperature in a way that varies based on the class of compound, yet follows some empirical rules within them.   Certainly I don't know this topic, but I should put these up to get started. Wnt (talk) 16:32, 11 November 2017 (UTC)


 * OK thank you, because I am trying to define the scope of problems that I can cover with my students, and in many cases I have to know much more than my students would need to know (to ace their exams) because their education (and mine) I realize sometimes seem to side-step certain problems with dogmatic assumptions. 98.14.205.209 (talk) 16:38, 11 November 2017 (UTC)

Systems of acid and non-conjugate base (e.g. ammonium bicarbonate, pyridinium dihydrogen phosphate, boric acid - acetate)
Why aren't systems like these covered as extensively in online pages? Almost every web page seems to stop at adding a strong base to a weak acid or strong acid to weak base which is *really frustrating*. I suddenly realize that we didn't really cover many non-conjugate buffers in undergrad (the most we did was ammonium acetate, which to be honest is CHEATING since pKa + pKb = 14 and is really just a hidden version of the acid / conjugate-base problem). Basically we have a weak acid and a weak base whose pKas and pKbs do not add up to 14. Surely there must be a better way than having to brute force it through a system of equations? 98.14.205.209 (talk) 16:34, 11 November 2017 (UTC)
 * The reason that things are covered less is because no one wrote about them. However that may be because the topic is not WP:Notable in itself.  For example if I look for "pyridinium dihydrogen phosphate" nearly all hits are derivatives. The one that was not was an error. That suggests that it is not useful compared to anything else already known. Ammonium bicarbonate however is used as a buffer and there are numerous references as to its use. eg https://www.nestgrp.com/protocols/trng/buffer.shtml and a buffer calculator at https://www.liverpool.ac.uk/buffers/buffercalc.html Graeme Bartlett (talk) 22:00, 11 November 2017 (UTC)
 * Boric acetate is used as a buffer in this patent. SciFinder has about 10 hits for "pyridium phosphate", the result-set of which is annotated as being an uncertain ratio, and seem to have been studied as corrosion inhibitors. DMacks (talk) 22:21, 11 November 2017 (UTC)
 * TBE buffer is quite common in molecular biology - TAE buffer less so, but not unheard of. (The EDTA is just a preservative; these are between Tris (pH 8) and borate or acetate. Wnt (talk) 11:46, 12 November 2017 (UTC)

AXLE FLUX GENERATOR OUTPUT.


The permanent magnets used in constructing Axle Flux Generators are always arranged to have alternate poles such as: N-S-N-S-N-S etc. What would be the effect on the output waveform if I used similar poles such as: N-N-N-N-N etc. — Preceding unsigned comment added by Adenola87 (talk • contribs) 16:59, 11 November 2017 (UTC)
 * An axial flux generator? The usual source for building advice on these (small scale wind turbines) is Hugh Piggott's books or website. You need to alternate the magnets, so that there is a changing flux through the coils. If there is no change of flux, then there's no output.
 * A long-established design is the claw pole alternator. This uses a single field coil (so the flux in the armature is always the same direction) and has sets of interleave pole pieces from each end, so that it has the effect of a reversing field. Andy Dingley (talk) 19:10, 11 November 2017 (UTC)
 * I assume you mean axial flux. There's not much to be had with novel configurations compared with state of the art, you can buy off the shelf axial flux motor kits for a couple of thousand dollars that are 97% efficient. http://www.ata.org.au/wp-content/uploads/marand_high_efficiency_motor.pdf The CAD drawing on P9 of that presentation was my original package layout from 1994/5.  Greglocock (talk) 19:23, 11 November 2017 (UTC)

Rifles with horizontal magazines
Unlike most guns with box-like magazines, some have cartridges kept in horizontal pipe-shaped magazines fitted just below their barrels (mostly clutch-action "lever-action" or "pump-action" rifles). Such an arrangement may be all a right for shotguns which always use cartridges with flat front-ends, but in the rifles the cartridges' front end is never flat, it may not be sharp ( like AK-47s etc.), and is rounded to some extent, but is still narrow enough to work as a fire-pin against the front-to-it cartridge lying with its most sensitive part (cap) just touching it (bullet-tip of the neighbor behind). Is this arrangement not considered risky ? Besides the gun may also receive some unexpected jerk etc. ?  Jon Ascton    (talk)  17:25, 11 November 2017 (UTC)
 * It's called a tube magazine, and it's used on lever-action rifles like the Winchester Model 94. There are a lot of videos of people fooling around with this configuration trying to set off a chain reaction in the tube. Conventional wisdom is that pointy bullets are dangerous in tube magazines, and that all rounds for such rifles should use blunt-headed shapes and soft alloys. Hornady makes a plastic-capped pointy round that's supposed to be safe, but most opinions seem to be that the added ballistic performance isn't worth the cost of the ammunition - lever-action rifles aren't really made for long-range fire, so the blunt ballistics make no real difference at ranges for which such guns are normally used.  Acroterion   (talk)   18:10, 11 November 2017 (UTC)
 * Cartridges that are detonated by pressure to their rim such as common .22 caliber (0.22 in = 5.6 mm) varieties are safer under pressure to their rear center from another cartridge tip in a tube magazine than Centerfire ammunition would be. Blooteuth (talk) 00:09, 12 November 2017 (UTC)
 * Rifle primers are designed to allow for light strike. For example, an M16 rifle has a free floating firing pin.  When the bolt is retracted and closed as part of the cycle, the firing pin can strike the rifle primer and spec for the primer must allow for a light strike.  The hammer spring must be sufficiently strong to project the firing pin into the primer.  Pistol primers, however, are much more sensitive.  Firing pins for pistols have many more safeguards to prevent any strike. --DHeyward (talk) 06:24, 12 November 2017 (UTC)
 * Primers are constructed for a specific, fast and powerfull impact of a Firing pin with a distinctive shape made out of high-alloy steel to ignite. See here a video about some Gentlemen trying hard to ignite Primers with pointy bullets in a tube. --Kharon (talk) 06:38, 12 November 2017 (UTC)
 * Tube magazines were quite common on early military repeaters as well, such as the Jarmann M1884, the Mauser 1871/84, the Krag–Petersson, the Kropatschek, the Murata Model 22, the Lebel Model 1886, the various Vetterli, and so on and so forth. While quite a few of those used blunt or rounded bullets and/or rimfire ammunition, some used spitzer bullets and centerfire ammunition with no major issues. WegianWarrior (talk) 07:02, 12 November 2017 (UTC)
 * Also see these three videos on YouTube. WegianWarrior (talk) 15:55, 12 November 2017 (UTC)