Wikipedia:Reference desk/Archives/Science/2021 October 7

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October 7

What is the pH of bad motel soap?

The kind that is a poor lubricant cause it's so alkaline it starts irritating after a few continuous minutes and hurts before an hour or so. Sagittarian Milky Way (talk) 02:32, 7 October 2021 (UTC)

I've never had that problem. Have you talked to a skin doctor about this? ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:21, 7 October 2021 (UTC)

Did you ever get a silt-textured piece that's more alkaline than most soap sold in the first world? Sagittarian Milky Way (talk) 04:12, 7 October 2021 (UTC)

I don't know how I would be able to tell the chemical consistency of soap. But if a soap appears to be causing you skin problems, you should see your doctor. ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:25, 7 October 2021 (UTC)

Common supermarket soap isn't as bad. Sagittarian Milky Way (talk) 23:13, 7 October 2021 (UTC)

Then your best bet could be to take your own soap on trips that involve hotel stays. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:43, 7 October 2021 (UTC)

I'll probably regret asking this, but why would you be in contact with soap for "an hour or so"? --Trovatore (talk) 23:44, 7 October 2021 (UTC)

Maybe the OP just likes to be squeaky clean. ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:04, 8 October 2021 (UTC)

The pH of the soap per se is not really meaningful as far as I know, but there are inexpensive universal indicator strips that you could carry around to test the pH of a concentrated aqueous suspension of the soap, such as you would find on the wet bar, if you ever happen to come across it again. --Trovatore (talk) 06:31, 7 October 2021 (UTC)

Are you sure it's the soap? I went to London and the water was so hard. It was very slippery and I couldn't rid the icky feeling while there. Imagine Reason (talk) 12:13, 7 October 2021 (UTC)

The slippery feeling is usually from soft water, not hard. Hard water precipitates out the soap so the soapy feeling goes away quickly; soft water doesn't, and you really have to work to get rid of the soap. --Trovatore (talk) 16:31, 7 October 2021 (UTC)

I have likewise experienced that. It makes the water feel "greasy". ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:49, 7 October 2021 (UTC)

The water in New York City is moderately hard in all Manhattan, most of coastal and South Bronx and a few nearby areas and soft everywhere else. The moderately hard area is only 3 million people. Sagittarian Milky Way (talk) 23:13, 7 October 2021 (UTC)

Soap used to alkaline because it was made from animal fat rendered in lye (sodium hydroxide), but I'd be surprised if that still existed post WW2 or so. Yes there are testing strips (maybe swimming pool supply places sell them) that let you measure pH conveniently. You can also use pink (or was it blue) litmus paper and see how quickly it changes color (stronger alkali = faster and stronger change). Or maybe you could mix a bit of soap solution with an acid such as vinegar, and see if it starts fizzing. 2602:24A:DE47:B8E0:1B43:29FD:A863:33CA (talk) 08:56, 8 October 2021 (UTC)

It would not fizz. The fizzing when you add acid to baking soda is not from the acid/base reaction per se, but from the CO2 released from the sodium bicarbonate when it's acidified. Soaps generally do not contain carbonates or bicarbonates to the best of my knowledge, so there is no reason for them to evolve CO2. --Trovatore (talk) 20:20, 8 October 2021 (UTC)

It's still done, if it says sodium tallowate that means sodium cowfattate which they got from reacting beef fat with lye. I've bought soap from Pakistan or something that says tallowate (at a non-ethnic chain supermarket, NYC is awesome), I don't remember if U.S. soap ever still says that or if they always list the sodium fattyacidate(s) present. If it only says sodium stearate maybe it came from petroleum instead of purified beef fat? If they put 1% too much lye (I think the irritating motel soap says made in [third world country] on the wrapper) it'll still be pretty alkaline in concentrated solutions. Some (not all) common U.S. soaps are still alkaline cause they're highly irritating if you frequently use them as a lubricant 4 or 5 times in a row while Barbasol is far better and vegetable oil even better. Sagittarian Milky Way (talk) 14:58, 8 October 2021 (UTC)

I would expect all soaps that are sodium salts of long-chain fatty acids to be at least somewhat alkaline. Sodium hydroxide is a strong base; long-chain fatty acids are weak acids. --Trovatore (talk) 20:25, 8 October 2021 (UTC)

Internet says sodium stearate has a pH of 10-11, if they keep the pH 7-7.5 glycerol (I don't know) that might knock off a few tenths from dilution (I hadn't thought of it that way (weak neutralizing strong) so had assumed the alkalinity was ~all excess lye that had no fat to react with). I briefly chewed Mg(OH)2 antacids twice a day and didn't spit till my mouth filled with Mg(OH)2 saliva (while waiting for dental appointment) and didn't feel an itch or anything. It's only ~0.2mg/30cc soluble so I'm sure I got the full pH 10.5, seems completely benign. But pH 14 apparently feels like instant regret according to a guy who barely survived a lye drinking suicide. So the difference between no effect even to me and nasty stuff is only a few thousand times more OH ions. Sagittarian Milky Way (talk) 23:33, 8 October 2021 (UTC)

@Sagittarian Milky Way: Were you perhaps thinking of carbolic soap, classically red in colour? That's actually acidic, as it contains phenol or cresol. It was widely used at one time as it was a mild antiseptic but it could also be a skin irritant. Mike Turnbull (talk) 13:37, 9 October 2021 (UTC)

I don't think I've used red soap. I wonder why they chose red. I've used orange germ-killing soap for the same purpose, with some modern antiseptic like triclosan (?) and if I remember correctly it's not the harshest soap I ever used but not great as I suspected for something designed to kill cells. They probably picked something that hurts bacterial cells faster than mammalian cells but it seems the antimicrobial substance adds some harshness. Sagittarian Milky Way (talk) 13:59, 9 October 2021 (UTC)

Adam's Apple in Animals (specifically Great Apes)?

Resolved

The article on Adam's Apple is entirely written in regards to Humans, is the extra swelling and/or deeper voice for males (which appears to be cause/effect) present in other animals, particularly in the great apes? The article on Larynx talks about differences between the Human Larynx and that of the great apes, but the differences by gender aren't part of that.Naraht (talk) 15:54, 7 October 2021 (UTC)

Figure 8.9 in the book Sexual Selection and the Origin of Human Mating Systems by Alan F. Dixson shows a relation between sexual dimorphism in the vocal apparatus (larynx, laryngeal sacs, and hyoid), taken over 24 primate genera, and the mating system. In monogamous systems the relation is weak; it is pronounced in multi-male/multi-female systems and strong in polygyny.  --Lambiam 13:14, 8 October 2021 (UTC)

Thanx, an interesting set of research. Now I know that if my wife catches me cheating, I can say that my Adam's apple makes me more likely to do so. :)Naraht (talk) 01:21, 9 October 2021 (UTC)