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March 3

Aqueous AlCl3

What's the Ka or pKa of AlCl₃ in water? (Not homework -- I need to make sure I'm mixing my chemicals right, but I can't find a reliable value for this parameter anywhere!) 2601:646:9882:46E0:A9DB:D35F:F7B8:E80B (talk) 06:13, 3 March 2023 (UTC)[reply]

The acid in this reaction is the hexahyrdate aluminum complex ion, Al(H₂O)₆³⁺. According to This, the Ka of this ion is 1.4 x 10^-5. --Jayron 32 11:53, 3 March 2023 (UTC)[reply]

Thanks! 2601:646:9882:46E0:780E:6C08:3DB3:8473 (talk) 05:29, 4 March 2023 (UTC)[reply]

Wristwatch gears

Wristwatches have tiny gears which have been made for more than a hundred years. How have these gears been made so accurately? If they are stamped, how is the master punch made? 24.72.82.173 (talk) 17:36, 3 March 2023 (UTC)[reply]

Does This help you with your research? --Jayron 32 18:13, 3 March 2023 (UTC)[reply]

Here is a manual demonstration; the commentary suggests that high-quality commercial gears are made by CNC machines rather than stamped out. -- Verbarson ^talk_edits 23:35, 3 March 2023 (UTC)[reply]

These were, however, not available in the 19th century, so the question remains which techniques were employed by 19th-century watchmakers. --Lambiam 14:59, 4 March 2023 (UTC)[reply]

One of the sources in the article Watchmaker is this interesting book Practical Watchmaking, first published 1788. Chapter IV, "The Wheels", has a subheading "The Teeth", which says:

To split wheels one uses the tool, Pl. 12, Fig. 1. See its description in the Vocabulary, the article on wheel cutting machines.

In the Vocabulary under Wheel cutting machine there is this description:

It is composed of a frame in the shape of triangle, in which the arbor A is so skilfully adjusted that it turns exactly and free in this type of frame. It carries a bass plate called the dividing plate (plate-forme), which is fixed immovably to the base of the arbor so that these two parts turn in unison. Surface B of the dividing plate has several divided and numbered concentric circles of different numbers, in order to give a wheel the number of teeth which it needs. The part K, called the alidade, is a steel arm which springs. One end is fixed at the point N, on one of the pillars of the frame. It carries a pointed screw L, which enters the divisions of the dividing plate and holds it fixed at this point. The carriage F slides on the arm O of the frame, on which the carriage can come and go by means of a screw which moves it towards or away from the arbor A, according to the size of the wheel. Fixed on the carriage is a hinge Q, which holds a toothed wheel, mounted on an arbor, on the end of which the crank I is placed. This wheel meshes with a pinion P which carries a steel wheel cut in the shape of file, called a fraise or cutter. So when the crank I is turned, the wheel turns the cutter R. Let us suppose that you want to split a wheel. Enlarge the hole until it enters the pivot of the screw H and fix it there with the nut M. Then place the alidade on the line of the plate No . 60. Approach the carriage of the wheel little by little, to be sure that the teeth of the wheel will be neither too long nor too short. Then fix the carriage by means of the lock screw E, and turn the crank while pressing the hinge Q lightly against the wheel. The cutter, by filing the wheel, will split a tooth. That one split, change the alidade point to split another, and continue until you have made a full turn of the dividing plate.

I hope you can picture that clearly in your mind. :) Obviously it goes along with the illustration plate 12, where we can see that this device looks somewhat like a record turntable. I'm not certain how big it is in relation to the toothed wheel being created. I wonder if it has some aspect of a pantograph for the purpose of scaling down a design? (The arm is suggestive of that.) It's evidently a species of lathe, and the thing which always impressed me about lathes is that the parts for lathes are made using other lathes: thus they went through a kind of evolutionary or bootstrapping process.

I also did an image search and found a series of pictures titled Rare and antique Watchmaker Milling Machine with wheel cutting attachment. I don't know how antique is "antique" but it gives you a general idea of the shape and size of this kind of machine. I imagine it descends from a series of cruder ancestors, starting with one that made the gears for clocks (and for the next, slightly more accurate wheel cutting machine). Card Zero (talk) 16:23, 4 March 2023 (UTC)[reply]

Thanks for taking the time to reply. Unfortunately, I couldn't clearly (in fact not even nebulously!) picture the device in my mind. The gears I saw on the TV program "How Do They Do It?" were about 2 mm in diameter, which seems smaller than what the machine in the videos would be capable of. 24.72.82.173 (talk) 19:44, 4 March 2023 (UTC)[reply]

What time is it on the Moon?

Is this something that belongs in the Moon or in another one?— Vchimpanzee • talk • contributions • 22:53, 3 March 2023 (UTC)[reply]

Has anything actually happened yet? ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:12, 3 March 2023 (UTC)[reply]

I guess it's too early, but certainly the proposal needs to have a brief mention at some point.— Vchimpanzee • talk • contributions • 23:21, 3 March 2023 (UTC)[reply]

They could use local time until the infrastructure is set up, see Railway time. Martin of Sheffield (talk) 08:31, 4 March 2023 (UTC)[reply]

19th Century railways initially lacked a seconds-accurate clock distribution but everyone was sure about their longitude, and therefore which time zone they occupied. 21st Century Moon-walkers will have near-instant data communications but the Moon's Earth-referenced Earth-fixed longitude, and therefore which Earth time zone might be relevant, keeps varying. A good solution to timekeeping on 19th century railways therefore doesn't address the issue of Moon timekeeping.

A possible solution is to adopt Earth GPS (Global Positioning System) time for the whole Moon. Sensitive GPS receivers may be able to provide surface locations on the Moon, necessarily for Earth-facing fixed locations using long integration times and Kalman filtering, because the GPS satellites (4 are needed for a trilateral location fix) were designed to transmit to Earth with only incidental stray radiation towards the Moon. The concept is credible enough for tests planned by a NASA Lunar GNSS Receiver Experiment (LuGRE) in 2023 and by ESA in 2024. Given a lock on GPS time that can certainly be distributed all over the Moon using local radio clocks, I think any subdivision into local time zones would be as premature as are plans for Colonization of the Moon. Philvoids (talk) 13:10, 4 March 2023 (UTC)[reply]

My question was where to put this information on Wikipedia.— Vchimpanzee • talk • contributions • 16:15, 4 March 2023 (UTC)[reply]

Until or unless they come up with a solid plan that has a reasonable chance of approval, the answer is "nowhere". One thing to keep in mind is that a "day" on the moon is about a month on earth. ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:04, 4 March 2023 (UTC)[reply]

Perhaps European Space Agency as it seems to be their baby. Curious that they have nothing more urgent to discuss. Alansplodge (talk) 21:02, 4 March 2023 (UTC)[reply]

Urgent? I first raised this issue in 2005. -- Jack of Oz ^{[pleasantries]} 21:43, 4 March 2023 (UTC)[reply]

It probably won't be a thing until or if we start forming permanent settlements on the moon. And maybe not even then. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:02, 4 March 2023 (UTC)[reply]

The Apollo 11 article timings are all given in UTC. This was presumably UTC as recorded by the ground station, so about 1.25 seconds behind Moon time? -- Verbarson ^talk_edits 23:29, 4 March 2023 (UTC)[reply]

I expect that the JWST scientists have figured out a way to sync the clocks here and there, possibly with microsecond accuracy, in spite of the communication delay (about 5 seconds). It may not be exactly rocket science to get this working. --Lambiam 09:52, 5 March 2023 (UTC)[reply]

Plain old-fashioned ntp (or it's offspring chrony) would do that. It is specifically designed to allow for delays between the primary source and the local clock. Martin of Sheffield (talk) 11:13, 5 March 2023 (UTC)[reply]

Because the gravitational potential on the moon is less than on Earth, clock will run faster there. So if you try to sync from Earth, it will try to keep slowing down the faster clock on the moon. With microsecond accuracy this will be noticed. So do you want to say a second is longer on the moon, or allow clocks to drift apart? There is a system for the solar system called Barycentric Coordinate Time. Graeme Bartlett (talk) 23:57, 7 March 2023 (UTC)[reply]

I'm not sure why this is in the news (also here), but the problem itself is old news. What seems to be new is framing the issue in terms of a lunar "time zone", but that is IMO a red herring. I think the material deserves mention in a section of the article Satellite navigation. --Lambiam 16:45, 11 March 2023 (UTC)[reply]