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October 3

Heating any metal makes it red??

I find a number of Internet sites saying that a metal can become red when it is very hot. How hot to be specific?? I want a lower limit and an upper limit. The same sites also say that metals can become yellow or blue if heated even further. Can anyone reveal exact temperatures?? Georgia guy (talk) 00:08, 3 October 2023 (UTC)[reply]

Hello, Georgia guy. Please read Incandescence. That article says In practice, virtually all solid or liquid substances start to glow around 798 K (525 °C; 977 °F), with a mildly dull red color, whether or not a chemical reaction takes place that produces light as a result of an exothermic process. Cullen328 (talk) 00:15, 3 October 2023 (UTC)[reply]

I bet that repeating Draper's experiment with a range of human subjects will produce a bell-shaped curve for the temperature where the subjects start perceiving a glow, rather than a sharp transition precisely at 977 °F. --Lambiam 07:41, 3 October 2023 (UTC)[reply]

Probably right, but I guess the deviation will be quite small. Basically receptors are mostly identical, which leaves pupil diameter, lense transeparency and receptors prevalence as actual factors. Leave out extreme cases like severe cataract and the resulting variance will be small. Zarnivop (talk) 13:54, 4 October 2023 (UTC)[reply]

Another good read would be black body radiation. --OuroborosCobra (talk) 00:48, 3 October 2023 (UTC)[reply]

Also Pyrognomic, Thermal radiation and Planckian locus. --Lambiam 07:20, 3 October 2023 (UTC)[reply]

No exact temperatures, as the changes from invisible to red to orange are gradual. There are lava lakes that appear grey in daylight but clearly glow red at night. And where is the boundary between red and orange?

All hot, dense materials glow. So of the metals, mercury is out, as it evaporates before being hot enough. In normal gases, the density is so low that interactions between particles are too weak to create continuum emissions.

Most metals have a fairly flat reflectivity over the visible spectrum, so they are close to blackbody emitters. Copper and gold are notable exceptions, which have a high reflectivity (and therefore low emissivity) in red. PiusImpavidus (talk) 07:57, 3 October 2023 (UTC)[reply]

798 K is well below the critical point of mercury (our article says "1750 K, 172.00 MPa"), so presumably if you can keep the pressure high enough you could keep it as a liquid. Calculating using NIST's Antoine equation parameters suggests a minimum of about 11.25 barr. DMacks (talk) 15:04, 3 October 2023 (UTC)[reply]

@Georgia guy: It doesn't have to be metal. Anything at a given temperature emits blackbody radiation, though some materials emit or absorb spectral lines (due to electronic transitions) that overwhelm the blackbody radiation. Though the peak wavelength depends on temperature, other wavelengths including red are emitted, as in this graph or this visualisation. Whether our eyes interpret it as red depends on various psychological and psychological effects. As other respondents have replied, the boundaries are inexact and depend on observer, material and viewing conditions. Cheers, cmɢʟee⎆τaʟκ 12:17, 3 October 2023 (UTC)[reply]

You might also want to look at this particular chromaticity diagram that include color temperatures: https://www.luxalight.eu/sites/default/files/inline-images/CIE_ledtuning_1.jpg Dhrm77 (talk) 14:50, 4 October 2023 (UTC)[reply]

I think there may be a misunderstanding here between the actual glow of "red-hot" metals (that is essentially caused by blackbody radiation), and the thermal discolourations ("heat tint") that happens to stainless steels. As I understand it, these permanent discolourations are mostly due to small layers of nickel oxides building up on shiny surfaces. These are very different processes. --Stephan Schulz (talk) 20:37, 5 October 2023 (UTC)[reply]

Why do car wheels have an odd number of spokes?

Wheels (besides bicycle ones with thin tensioned ones) often have five spokes (or ten, comprising five pairs). Some I've seen have three.

https://engineering.stackexchange.com/a/14606 claims it's "because having directly opposed spokes causes problems with residual stress distribution as the casting cools and shrink". Is that true? If so, why do having opposed spokes have this issue. What other reasons might there be?

Thanks,
cmɢʟee⎆τaʟκ 12:28, 3 October 2023 (UTC)[reply]

In 5 spoke wheels, any one spoke has two directly opposing spokes that will reduce the effect of torsional vibration. With 6 or 8 spokes, there is a directly opposing spoke that creates a henge point. This henge point leads torsional vibration around the two opposing spokes. In addition, having an even number of directly opposing spokes causes problems with the residual stress distribution of the wheel as it cools and shrinks. This is highly evident in cast iron handwheels having "S" shaped spokes. With an even number of spokes, you have a directly opposing spoke that creates a henge point, so you can get torsional vibration around the two opposing spokes. [1]

However, the exact definition of "henge point" eludes me at present, but I'm sure one of the sages here will be able to enlighten us. Alansplodge (talk) 13:59, 3 October 2023 (UTC)[reply]

A typo for 'hinge point', surely? AndyTheGrump (talk) 14:03, 3 October 2023 (UTC)[reply]

I'd agree to some extent about the cooling issue, the torsional one sounds like at best one bizarre pre FEA case that got generalised. I was design engineer on a 5 spoke and a 3 spoke. https://www.carsguide.com.au/car-reviews/used-car-review-ford-falcon-eb-1991-1993-13217 and https://bringatrailer.com/2017/06/03/little-red-orphan-1993-mercury-capri-xr2-turbo-5-speed/ Greglocock (talk) 22:47, 3 October 2023 (UTC)[reply]

According to this source, wheels with 3 and 4 spokes didn't sell well, people preferred 5 spokes. So the reason could simply be esthetics. Prevalence 14:08, 3 October 2023 (UTC)[reply]

Internal stress in a solid object such as a car wheel is greatest with a possibility of breakage when road vibrations match a Mechanical resonance of the wheel. Therefore a wheel designer is concerned about the Normal modes of vibration in which all parts of the wheel move sinusoidally with the same frequency and with a fixed phase relation. Ernst Chladni invented a technique to show Chladni figures which are nodal lines that divide parts of a plate that resonate in opposite directions. This lead to the study of Cymatics of objects of various shapes. The Chladni figure of a car wheel that has an even number of spokes is dominated by a full diameter nodal line that indicates a fundamental vibration mode that could lead to catastrophic breakage and is therefore avoided. Philvoids (talk) 15:52, 3 October 2023 (UTC)[reply]

Interesting theory, but in that case disc like (unspoked) wheels would break, whereas in fact they are the strongest. Greglocock (talk) 22:49, 3 October 2023 (UTC)[reply]

It may be spoked that a one-spoke disc is odd. Philvoids (talk) 09:54, 4 October 2023 (UTC)[reply]

Perhaps the vibrations would be dissapated throughout the disc, rather than being channelled along an individual spoke? Alansplodge (talk) 12:12, 4 October 2023 (UTC)[reply]

Who appointed you spokesman? —Tamfang (talk) 17:18, 4 October 2023 (UTC)[reply]

I didn't realise there was an appointment process. Alansplodge (talk) 12:20, 5 October 2023 (UTC)[reply]

I hereby anoint thee the odd-spokesperson. Clarityfiend (talk) 01:12, 6 October 2023 (UTC)[reply]

What is the origin of the phrase "putting a spoke in" someone's wheel? I understand it to mean obstructing their efforts, but from this discussion it should mean making them go more smoothly. 89.243.13.60 (talk) 10:58, 6 October 2023 (UTC)[reply]

Apparently "based on the use of the word 'spoke' in the sense of a bar used to prevent the wheel of a vehicle from turning, especially when going down hill". [2] Alansplodge (talk) 18:11, 6 October 2023 (UTC)[reply]

(Continuing OT) also known as a "scotch". Historically, and on heritage lines, used to stop parked railway wagons moving if they didn't have a functional handbrake. Martin of Sheffield (talk) 09:25, 7 October 2023 (UTC)[reply]

Thanks a lot, everyone. Learnt quite a bit here. cmɢʟee⎆τaʟκ 07:21, 7 October 2023 (UTC)[reply]

I question the premise of this question. When I Google "six spoked auto wheels", I find many results, and it seems that many businesses are making money as we speak selling six spoked wheels. Cullen328 (talk) 07:34, 7 October 2023 (UTC)[reply]

They have scotch'd the snake, not killed it. What does that phrase actually mean? 2A00:23C3:9900:9401:4979:A935:6AAD:7D60 (talk) 10:50, 7 October 2023 (UTC)[reply]

Wiktionary:scotch#Verb 1. "to wound superficially". For Martin's point above, see 4. "To block a wheel or other round object". Alansplodge (talk) 10:27, 8 October 2023 (UTC)[reply]

Scotch, vt, 2a "To render (something dangerous or undesirable) temporarily harmless or less harmful, without destroying it completely.""scotch". Oxford English Dictionary (Online ed.). Oxford University Press. doi:10.1093/OED/5372422318. (Subscription or participating institution membership required.) Originally (in Shakespeare's time) the word used was "scorch'd" but later editions substitutes "scotch'd" but apparently modern scholars are reverting to scorch (vt, def 3) itself a variant of to score. Thus the meaning is that the snake is wounded and not killed. As regards the railway use, a scotch is something (typically a wedge-shaped block) placed under a wheel (again see OED), but with railway wagons there are usually holes in the wheel disks and a bar can be placed through them which is more secure. See Armagh rail disaster for why putting a stone under the wheel is not a good idea. Martin of Sheffield (talk) 14:33, 8 October 2023 (UTC)[reply]

When did recycling start in your countries?

In the U.S., I heard someone say that recycling started after the Environmental Quality Improvement Act of 1970, signed by President Nixon. But in Illinois and California, the garbage truck takes black or green garbage bins, and the recycling is a blue bin. But as a kid in the 1990s, I never saw the blue bins, but I see it now. So I think recycling came much later than 1970, but maybe it depends on jurisdiction? 170.76.231.162 (talk) 16:00, 3 October 2023 (UTC).[reply]

Recognizably-colored bins are probably a much later innovation, as are having separate bins out in public places (or for pickup adjacent to trash). When I worked a community recycling project around 1990, the local government dropped off a few regular dumpsters at some mass-transit parking lots on Saturdays, with informal signs "paper", "clear glass", "steel", etc. and I vaguely recall a regular compactor trash-truck that we used for plastic bottles. Residents could drive in and drop off their household materials--most were either loose in their trunks or in whatever box/bin/bag they happened to have at their house. I have no idea what the county did with those dumpsters-full of each type of material. But weekly curbside pickup was solely headed to the landfill, as were the only bins anywhere in public. DMacks (talk) 16:12, 3 October 2023 (UTC)[reply]

In the UK, charities used to collect old newspapers for recycling in the 1970s and 1980s. The reward was IIRC, about £20 per Imperial ton, which was pretty much a roomful. In the 1990s aluminium drinks cans were also collected. which required less space (but more wasps). Both income streams were lost when local councils began recycling.

This article dates local authority recycling in the UK to the Environmental Protection Act 1990 and in the US to a similar timeframe, with a few cities leading the way in the late 1980s according to this source. Alansplodge (talk) 16:31, 3 October 2023 (UTC)[reply]

Another form of newspaper recycling was done by fish-and-chip shops, which at that date used newspapers for the outer wrappings. If you were known to the chippy and trusted that the papers would be in clean condition, you could trade a couple of week's broadsheets for a bag of chips and batter scraps. Great for the walk home from the pub. Martin of Sheffield (talk) 16:38, 3 October 2023 (UTC)[reply]

There were a series of recycling (then called "salvage") campaigns in Britain during the Second World War, perhaps the best known being the collection of aluminium pots and pans, which housewives were assured would be turned into Spitfires. Another less productive effort was the collection of Victorian iron railings which adorned the front gardens of many urban houses; the iron recovered was of such poor quality that heaps of railings remained at steel works until the 1970s, others were used as ballast in ships or [allegedly] just dumped in the sea. [3] [4] Alansplodge (talk) 16:47, 3 October 2023 (UTC)[reply]

Not just houses, also businesses and churches. Martin of Sheffield (talk) 16:56, 3 October 2023 (UTC)[reply]

I remember collecting the aluminium foil tops from glass milk bottles, in the late 60s/early 70s. I have a vague thought that they were given to a charity which could sell them, presumably for recycling? -- Verbarson ^talk_edits 18:10, 3 October 2023 (UTC)[reply]

Those went to the "Blind Dogs for the Blind" charity. Curiously, they were only interested in the milk-bottle tops, not other aluminium foil. Were the tops of a special alloy or particularly pure aliminium? JMCHutchinson (talk) 12:04, 5 October 2023 (UTC)[reply]

Possibly the volume and ubiquity of bottle-tops made them ideal targets, as everyone had milk bottles delivered daily (and we had free milk at school in 1⁄3-pint bottles). In those days, I'd never heard of metal trays for take-aways. I do remember flattening the tops and threading them onto long pieces of string. -- Verbarson ^talk_edits 14:46, 5 October 2023 (UTC)[reply]

In America, "paper drives" were a thing at least as far back as World War I. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:35, 3 October 2023 (UTC)[reply]

See also History of bottle recycling in the United States. And I remember wrapping piles of newspaper in twine & taking them to be recycled on Long Island circa 1970. Pretty sure there we also brought in aluminum cans. - Jmabel | Talk 04:02, 4 October 2023 (UTC)[reply]

For what it's worth... when I moved into a house here in Toronto, Canada, in 1983, garbage was collected twice a week. Then in 1988 every household was given a blue box to be used to recycle glass and plastic bottles; they changed one of the garbage collections to a blue-box collection. Recycling of other materials followed over the next few years and has continued to expand, now using wheelie-bins instead of open boxes. The original poster said "in your country", but here this stuff is all organized at the municipal level. --142.112.221.246 (talk) 06:52, 4 October 2023 (UTC)[reply]

When recycling became popular there was reference in the literature to "the local authority salvage schemes of the seventies." In Oxford there was a monthly collection of bundles of old newspapers on a day different from the regular weekly refuse collection. The government has claimed that it cannot reverse the repeal of the statutory requirement that local authorities collect refuse no less often than once a week. Mid-Suffolk has taken advantage of that with its "twin bin" system. Residents have two bins - a black bin and a green bin. So if the collection day is Tuesday they put out the black bin (refuse) one week and the green bin (recycling) the next. From time to time the council pushes colour coded calendars through letterboxes explaining when the collection days are. There used to be a deposit on glass bottles, which could be redeemed on returning them to the shop (which naturally included any stray bottles which might be picked up). The milkman used to place milk in glass bottles on doorsteps at 5 AM, collecting the empties for washing and reuse at the same time. 80.43.75.165 (talk) 10:28, 4 October 2023 (UTC)[reply]

Zabbaleen: Around the 1910s, a group of Muslim migrants from the Dakhla oasis in the Western desert of Egypt relocated to Cairo in an area known as Bab El Bahr, which is situated between Attaba and Ramses square in downtown Cairo.[2][17][18][19] These people are known as the Wahiya (singular: wahi), which means people of the oasis.[18][19] The Wahiya assumed the sole responsibility for the collection and disposal of Cairo's household waste under the framework of contracts with building owners in Cairo. In this system, the Wahiya paid the owners of buildings an initial sum and then collected monthly fees from the tenants for their services.[17][18][20]

--Error (talk) 15:11, 4 October 2023 (UTC)[reply]

Glass has been recycled since antiquity. Collecting broken glass was much cheaper than ordering new glass from Phoenicia, or Venice, in particular when those who knew how to make it wanted to keep their monopoly. But there have been times, like in the 20th century, when industrial production of glass was so cheap and manual collection of old glass so expensive that it was simply thrown away, until people slowly started to realise (and this process isn't complete yet) that Mother Nature doesn't freely handle all our waste. My mother told me that around 1960 here in the Netherlands (or at least, in her town) glass was simply thrown in the wastebin, but I remember that by the late 1980s you could throw it in three containers (white, green, brown) near a local store (literally throw; when the glass breaks, more fits in the container).

Fibres have been recycled for ages too. Paper was recycled, old clothes turned into paper, and today (at least experimentally) old clothes can be broken down to fibres, made into new threads and finally new clothes.

Metals can generally be separated from other waste magnetically, either directly or from the ashes after incineration. So metals could be recycled well before they were collected separately. The main reason to keep metals separate from non-recyclable waste is to be able to charge more for the latter. IIRC, plastics recycling from household waste started in the mid-2000s, drinking cartons were added in the early 2010s. We now put plastic, drinking cartons and metals all in the same bin; those are separated later. In other municipalities those are put in one bin together with non-recyclable waste, or even compostable waste, and are separated later. Generally, the larger the city, the less well people keep their waste separated.

Note: recycling is different from reusing. If a glass bottle is undamaged, it can be reused. I wrote above about recycling stuff that can't be reused. PiusImpavidus (talk) 20:11, 4 October 2023 (UTC)[reply]

Just ten minutes ago I watched the contents of my new, council issued FOGO bin collected for the very first time here in a suburb of Melbourne, Australia. FOGO stands for Food Organics Garden Organics, and means that both garden and kitchen waste are now collected and processed together to create compost that can be used to improve soils for food production. But I can recall collecting glass bottles, newspapers and metals as a child 60 to 70 years ago for some remuneration. The difference now is that we pay the council to do it! HiLo48 (talk) 02:52, 5 October 2023 (UTC)[reply]

As children in Cornwall in the 70s we saved milk bottle tops for guide dogs and lifeboats and the like. If we were lucky we would find empty Corona pop bottles (dropped by stupid emmets), which we could get 5p or 10p for (they had to have the lid) at the local shop. Leftovers from school dinners went to pig slop - watching the slop trays to make sure nobody put anything they shouldn't into them was a trusted and coveted position amongst primary school children. Coal came in cloth sacks that were reused by the merchant. DuncanHill (talk) 11:22, 6 October 2023 (UTC)[reply]

An oddity I've just noticed. I've had a nasty cold and associated cough which is hanging on a bit. I've just opened a bottle of cough medicine which is based upon Guaifenesin and I notice that the glass bottle has "Don't Recycle" on it. I can't see the sense myself, glass is recycled by remelting at temperatures over 1,000°C so I'd hardly think any organics or liquids would be present. Presumably it's meant to go to landfill where it can leach out? Martin of Sheffield (talk) 15:29, 8 October 2023 (UTC)[reply]

@Martin of Sheffield: Is the bottle a non-standard design for a proprietor protecting their exclusive product image i.e. "Don't recycle" really means "Don't refill or resale"? With best wishes for your speedy recovery Martin. Philvoids (talk) 16:15, 8 October 2023 (UTC)[reply]

Not as far as I can tell, standard 300ml brown glass with a child-resistant cap from Aldi. Thanks for the good wishes Martin of Sheffield (talk) 16:21, 8 October 2023 (UTC)[reply]