Science desk
< March 1	<< Feb \| March \| Apr >>	March 3 >

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.

March 2

Chemical grades

What's the difference between "lab grade" and "reagent grade" cupric oxide in terms of impurities (and especially iron content)? Also, for ACS grade phosphoric acid, what's the maximum allowable iron content? 2601:646:8E01:7E0B:0:0:0:64DA (talk) 06:10, 2 March 2018 (UTC)[reply]

Reagent grade will mean it meets the standard of "Committee on Analytical Reagents of the American Chemical Society". Perhaps 95% pure. Lab grade is not so good, and you had better check the manufacturer specs. ACS grade is likely the same as reagent grade. Graeme Bartlett (talk) 10:06, 2 March 2018 (UTC)[reply]

ACS grade phosphoric acid allows up to 30 ppm of iron in phosphoric acid. So if you want 1 part per million this is not the standard you need. The reference is ISBN 9780841230460. ACS grade cupric oxide can contain up to 500 ppm of iron. Graeme Bartlett (talk) 11:22, 2 March 2018 (UTC)[reply]

These phphoric acid products have less than 10 ppm iron[1][2]. This one is extremely pure: [3], but you will pay heavily. Graeme Bartlett (talk) 11:40, 2 March 2018 (UTC)[reply]

500 ppm of iron in the copper oxide?! Mother of God! Are there any higher grades of the stuff??? (Incidentally, the acid is less of a problem, because I now know a few tricks for purifying it.) Also, how about the standards for copper carbonate and copper hydroxide (my Plan B if I can't get copper oxide of decent quality)? 2601:646:8E01:7E0B:59E2:B6:A6B8:FAC7 (talk) 09:43, 3 March 2018 (UTC)[reply]

These two do not have a reagent standard from ACS. The list of what there are standards for is available here: https://pubs.acs.org/isbn/9780841230460 Graeme Bartlett (talk) 11:02, 3 March 2018 (UTC)[reply]

Is there a health advantage in skimming cooked watery food?

I'm not sure how common it is in nowadays world widely but I'm sure that it's most common in Arabic countries to skim foods while cooking, it says to remove the "scum" from the surface of these dishes while cooking. (That is the definition that I found for "skim" on the internet: "To remove scum, fat or other impurities from the surface of a liquid, such as stock or jam, while it is cooking."). It's mainly common in meat dishes but not only, it's commonly used also also for fabaceae. Now my question is if there is/ are health advantage/s / beneficials for this act? The rumors claim that this "scum" of the surface is not healthy to the body. Furthermore I read in the past that there are in the "scum" some proteins that the body doesn't like 93.126.116.89 (talk) 18:04, 2 March 2018 (UTC)[reply]

Fabacaea is a fancy way of saying “legumes.”Edison (talk) 18:19, 2 March 2018 (UTC)[reply]

Legumes is a fancy way of saying "beans". --Jayron 32 18:44, 2 March 2018 (UTC)[reply]

"Beans" is a fancy way of saying testicles? What is the source of this "Arabic countries" claim? My dad is not Arabic, and he boils a lot of his meats and discards the fat. It makes his chili taste like dry dog food (yes, I have eaten dog food, although it's been decades, and was for fun), and you have to add fat (olive oil or sour cream) to make it edible. μηδείς (talk) 19:27, 2 March 2018 (UTC)[reply]

The source for "Arabic countries" is likely the OP. I.E. they are going by their own personal experience and knowledge. It's true that this isn't a good source, but it's also largely irrelevant. The only reason they appear to have brought this up is to explain the background as to why they have this question. Even if it isn't as common in Arabic countries as suggested, the question itself is still valid. Nil Einne (talk) 13:37, 3 March 2018 (UTC)[reply]

This seems to be an WP:ENGVAR issue. A peanut is a legume. I would not call it a bean. In fact, I would not even call many peas beans. Our Bean article also talks about the complexity of defining what a bean is. Nil Einne (talk) 13:43, 3 March 2018 (UTC)[reply]

This seems to be a Poe's law issue; jokes aren't funny when you have to explain them. We'll just go back to pretending you have a sense of humor. It was better that way. --Jayron 32 00:18, 5 March 2018 (UTC)[reply]

I think this comes up in western cooking frequently when talking about making stock. Here, the consensus is that skimming the foam off simmering stock is for reasons of aesthetics and taste rather than health. - Nunh-huh 19:37, 2 March 2018 (UTC)[reply]

Indeed I'm not a native English speaker and by fabacaea I meant to any kind of legumes (such as beans, peas, chick-pea, lentils etc.). I'm afraid that my question regarding to the health advantages of skimming will become a conversion about the definition of fabacaeae. If it complicates my question, then you can remove the part which talks about fabaceae and refer the rest:) Thank you! 93.126.116.89 (talk) 19:41, 2 March 2018 (UTC)[reply]

Burn Rates

I'm trying to find a table of average Burn rates for materials which might or might not be considered explosive. Burn rates should be specified by comparative numbers, not ordinals; for example, meters/second (or fps). I would like common substances, such as:

Substance	Burn Rate (m/s)
Cigarette embers	0.5 - 3.0
Kitchen match	40 - 110
Campfire	200 - 300
Fireworks	450 - 1500
Black powder	1100 - 2000
TNT	7500 - 9000

All the burn rates in the above table are made up; that's what I need.

I don't need a table. A long discussion (or many articles) of various materials that has the numeric burn rates embedded in the paragraph(s) will do just fine. And I know that burn rates are subject to discussion. What I want is an average range that covers 75 to 90 percent of the possible values.

Anything you can provide me will be greatly appreciated.

--RoyGoldsmith (talk) 21:08, 2 March 2018 (UTC)[reply]

No idea about low-velocity stuff like cigarettes but this stuff is measured carefully for rocket propellants (see articles related to specific impulse). I click around a little and couldn't find any tabulation, which surprised me. But fancy rockets use difficult-to-handle cryogenic liquid hydrogen and LOX because of its high velocity (resulting from low molecular weight). People even tried to use the even nastier hydrogen fluoride but that luckily was considered unmanageable. 173.228.123.121 (talk) 01:50, 3 March 2018 (UTC)[reply]

Look for a publication of the Lawrence Livermore National Laboratory Properties of Chemical Explosives[4] which has detonation velocity for many compounds. They use mm/μsecond (which is km/sec) Graeme Bartlett (talk) 04:33, 3 March 2018 (UTC)[reply]

Considering how long a cigarette lasts, a better estimate would be 0.5 m/h 78.0.254.206 (talk) 05:43, 3 March 2018 (UTC)[reply]

Note that the OP is asking about cigarette embers, not cigarettes. Nil Einne (talk) 15:13, 3 March 2018 (UTC)[reply]

Note that the OP explicitly states that the numbers are made up. A campfire that burned at 300 m/s would be quite a sight. μηδείς (talk) 19:15, 3 March 2018 (UTC)[reply]

Yes but I think we all know the numbers are made up. That's the point. (Okay 'estimate' sort of implies more work went into it then likely did but still, that seems to be about the IP's number as much as anything. And I admit, I should have said, 'the OP mentioned' rather than 'the OP is asking about'.) Nil Einne (talk) 10:45, 4 March 2018 (UTC)[reply]

I really don't need a table or cigarettes at all. I just want to come up with a range of burn rates that distinguish between explosives and simple burning. Like "Anything with a burn rate of [and I'm making this up] 200 m/s or below (like a campfire) is not an explosive; anything with a burn rate of 700 or above (like fireworks) is an explosive. Anything within the range of 200 to 700 (a sparkler?), the decision must be made based on the individual material in question."

I realize that explosives are not judged solely on burn rates and I know that, if you get down in the weeds, there are always exceptions (sap exploding in a campfire). If someone knows something better than burn rates to distinguish what is and is not an explosive, please tell me what is it? (For example, it could be based on hearing: if it roars, it's a fire; if it bangs, it's an explosion.) What I want is a general answer, understandable to high school students when I talk to them about explosives. --RoyGoldsmith (talk) 23:58, 4 March 2018 (UTC)[reply]

I've always thought that explosives contain their own embedded oxidant, while slower forms of burning depend on oxygen from the surrounding atmosphere. Not sure if this leads to a correct definition of explosives. Our article on explosives says "the distinction, however, is not razor-sharp" (about the distinction between explosive and combustible substances). Jahoe (talk) 11:32, 5 March 2018 (UTC)[reply]

I am not aware of a scientifically-accurate definition of an "explosive". The usual argument^{[citation needed]} is that it is an explosion if the reaction rate varies "a lot" and the reaction accelerates until it runs out of fuel, whereas a flame (e.g. a bonfire) consumes the material at a more or less constant rate; but that hinges on your appreciation of whether the rate is accelerating "a lot".

In the sound-based criterion, the "bang" will come from the difference between detonation vs. deflagration, which is scientifically significant (the physics are completely different depending on which side of the sound speed you are on), and give the classification between high and low explosives. Tigraan^{Click here to contact me} 18:39, 5 March 2018 (UTC)[reply]

OK. But check me. Low explosives (propane, gasoline, black and smokeless gunpowder, flares, fireworks) burn when unrestrained by a container. They only explode (with a supersonic BANG) when surrounded by something (cardboard? paper? a gas tank?) that causes an instantaneous (or longer) increase in the inclosing pressure. A low explosive not under pressure can, in a sense, be considered not an explosive at all; it just burns, possibly at a very high rate and temperature. A high explosive detonates whether surrounded by something or not because the material itself is dense enough to contain a shockwave propagating at supersonic velocities.

Have I got it right? Explosives (high school, non-science definition) are substances that ignite with a faster-than-sound bang. --RoyGoldsmith (talk) 23:54, 6 March 2018 (UTC)[reply]

@RoyGoldsmith: You are roughly correct, though as hinted by the {{cn}} I placed on my own claim, there might be... somewhere... a definition of "explosive" that makes it wrong. Now, since I have a nitpicker-in-chief reputation to defend:

Detonation is always an environment-dependent process since the various speeds involved change with temperature/pressure etc., the "high explosive" class refers to standard outdoors conditions. For instance, gasoline under atmospheric temperature/pressure is quite hard to ignite ("cars just don't explode"), but if you try to push an old engine to its limits you may cause engine knocking which is a form of detonation (but inside an engine, air is heated by compression).
It is not (or rather, not only) being dense that causes the transition to detonation. It is also because of a high energy density.

Tigraan^{Click here to contact me} 20:00, 8 March 2018 (UTC)[reply]

@Tigraan: On your points:

And the knock is perceived as a rap, not a bang. It's only when the listener is close enough to hear the shockwave travelling fast than sound that it sounds to him like a bang. Distant explosions only rumble.
I knew that "dense" was not quite the word; "energy-dense" is better. I think it is better to say that my high-school definition is better applied to explosions, rather than explosives.

But here's a thought: By my definition, can there be explosions in a (say for the sake of argument) pure vacuum? Wouldn't the lack of pushback make the leading edge travel at less than the speed of sound? Say we have a man in a spacesuit who observes an explosion a mile away. At first he hears nothing. When the shockwave reaches him, wouldn't he hear a (possibly earsplitting) rumble but not anything he would describe as a bang? As long as there was an inch of vacuum between the spacesuit and the explosive material, wouldn't he not hear a bang?

What I'm saying is that, by my definition, you've got to have a (human) observer in the mix so that he can tell us whether he heard a bang. A legal definition (witnesses and all that) rather than a scientific one (reproducible data).

Or maybe a scientific one too. When you hear the crack of a whip, is the air moving past your ear travelling faster than sound? If so, we can substitute "air moving past your observation point faster than sound" for "a human observer". --RoyGoldsmith (talk)

Well, there is no sound in space/vacuum, and you need matter to transmit soundwaves. Tigraan^{Click here to contact me} 17:28, 9 March 2018 (UTC)[reply]

Neanderthal, rats

Did Neanderthals have rats or mice as pests?144.35.114.28 (talk) 21:36, 2 March 2018 (UTC)[reply]

Word is that house mice Mus musculus arose in the Middle East at the dawn of agriculture, long after the Neanderthals were gone. Rats are older, but one wonders how well they would do as commensals with hunting-gathering ice age Neanderthals. Probably not in any kind of permanent association. As an example, the Canadian province of Alberta is rat-free. Heaviside glow (talk) 22:46, 2 March 2018 (UTC)[reply]

They can survive Norway cold but not Alberta? Sagittarian Milky Way (talk) 01:29, 3 March 2018 (UTC)[reply]

Not for lack of trying... [5] 78.0.254.206 (talk) 05:41, 3 March 2018 (UTC)[reply]

The point I was trying to make is in that link: "...whose low human populations do not allow human-dependent rats to survive..." and "Rat infested habitats, such as old farm buildings, are dismantled or destroyed." Rats would have an extreeeeeeemly hard time being pests of Neanderthals given that they were non-agricultural, very low density and didn't make any permanent buildings. Heaviside glow (talk) 23:02, 7 March 2018 (UTC)[reply]

In case you're not clear: the Norway rat is not from Norway, it's just an unfortunate misnomer. SemanticMantis (talk) 18:36, 4 March 2018 (UTC)[reply]

Thanks. I learn something new every day. Cosmopolitan pests never seem to be named correctly.. (like how American, German, and Oriental cockroaches are most likely African, Oriental, and not Oriental respectively) Sagittarian Milky Way (talk) 20:39, 4 March 2018 (UTC)[reply]

There are still parts of the world where a nice fat rat is prey, rather than pest. Animals only become pests when they are competing with humans for a common food source - which wasn't a significant issue before the start of agriculture. Wymspen (talk) 23:03, 2 March 2018 (UTC)[reply]

Homo neanderthalensis lived in Germany which was completely covered by Forest in that time and which is still home to predators like Owls, Weasels, Foxes and Lynxes which all hunt small Rodents. That is probably why Rodents propagation is so high. Actually they became a "pest" because their predators where thinned out as homo sapiens rose to higher culture, hunted excessively for their fur to make luxury clothing. Homo neanderthalensis most likely had little interest in all these small predators and so the rodent population was likely much smaller in the wild compared to their numbers in medieval and todays cities. --Kharon (talk) 00:41, 3 March 2018 (UTC)[reply]

The wood mouse is native to European temperate woodland and will enter buildings to find food given the chance. Not sure how long they've been around though. Alansplodge (talk) 12:07, 3 March 2018 (UTC)[reply]

Its range seems to include most of Europe: "In Europe it ranges north to Scandinavia and east to Ukraine. The wood mouse is also found in northwestern Africa and on many Mediterranean islands." According to the IUCN Red List of Threatened Species:

"The wood mouse has a large range that extends throughout Europe (with the exception of Finland and northern parts of Scandinavia, the Baltic and Russia) and parts of North Africa (Panteleyev 1998, Montgomery 1999, Wilson and Reeder 2005). In Europe, the species occurs from southern Europe northwards to Scandinavia; eastwards to northwest Turkey (Thrace and northwestern Anatolia), central Belarus, eastern Ukraine, and closely adjacent parts of the western Russian Federation (the easternmost limit of the species). In Africa, it occurs in the Atlas Mountains and north of them along the entire coastal plain. It is present on the majority of offshore islands including the British Isles, Iceland and numerous Mediterranean islands: for example the Aegean islands, Greece, some islands in the Tuscan Archipelago, Sardinia and Corsica, Italy. It occurs from sea level to 3,300 m in the High Atlas mountains."
"It is a very adaptable species, inhabiting a wide variety of semi-natural habitats including all types of woodland, moorland, steppe, arid Mediterranean shrubland, and sand dunes. It is also found in many man-made habitats including suburban and urban parks, gardens and wasteland, pastures and arable fields, and forestry plantations. It has an omnivorous diet including seeds and invertebrates. Although it can cause occasional damage, it is not generally considered an agricultural pest (Montgomery 1999)." Dimadick (talk) 19:14, 4 March 2018 (UTC)[reply]

Even today, the wood mouse is not a significant pest of humans. Heaviside glow (talk) 23:02, 7 March 2018 (UTC)[reply]