Wikipedia:Reference desk/Archives/Science/2014 September 16

= September 16 =

Is it possible to make synthetic chlorophyll?
Plants photosynthesize by absorbing in water and carbon dioxide to make glucose and oxygen. Is it possible to make synthetic chlorophyll? 71.79.234.132 (talk) 03:18, 16 September 2014 (UTC)
 * See Chlorophyll. DMacks (talk) 03:26, 16 September 2014 (UTC)
 * I think he means a different molecule, or process, that accomplishes the same result. Not just duplicating chlorophyll (which wouldn't be enough anyway - you need the rest of the plant cell). Ariel. (talk) 07:48, 16 September 2014 (UTC)
 * For possible molecules that could substitute for chlorophyll, this (Xenology by R. A. Freitas Jr., section 10.2) might help. (Check out the book: it's a great read!) Double sharp (talk) 11:55, 16 September 2014 (UTC)
 * I suppose that if is be a synthetic glucose is always can be a synthetic chlorophyll.--Alex Sazonov (talk) 13:33, 16 September 2014 (UTC)


 * I don't know why you'd want synthetic chlorophyll, but if you're thinking of using it to make carbohydrates and oxygen, check out Artificial_photosynthesis. There have been some recent advances not yet documented in the article, search google (scholar) for /artificial leaf/ or /artificial photosynthesis/ to get some of the latest press releases. SemanticMantis (talk) 15:23, 16 September 2014 (UTC)

Reduction of salt’s melting point.
Im interested in moulding table salt. I wonder if there is a way to reduce its melting point? If so then how much lower? Also will it compromise its edibility? 85.141.201.92 (talk) 16:43, 16 September 2014 (UTC)


 * Unfortunately, not really. The melting point of sodium chloride is unlikely to be affected significantly by anything; you could perhaps lower it slightly by adulterating it with a lower-melting point substance, see freezing point depression.  But the change would only be a few degrees, not enough to make a big difference.  -- Jayron  32  16:57, 16 September 2014 (UTC)


 * Changing the pressure might alter the melting point a bit, but I doubt if the melting point can be changed by much.


 * Alternatively, I suggest filling the mold with salt crystals, pouring in fully saturated salt-water, then using heat to drive off the excess water. Repeat the process, adding more salt-water each time, until the mold is completely filled.  The salt from the salt-water should ideally fill the gaps between the crystals.  Note that this method will have a flat area on top.  If you want to mold a sphere, you would need to do it it two parts and then attach them together.


 * You could also just let the water evaporate on it's own. This wouldn't be good for a large mold, but if this is supposed to be edible, I would assume they are small, as humans should only consume a couple grams of sodium a day.  Also, affixing a long vertical tube on top of the mold would allow you to add more saltwater each time.


 * I'd put some type of cover directly over it to keep dust out, while the water evaporates, but obviously there needs to be a way for the water vapor to escape. Also, in case you don't already know, a mold requires a draft angle, so the salt can be easily removed:

+--+ TUBE COVER /       \     |    |     |TUBE| |   | +---+    +---+ MOLD COVER \  MOLD   / ++     HEAT


 * I would expect this type of molded salt to be fragile. If you need it stronger, you might consider some other type of edible chemical to hold it together better.  Water softener pellets seem to hold together well, so you could use whatever binder they use.   From my own experience, I've found that artificial vanilla dries to create a hard, tan-colored crust, but I'm sure there are many other options. StuRat (talk) 17:02, 16 September 2014 (UTC)


 * I've actually molten sodium chloride as is for a school physics project a depressing number of years ago. We used a big butane burner, a steel bowl and a plaster of paris mould. It looks pretty impressive, red hot and molten. It was also insanely dangerous, and in retrospect we were very lucky the mould didn't explode (though we did bake it out beforehand to remove any moisture). It worked just fine, but please do not try that at home. I guess you appreciate this and that's why you're looking to depress the melting point, but just felt I had to reiterate. Fgf10 (talk) 17:37, 16 September 2014 (UTC)


 * I suppose if you just need some kind of decorative edible salt, you could use Potassium Chloride instead of Sodium Chloride. It has a 770 degC melting point instead of 801 degC which helps a little...and it's supposed to be more healthy for you (with caveats).


 * Molding is only one of many approaches to making objects of a particular shape. I wonder if you could use an approach like 3D printing.  Make a tank filled with hot, fully saturated brine - lower a flat plate into the tank, half a millimeter at a time and use a laser to boil off the water where you want the object to be, leaving behind a layer of salt crystals.   Alternatively, you could use a subtractive process where you start with a large lump of rock-salt and use a computer controlled hot water jet to selectively dissolve the crystal and thereby carve out the final shape you want.


 * SteveBaker (talk) 17:54, 16 September 2014 (UTC)


 * You may also be able to shape salt by forging, subjecting it to high pressure. In the earth rock salt is quite weak and easily flows, and can probably do so with pressures of a few dozen megapascals. Graeme Bartlett (talk) 05:33, 17 September 2014 (UTC)


 * Indeed, rock salt at the surface will flow under its own weight when wet - salt glaciers in the Zagros flow, but only during the rainy season. Mikenorton (talk) 07:11, 17 September 2014 (UTC)


 * I suspect that when it is wet it is dissolving and recrystallizing. But you could attempt the same process in miniature. Graeme Bartlett (talk) 10:21, 17 September 2014 (UTC)


 * The deformation mechanism involved is a form of pressure solution - solution transfer creep. Mikenorton (talk) 12:32, 17 September 2014 (UTC)

Art vs engineering
Does engineering have elements of art in it unlike the pure sciences? Can you give examples of connections? — Preceding unsigned comment added by 90.198.211.63 (talk) 21:23, 16 September 2014 (UTC)


 * One concept is Form follows function. ←Baseball Bugs What's up, Doc? carrots→ 22:49, 16 September 2014 (UTC)


 * An example that comes to mind, related to BB's link, is military aircraft. Air Forces don't employ stylists for fighter aircraft, yet the ones that look the coolest are often the ones that perform the best.  Another example, more closely related to 1st question, would be rail locomotives.  The public's response to rail travel, especially in the early days, was in part due to how "cool-looking" the train was. Soon, locomotive manufactures realized that stylists coordinating with engineers was profitable. —(my primary source of railroad knowledge: Sid Meier's Railroad Tycoon (series)) — The Eiffel Tower is a better example.  The iconic shape and the combination of arches and triangles are due to engineering requirements rather than artistic ones; yet the artistic value of the resulting structure is obvious.  — 71.20.250.51 (talk) 23:31, 16 September 2014 (UTC)
 * As noted in the article, the artistic value of the Eiffel Tower was not obvious to many people when it was being built.--Srleffler (talk) 07:39, 20 September 2014 (UTC)


 * It really goes both ways. Another example by Gustave Eiffel is the Garabit Viaduct, where the taper from a horizontal cross-section at the bottom to vertical at the top is for sound engineering reasons, but looks cool as well.  On the other hand, the British SR Q1 class steam locomotive was soundly engineered to take wartime shortages of materials into account, and streamlining was irrelevant since it would not go all that fast; and the resulting design is considered one of the ugliest ever. --65.94.51.64 (talk) 23:54, 16 September 2014 (UTC)
 * We also have Structural art and Engineering. --Mark viking (talk) 00:14, 17 September 2014 (UTC)


 * The problem is that "art" is an exceedingly poorly defined term. You can't test or measure how well a particular piece of engineering (and I think fighter aircraft are a great example) constitutes "art".   Personally, I rather suspect the reverse.  We enjoy objects that function well as "art" even though they are the way they are for purely engineering reasons.  Not one inch of the design of an F16 fighter was engineered to make it look pretty - every inch of it is optimised to solve a particular set of hard engineering constraints.  The designers had little if any room to make "art" out of it.  That beautiful shape is mostly due to the original design requirements (range, weaponry, speed, manouverability) and the laws of physics.


 * That said, I feel that some engineering skills do have the feeling of art to them. Even in very 'hard' science fields like physics and mathematics, we have a feel for what the 'right' way to express a formula or other result that approaches "art".  We always say "E=mc2" rather than that c is the square root of E over m...the meaning would be identical - but it's somehow more beautiful as we conventionally express it.   In areas such as software engineering and electronics, you often hear people say that "It's not right until it's pretty" or "If it's not neat, it won't work".  Neither of these things are literally true - they are more like expressions of art.


 * SteveBaker (talk) 00:51, 17 September 2014 (UTC)

Unlike textbook stuff you do at uni real engineering often operates in areas where (a) the equations are unknown, and/or (b) the variables are unknown. Part of the art of engineering is coming up with a viable solution even without perfect knowledge of the system. Also, many parts are designed to look right, by eye, rather than calculated out to the n'th degree Greglocock (talk) 03:51, 17 September 2014 (UTC)


 * What course you do at Uni decides how you see things I think. For example, if you do a degree with engineering at its base, you will see things in terms of equations etc. If, however, you do a degree based around "industrial design", you will see things that are designed, but still engineered to fulfil its function. Automotive designers have to have some knowledge of engineering otherwise their products will look good but not work properly. In the UK the Design Council has awards for well-designed, well-engineered stuff. --TammyMoet (talk) 10:03, 17 September 2014 (UTC)


 * On the wording, recall "art" historically meant a skill, and we still may say something like "the golden gate bridge was artfully crafted" without causing much confusion. I think Tammy is spot-on, "design" can capture a lot of the intersection of art and engineering. You might like to read about the various works of Buckminster Fuller, who some hold up as a great figure in blending art/engineering/design. Also consider that architecture often incorporates aesthetics along with function in design goals. I also agree with Steve, you'll find many a professor in the hard sciences or math who will happily explain how much art goes into her work... SemanticMantis (talk) 15:42, 17 September 2014 (UTC)


 * Even in "pure science" the term elegant is commonly used to describe an equation, algorithm, engineering solution, etc. that is neat, simple and effective; therefore associated with the definition: "pleasingly graceful and stylish in appearance or manner".  [preceding based on an app that I don't know how to cite]   Alluding to Steve Baker's post, it is interesting to note that the famous "elegant" equation  E = mc2 wasn't formulated until after WW2, even though Einstein covered Mass–energy equivalence in 1905's  Annus Mirabilis papers.  There are many interim iterations, which rarely appear on t-shirts or bumper-stickers simply because they are not as "elegant".  WP does a good job covering this nomenclature history (without the t-shirt part) here.  — E:71.20.250.51 (talk) 17:56, 17 September 2014 (UTC)
 * That's a little picky. The article you cited credits that essentially the same equation was used by 1909, and "ε = Mc2" by 1914.  You can push it later and later by demanding the specific equation, specific letters, specific case of those letters, but that seems like a meaningless distinction to make. Wnt (talk) 21:21, 20 September 2014 (UTC)


 * Architecture is often quoted as a case where art and engineering are combined. Although it is possible to create buildings totally devoid of art, the resulting identical buildings look like prison blocks.  So, in most cases, some tweaks are made to the design to personalize each building.  Some architects, like Frank Lloyd Wright, emphasized the art part of the equation far more than others.  And medieval cathedrals were often impressive both for their engineering and artistic achievements, as were buildings from the Classical period, like the Greek Parthenon and Roman Pantheon. StuRat (talk) 14:39, 18 September 2014 (UTC)