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| Author |
Message |
| 24 new of 98 responses total. |
rcurl
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response 75 of 98:
| 
Oct 29 22:56 UTC 2000 |
It doesn't cure rapidly, meanwhile picking up dust (and leaves).
|
keesan
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response 76 of 98:
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Oct 30 17:18 UTC 2000 |
We will not worry then, as the porch warms up rapidly the next morning and
these boards are only being painted to act as a vapor barrier, and the plastic
on the porch should keep out the dust and leaves.
|
oddie
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response 77 of 98:
|
Nov 25 07:21 UTC 2000 |
This was asked in the agora item on candy, retailing and suchlike, but
to prevent drift I'll repeat it here:
Why are saturated fats solid but unsaturated fats liquid (in general)?
My recollection from chem class is that dispersion forces are greater
for some reason in straight carbon chains, but I haven't a chemistry
book on hand at the moment so I can't check this.
On a possibly related note, what happens to butter when one melts it
and then allows it to cool again? It changes color and texture, but
why, chemically?
|
keesan
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response 78 of 98:
|
Nov 25 18:38 UTC 2000 |
Heating butter and cooling it separates a layer of fat (on top) from a layer
of other things that dissolve in water and reflect more light. The top layer
is what Indians call ghee. It is less likely to burn than the dissolved or
suspended matter, and it keeps longer since many microorganisms cannot live
in pure fat (they need water and minerals and oxygen, which is blocked by the
fat). One method of preserving foods is to pour melted lard or butter or
olive oil into the top of the jar of hot food. You can bake the whole thing
in the oven for a while to sterilize it.
|
rcurl
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response 79 of 98:
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Nov 27 06:42 UTC 2000 |
Unsaturated fats have a lower melting point than saturated fats, in
general, for the same carbon number. Yes, it is because the dispersion
forces are greater for the saturated fats. A mechanical way to look at it
is that the rigidity of the double bonded carbons, which also introduces a
"kink" into the fatty acid, interfers with alignment of the molecules and
hence with crystallization.
|
oddie
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response 80 of 98:
|
Dec 3 07:16 UTC 2000 |
Thank you both.
I had heard of ghee but never knew what it really was. Today I looked up
hydrocarbons in my chemistry textbook (by someone called Steven Zumdahl,
if anyone's interested) but didn't find anything on b.p. and m.p. (I
suspect I overlooked it, but as I know the answer in about as much detail
as the book would probably give it hardly matters). Thanks again.
|
rcurl
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response 81 of 98:
|
Dec 3 21:55 UTC 2000 |
You probably didn't overlook it - elementary texts usually don't get
into the physics of phase changes except to note they occur, and maybe
some values as melting point is used to identify compounds.
|
keesan
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response 82 of 98:
|
Dec 3 22:15 UTC 2000 |
The best ghee is said to come from water buffaloes. Water buffaloes are also
found in Kosovo, where there are flat wet areas, and a fermented clotted cream
is made from the milk. I don't know how the war affected the animals.
|
dannyboy
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response 83 of 98:
|
Nov 8 13:26 UTC 2001 |
As for why saturated fats are generally solid, as opposed to unsaturated ones,
it is basically to do with the shape of them. The straight chain alkanes can
sit together more closely, resulting in higher Van-Der Vaals forces
(instantaneous dipole-induced dipole). There may also be hydrogen bonding
effects which are influenced by the double bonds.
|
keesan
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response 84 of 98:
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Feb 3 03:44 UTC 2003 |
Jim asks if ozone can pass through steel, as in refrigerator motors. He heard
that hydrogen can pass through steel.
|
rcurl
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response 85 of 98:
|
Feb 3 07:33 UTC 2003 |
No, ozone cannot pass through steel. Why? There isn't much ozone around.
Yes, hydrogen has dissolve in steel - leading to embrittlement.
|
gull
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response 86 of 98:
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Feb 3 15:46 UTC 2003 |
Most motors are vented to get rid of heat, though, so ozone can escape
that way if there's any arcing going on.
|
russ
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response 87 of 98:
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Feb 3 22:40 UTC 2003 |
The question in #84 betrays two misconceptions:
1.) There's no ozone in a refrigerator's cooling system.
Refrigerator motors are induction motors, which cannot create
ozone. The commutator sparking of brush-type motors makes
ozone; induction motors have no commutators or brushes.
2.) The creation of ozone requires free oxygen. There is
essentially no oxygen in a refrigerator's system.
|
rcurl
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response 88 of 98:
|
Feb 4 07:13 UTC 2003 |
3.) ozone is very reactive and would have been depleted by reaction
first IF any could have been formed.
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keesan
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response 89 of 98:
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Feb 7 01:08 UTC 2003 |
Jim says 'Yes' that answers his question. Now he wants me to help him set
up a database that will be used to record temperature, humidity, and electric
meter reading at various times of day, week and month, in DOS. (We are not
very far into Linux yet). Or maybe it should be a spreadsheet program. He
wants averages and graphs but also to be able to sort and filter. Are there
programs that do all this? I suggested finding programs that will import and
export text-format files (a pair of programs that you can move data between).
He wants to plot and calculate and see how it depends on time of day and
presence of housemates. Ideas?
|
rcurl
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response 90 of 98:
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Jan 8 06:48 UTC 2006 |
An hollow metal box that weighs 20 pounds is 1 foot on a side and hence
has a total (external) volume of 1 cubic foot. It is placed on the bottom
of a tank and then welded to the bottom completely around all four bottom
edges. The tank is then filled with water to a depth of two feet. With
what force is the box pulling upon the floor of the tank because of its
bouyancy?
|
sholmes
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response 91 of 98:
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Nov 20 02:29 UTC 2009 |
What is more ecologically damaging- using 2 styrofoam cup daily or using water
and soap to wash a steel cup twice daily ? Similarly are electric cars more
environment friendly, if the electricity used to charge the batteries was
generated by say a coal fired power plant ?
|
keesan
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response 92 of 98:
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Nov 20 02:48 UTC 2009 |
A coal fired plant is far less polluting than a gasoline engine because you
can clean the fumes at the source with larger and more efficient equipment,
also the fumes are generated away from where people are walking around.
I think electricity generation is also more efficient than gasoline engines
but you do lose something in transmission.
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rcurl
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response 93 of 98:
|
Nov 20 06:01 UTC 2009 |
Re #90: No one has been able to solve that problem in over 3.5 years?!
Re #91: Sindi is right about electricity. Its generation in a combined
cycle gas turbine (CCGT) plant is ca. 60% efficient, nearly twice that
of internal combustion engines. Also, it is more environmentally
friendly using natural gas.
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keesan
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response 94 of 98:
|
Nov 20 16:47 UTC 2009 |
Cars can also run on natural gas, which is less polluting.
|
rcurl
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response 95 of 98:
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Nov 20 21:12 UTC 2009 |
If you can find a natural gas station....
|
keesan
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response 96 of 98:
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Nov 20 21:40 UTC 2009 |
On Hiscock St. near the garbage yard.
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rcurl
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response 97 of 98:
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Nov 21 06:23 UTC 2009 |
Where else?
"Natural gas rises as viable fuel, but lack of infrastructure could
prevent use in consumer vehicles"
"Michigan has 13 compressed NG stations open to the public."
http://is.gd/50aKG
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tod
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response 98 of 98:
|
Jan 1 00:03 UTC 2010 |
I wonder how much acid rain would be welcome if it meant more ozone
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