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Posts posted by Externet

  1. Hi.

    Just found out that acetic acid (vinegar) applied onto recently scraped magnesium will bubble and fizz. It will not happen on aluminium.

    That's a household chemical easy to try with.

    ¿Does it make sense? I will try later myself... :)



  2. Hi.

    Re-trying to reply, as the text dissapeared while posting...


    Try a black-matrix LCD VGA display (I have a couple around, has normally shut pixels and will open the commanded ones) with the backlight panel removed, driven on a .pps -slide show- PC program to select a sequential chain of apertures and its locations.

    I do not see any problem with the source being infrared, but cannot tell for sure what opacity would be achieved. With plain white light they are not that much of opaque, it may actually be better with IR, or polarized IR!


    Good luck,

    Miguel :)

  3. Hi calbiterol


    Then it would be a flood infrared source, or a divergent laser..

    Put your bib on ; the shutter array from Flixel is here:




    And you may use Thin-Film-Transistor TFT if LCD is not desired :





    Miguel :)


    On the post pre-view the long Flixel link did not show up complete; trying again:




    -If does not show well, search for Flixel and electronicproducts-

    or shutter array and electronicproducts

  4. Hi.

    Cannot find how to discern if an unmarked automobile wheel is magnesium or aluminium.

    Any sure way to test please ?


    If a drop of battery acid is applied to an alloy rim, what reaction, color, etc. is expected if aluminium or if magnesium ?


    Or any other simple way to tell ?




  5. Hi calbiterol.

    What dimension is the preferred for the grid array, and how many vertical x horizontal cells ?

    Is 1mm² per cell small enough ?

    Is the laser focused to a cell or floods the array ?

    What is the preferred intercell gap dimension ... 0,1mm?

    What transparency range from closed to open (light transmissivity at both states)?

    What shutter speeds ?


    Same project appeared in other electronics forum about a year or two ago. It may be called a shutter array



    Am from Barcelona, pretend to know something, sometimes.

  6. Hi.

    Battery was an improper term, it will be a single cell (two rods or plates) protuding from a PVC pipe housing the electronics, exposed to seawater flow, submerged at no less than 10 feet depth.

    A photocell turns the unit off at nights.

    What would be the reaction ? If C and Zn, Na+ and Cl-



  7. Hi everyone.

    From what I remember, the highest electronegativity differential between two metals, the larger the voltage obtainable in a battery when those metals are used as its anode and cathode. Did I remember well?


    Using easy to get and cheap materials; as aluminium, copper, iron, carbon, lead, zinc... which two would yield the highest potential ¿lead and copper?

    Am trying to build a simple seawater cell to activate an ultrasonic beacon at expense of the electrodes. :rolleyes:


    An electronic circuit transforms the cell output to a higher voltage for circuit operation. Current capability is proportional to electrodes area.



  8. Hi.

    How many millions of years has our sun been burning ?... All that mass reduction being consumed to radiate energy for that lenght of time, has reduced its gravitational force attraction, and keeps happening, is it?

    Then, its pull is not a constant !


    For the earth to maintain orbit on a decreasing solar gravity pull, the orbit diameter has to continuosly diminish accordingly, does it ?

    Or the orbiting speed slowing, does it?


  9. Hmmmm.


    Naming as a compass the points on the drawing to have some reference...


    Being N&S an independent voltage source from W&E ; the positive S is such only respect to negative N.

    The positive S has no potential respect to either W & E and no arcing should occur in that direction.


  10. Hi.

    If I understand the graphic, the high voltage sources being paired in diagonals, the double arcing will occur in cross fashion, as sources are independent.


    Very good question, I suspect there will be collision of the arcs. No attraction, no repulsion, just crossing paths sharing a central point.


    Start edit, adding : <Re-thinking,... each arc creates a magnetic field which would affect the crossing point position of each other by forced deflection, and the polarity would determine if one arc passes above or under the other on direct current.

    Then there would be repulsion or attraction due to magnetic and not to electric fields.

    If alternating current, there would be a alternating cross path above and under.

    A similar behavior is an oscilloscope in x/y mode. Vertical defflection plates do not affect horizontal deflection plates electrically.> end edit


    Perfectly controlled conditions to do the experiment may be unstable. Please come back with observations.


    Another similar situation could be a neon tube cross, with independently powered straight arms.


  11. Hi.

    Once I browsed a ~400+ page book of formulas with the detailed procedures to manufacture hundreds of real generic commercial products, I remember was over $2000 and well worth them.

    Examples: formula and process to make brake fluid, detergent, artificial pigment, fly-sticky paper, deodorant, chlorine for pools from seawater... all kinds of things... It is not a household remedies book.


    Cannot remember the publisher, author, title.

    Any clues ?

    Thanks, Miguel

  12. Hi.

    A refrigerator compressor makes the best of all easy to get vacuum pumps. It really sucks ! :)

    You will be able to distill at room temperature.

    Many are discarded in good working condition. Get one, the size of choice, it is simple to plug and runs nearly silent and u$ually free. Keep its rubber mounts.


  13. Hi.

    It is a common suggestion to get rid of ice on a windshield by pouring cold water on instead of warm; there has to be a relation to the behavior :confused:


    Am from Barcelona too, and I pretend to know something... sometimes.



    ¿Why do my posts show a checkmark on rating? I have not done anything bad !...

  14. Hi.

    No.- water vapour, water, heat, cold, did not cause any alteration to the tinting; neither was affected by window cleaners nor showed any aging.

    At edges where the deposited film remained thicker, it was clearly observable micro puddling areas and dried beading. Was not water based.

    Imagine wetting an almost horizontal glass, water runs off but the lower edge forms a thicker non-running bead by whatever cohesion reasons.



    This was no Mickeymouse film job at all. Am very sure it was a liquid applied onto the glass surface. I had a conversation with the person that developed the product and there was not much magic in it; he just had his successful formula and made a side living out of it.

    The reason the glass had to be removed and laid flat to dry the ink was exactly because was so thin and fluid, that could not be applied to vertical surfaces as most of it would drip and make a big mess.

    Most customers were reluctant to have the glass dismantled from their cars, but the guy was soooo good, experienced and careful not to miss a clip or lose a screw and keep alignments that I had zero problems, zero complains about the job.


    The only similar process I am aware of, is gradual tinting in "degradé" done to eyewear lenses, were the lenses are repeatedly vertically dipped onto a solution, at gradually different dephts to dye the upper portion of the lenses darker. Seen it done. :)



  15. Hello.


    20 years ago, I had my car windows glass tinted overseas by a guy that removed the glass from doors, applied an ink to the inner surfaces by dipping -or spilling onto- (masking the exterior surface); let 24 hours to dry in a dust-free place and reinstalled them.

    The somewhat involved job result was a superb, yes, superb hard surface with no visual distortion, scratch resistant, UV filtering and unable to peel off. There was half a dozen hue choices in smoke, grey, clear, goldish, bluish, greenish...


    Several years later, by accident, a bottle of alcohol leaked inside my car parked under the sun and some areas of the ink "crackled" with the fumes.


    Does anyone knows how to prepare such product? Or ever heard of such process ? :confused:



    Miguel :)


    [edited: changed the word "crackeled" to the appropiate "crackled" to accurately describe the effect of solvent fumes]

  16. Hello, thanks for responding.


    Good question; I did not consider this dye to be too dangerous as was to be prepared by young experimenters with common sense in that book from the fifties/sixties; but realize the world has changed a lot since and it has to be taken in account.

    If there is a choice, would like to avoid caustic, poisonous and restricted access chemicals, maybe the regular compounds those complete hobby experimenter's chemical sets used to have many years ago, could be good, not the lean kits available of today.


    Cannot really answer the question properly, any suggestions or options would be fine.

    It may be something similar to fluoresceine, used to trace underground aquifers and their surfacing points; and believe fish and plants are not harmed from it.

    From the little I remember, it was a liquid as a result of some simple process of mixing a few chemicals.


    Miguel :)

  17. Hello.

    As a kid in the sixties I read on a chemistry and physics experimenter's book written for young readers, a simple process to home make something like what is now named rhodamine, capable of dying a whole pool water red with a few drops. Cannot find it now...

    Does anyone know how to make such a highly concentrated dye/ink/colorant with simple compounds ? Sort of remembering borax as one ingredient, but not sure after 45 years.

    Oh, those days with no television, no internet... and plenty of good books to discover !



  18. Hello.

    It's been over 30 years since my days at the university and have trouble thinking...

    I believe a catenary reflector has a focal area -locus?- instead of a focus point as a parabolic reflector has.


    Is it a circle ?


    The intention is to place a pipe of the same section at the locus of a catenary reflector trough, to be insolated and boil water circulating in it.

    The center of the locus must be centered between the ends of the catenary.

    The catenary lenght is 4 feet.

    What would be the correct catenary span or depth?




  19. Hi.

    Stolen from http://groups-beta.google.com/group/sci.chem/browse_thread/thread/e953efcde574ddf/dfadde77d600eed7 :


    The reason that stainless steels are corrosion resistant, even though

    they consist mainly of iron, is because they contain a minimum of 12%

    chromium, usually along with some other metals.

    Ordinary iron and steel alloys rust quickly because atomic iron is much

    smaller than oxides formed by interacting with atmospheric oxygen and/or

    oxygen dissolved in water. The oxides formed during rusting create a loose

    layer that flakes away, exposing fresh metal to the corrosion.

    Chromium, along with other metals ( such as nickel ), are added to

    stainless steel alloys to help improve physical propeties and corrosion

    resistance. The chromium in the stainless steel combines with oxygen,

    forming a very thin passive film of chromium-containing oxides.

    The sizes of chromium atoms and their oxides are similar, so they bind

    together on the surface of the metal, producing a thin oxide layer only

    a few atoms thick. If the surface is rubbed or damaged and the passive

    film is broken in air or water, more chromium oxides will immediately form

    and recover the exposed metal substrate surface, protecting it from

    further oxidative corrosion. Note that the oxide film is not physically

    strong, it just forms rapidly, and weakly adheres to the alloy, thus

    protecting the metal below from further corrosion. It can be disrupted

    and displaced easily by abrasion, so many common stainless steels aren't

    suitable for corrosive situations where the surface is continually swept,

    and special alloys, with other elements are used..

    The passive film requires oxygen to self-repair, so stainless steels can

    have poor corrosion resistance in situations where there is limited oxygen

    or other elements or species will compete with the oxygen. The smelly

    active sulphur species in garlic and onions; the volatile selenides in

    garlic, cabagge, and broccili; and also the chlorides in salty water will

    all attack and destroy the passive film of most stainless steels more

    quickly than the film can be repaired in a low oxygen environment.

    Some of the smelly compounds will bind to your hands ( onto proteins,

    lipids etc ) and will become non-volatile ( non-smelly ), but the number

    of binding sites is limited, hence any excess of smellies results in

    smelly hands.

    By binding to the metals in the stainless steel bar, the unbound smelly

    compounds on the surface your hands are transformed into non-volatile

    ( and thus non-smelly) compounds and complexes on the surface of the

    stainless. The new surface layer, which is weakly adhering and fragile,

    will be continuously abraded off by the active rubbing of the bar and

    replaced by oxides using oxygen from air or water.

    For many stainless steel items, especially those in contact with chemicals

    or water, passivating metal finishing processes are applied ( such as

    treatment with nitric acid ) when fabrication is complete. This ensures

    they start life with a good, thick layer of oxide. Otherwise corrosion

    may start in any crevices, scratches, or heat-affected areas ( welding ),

    and unprotective deposits ( eg smutty black sulphur layers ) may form in

    low oxygen environments, such as water.

    I hope the above is more understandable, and addresses your questions.

    (by Bruce Hamilton)

  20. Hi.

    At least this will be good for science fiction...


    The earth and our moon are in a very delicate and precise balance of speed and interacting gravity maintaining their position.

    In theory¿? any force applied to the moon can change its orbit a given amount.


    Assumming feasability of assembling a large enough upside down propulsion rocket on the visible side of our moon (or a smaller one for long enough time) and pushing it out of orbit until it is gone, gone...spiraling out no longer on earth's orbit.


    Yes, many catastrophic consequences implied here, but keep the imagination on.


    Doing the same with Titan, if a convenient atmosphere and water and other amenities are found there, bring it aiming precisely to start orbiting the earth as replacement.


    Well, another place to overpopulate and pollute would be available.


    With proper technology, time and calculus; is there any tiny chance for this to be not fiction some day ? :eek:



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