Could someone tell me about how many mL of potassium dichromate crystals equals 1g?

Discussion in 'Alternative Processes' started by paradine, Aug 4, 2011.

  1. paradine

    paradine Member

    Messages:
    9
    Joined:
    Sep 12, 2010
    Location:
    London, UK
    Shooter:
    Multi Format
    This may seem like a stupid question but I recently bought a kitchen scale and it doesn't like low weight measurements at all and I have no way of telling measurements of almost anything under 10 grams..

    So as the title suggests could someone tell me about how many mL of crystals equals 1 gram?


    Thank you in advance.. I need to find a better scale.
     
  2. Worker 11811

    Worker 11811 Member

    Messages:
    1,626
    Joined:
    Jan 29, 2010
    Location:
    Pennsylvania
    Shooter:
    Multi Format
    Wikipedia is your friend! :D

    http://en.wikipedia.org/wiki/Potassium_dichromate

    From Wikipedia: Density = 2.676 g/cm3, solid.

    Therefore, one gram would be approximately 0.37 ml. ( 1 ÷ 2.676 = 0.37369208 )
    This assumes that the crystals are small and uniform in size. You still won't get a very reliable measurement.

    The best thing to do is get a good laboratory balance, not a "scale."

    A kitchen scale is designed to measure weights in the range of a few hundred grams to a few kilograms. That's between 100 and 1,000 times larger than you are trying to measure. A kitchen scale probably won't measure anything less than 10 or 20 grams with any kind of accuracy. Furthermore, it resolve to 0.5 grams. Even then, expect only ± 1 gram of precision. When you are cooking, you don't need accuracy/precision to 0.01 gram. Why should a cook spend the money for something that will?

    All that aside, you MIGHT have better luck if you put some other weight on the scale along with the item you are trying to measure. That will bring the scale into its most accurate range.

    Stack a handful of coins on the scale so that it reads, maybe, 50 or 100 grams then press the "tare" button. You will set the display to zero and the scale will remember the offset. Be sure to include your petri dish or other measurement container in the tare reading.

    Even with all that, you'll be lucky to get within a gram of the true weight/mass of the thing you want to measure.
     
  3. bsdunek

    bsdunek Subscriber

    Messages:
    1,361
    Joined:
    Jul 27, 2006
    Location:
    Michigan
    Shooter:
    Multi Format
    You can't compare volume and weight unless you know density. Different materials have different densitys. You need to find a scale that measures small weights, as you comment. You could get something like the illustration below for less than $20 at: http://www.oldwillknottscales.com/proscale-lc300.aspx
     

    Attached Files:

  4. Worker 11811

    Worker 11811 Member

    Messages:
    1,626
    Joined:
    Jan 29, 2010
    Location:
    Pennsylvania
    Shooter:
    Multi Format
    You will probably find that the most accessible, accurate and easy to use scales will be found at places that sell reloading supplies to hunters and shooters. They need to measure small amounts of gunowder, quickly and accurately.

    http://www.midwayusa.com/viewProduct/?productNumber=814722

    To get anything better than that you're probably going to have to step up to a laboratory grade balance.

    http://www.affordablescales.com/scales_specs.asp?specs=3153&Adam_Equipment_TBB_610S

    (Not recommending "affordablescales.com" as a merchant. Just using it as an example. Although, I have ordered from "midwayusa.com" and found them to be a reliable company.)
     
  5. Mainecoonmaniac

    Mainecoonmaniac Subscriber

    Messages:
    4,042
    Joined:
    Dec 10, 2009
    Shooter:
    Multi Format
    Milliliter is a unit of volume and grams is a unit of weight. The best thing is to get a with finer units. I've heard of bakers that the make bread by weighing their flour. The reason is that humidity can affect the weight of the flour. So I'm not sure this is a good comparison, but it seems logical to me.

    Here's one online that will weigh 1/10 of a gram.
    http://www.meritline.com/gram-weight-digital-pocket-jewelry-scales---p-47801.aspx

    Good luck!
     
  6. R Shaffer

    R Shaffer Member

    Messages:
    167
    Joined:
    Apr 11, 2008
    Location:
    Santa Cruz,
    Shooter:
    Multi Format
    You could just take all your dichromate ( or maybe just 13g of it ) and make a saturated solution which is about 13%. It keeps just fine that way and is far easier to handle as a solution.
     
  7. edp

    edp Member

    Messages:
    198
    Joined:
    Oct 7, 2009
    Shooter:
    Multi Format
    Small pocket balances that weigh in fractions of grams are available for pennies on ebay.
     
  8. Mike Wilde

    Mike Wilde Member

    Messages:
    2,933
    Joined:
    Aug 10, 2006
    Location:
    Misissauaga
    Shooter:
    Multi Format
    either online, or the local 'head shop'

    I came up with a great little electronic unit at a auction that des 0.01g (though not totally repeatably) and does tare also, with a capcity to 50g. $20 at a liqudation auction.
     
  9. polyglot

    polyglot Member

    Messages:
    3,470
    Joined:
    Jun 12, 2009
    Location:
    South Austra
    Shooter:
    Medium Format
    Measuring crystals by volume will not work because even if you know the density of the solid (as per W1811), you don't know the packing factor, i.e. how much air is in there between the crystals. Seriously, look on eBay, there are plenty of scales like Mike Wilde mentions selling for peanuts.
     
  10. Photo Engineer

    Photo Engineer Subscriber

    Messages:
    25,908
    Joined:
    Apr 19, 2005
    Location:
    Rochester, NY
    Shooter:
    Multi Format
    Do not measure solid materials by volume. The error can be as much as 20% either way. I have posted considerable data on APUG when I tested this out about 2 or 3 years ago (or maybe more).

    PE
     
  11. mrred

    mrred Subscriber

    Messages:
    1,149
    Joined:
    Mar 8, 2009
    Location:
    Montreal, Ca
    Shooter:
    Multi Format
    If you are *really* stuck, you can make a stock solution. Take 10g (minimum you can measure) and add distilled water to make 100ml. Then just use 10ml of that to get 1g effective quantity.

    Be sure to use distilled water, as you want to keep the integrity.
     
  12. ebenostby

    ebenostby Member

    Messages:
    3
    Joined:
    Jan 15, 2007
    Location:
    Bay Area
    Shooter:
    Multi Format
    If I had some potassium dichromate crystals, I'd weigh a teaspoonful for you, which is what I think you're asking for. But R Shaffer's suggestion is a great one if what you're doing is making a solution for gum prints. Take some dichromate crystals, add enough room temp. water so that most but not all of the crystals dissolve. The solution will be 12% (if you're at 20ºC). Draw your solution from the top so you don't scoop up undissolved crystals.

    If you want just a rough guess, it's somewhere around 1.5 g/ml, so a teaspoonful should weigh 7 or 8g.
     
  13. smieglitz

    smieglitz Member

    Messages:
    1,941
    Joined:
    Oct 18, 2002
    Location:
    Climax, Michigan
    Shooter:
    Large Format
  14. edwardpan

    edwardpan Member

    Messages:
    1
    Joined:
    Oct 27, 2012
    Location:
    13909 Magnol
    Shooter:
    Sub 35mm
    Just to say accuracy, if you want a really good one, you gotta shell out quite a few hundred bucks. I just needed a good quality at best price, so that's why I got a better one from Elite Scale which is perfect for what i need!