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Thread: Water sample: Weight vs. Volume

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    Diver's Avatar
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    Question Water sample: Weight vs. Volume

    Here and there I use 5ml sample for chlorine testing. It comes in handy for anticipated high level where high accuracy is not required.

    Since it's less accurate than 10ml, I decided to at least get accurate amount of water to test. I figured I could use my scales for this since 5ml of pool water will be pretty close to 5g. To my surprise it wasn't so. It look like there was at least 10% disagreement.

    I decided to try to 10ml which is what usually used for this kind of testing. I'm using a test tube that came with a speed stir, but standard taylor k-2006 seemed to match it.

    When I pour 10ml into the tube (as accurate as I can judge, measuring at the bottom of a concave meniscus level), the weight showed 9.1g:



    When I poured exactly 10g, here is what level looked like:



    I'm a little surprised with discrepancy. I thought my scales might be off, but tests with a penny and a quarter were accurate to 0.05g.
    26K In-ground Vinyl Pool | Hayward DE4820/SP0710XR50 filter | 1.125 HP Dual Speed Hayward Super Pump | Aquasol Solar

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    jjslinger's Avatar
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    Re: Water sample: Weight vs. Volume

    I have two vials in my test kit, and I filled them to the 10 mL mark (bottom of meniscus) and weighed them on an electronic scale like you did. One came out to 9.9 grams, the other came out to 10.9 grams. My guess is that +/-10% accuracy is realistic for this sort of thing, and adequate for the sorts of measurements we are doing here.

    Don
    16K gal IG 16'x28' pebble since 2011; Pentair Easytouch; Sta-Rite Intellipro VS pump; Sta-Rite 400 sq. ft. cartridge (System 3); 6 Heliocol Solar Panels; Aquamatic Cover; Legend pressure-side cleaner with Hayward booster pump; TF100 Test Kit.

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    Diver's Avatar
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    Re: Water sample: Weight vs. Volume

    now i wonder if should feel it up to the level that showed 10gr instead of going to 10ml. since i know where 10ml is now..
    26K In-ground Vinyl Pool | Hayward DE4820/SP0710XR50 filter | 1.125 HP Dual Speed Hayward Super Pump | Aquasol Solar

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    jjslinger's Avatar
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    Re: Water sample: Weight vs. Volume

    Quote Originally Posted by Diver View Post
    now i wonder if should feel it up to the level that showed 10gr instead of going to 10ml. since i know where 10ml is now..
    Yes, if you want to up your game a notch, I don't see why you wouldn't do that. You have demonstrated that your scale is more accurate than your vial, so use your scale to calibrate the vial.....
    16K gal IG 16'x28' pebble since 2011; Pentair Easytouch; Sta-Rite Intellipro VS pump; Sta-Rite 400 sq. ft. cartridge (System 3); 6 Heliocol Solar Panels; Aquamatic Cover; Legend pressure-side cleaner with Hayward booster pump; TF100 Test Kit.

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