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- Jul 31, 2012
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Volumetric flasks are calibrated To Contain (TC). Graduates are calibrated To Deliver. If you want to check your cylinders you need 20°C distilled water and a decent balance. I worked in analytical labs most of my early years, the real genuine Nalgene graduates are quite good.I have a couple of those pharmaceutical (conical-shaped) PMP “cylinders” that mschchem pictured. Mine are not accurate!
I used 10ml and 50ml volumetric flasks to check all my others. I believe they’re accurate - 5 fills of the made-in-China 10ml flask just hits the line on my 50ml made-in-USA ONE. The 300ml, 600ml, and 1200ml Patersons are accurate, as are my 10ml glass and plastic cylinders and various smaller ones (25ml, 50ml, 100ml). But the conical one holds about 5% more than any of the others for a given volume mark.
Note that by “accurate” I really mean self-consistent because I have no way to verify absolute accuracy. Everything agrees for every comparison I’ve done except that conical one.
Does it matter? Maybe, maybe not. I have other options so I don’t use the conical one any longer. Fortunately I bought it many years ago before the price got silly.
I've been using the same plastic graduates for almost 30 years now. I've dropped them a few times but superglue always fixed them. I've been thinking of retiring them though since they have a lot of wear on them at this point. Battle scars I guess.
I bought a 25ml glass pipette a while back for measuring Rodinal but it reads reversed so I don't really know how to use it. Fill it all the way then push it back down? No idea. Anyone have a suggestion on that I am all ears.
My feeling on these things these days is you might as well get good ones. You'll probably have them the rest of your life.
I actually did my initial testing with distilled water and a trusted digital scale, all at the marked temperature. That allowed me to verify my 100ml graduate, which I then used as a transfer standard. It’s also how I found that my pharmacist’s graduate (conical PMP) was off by about 5%.Volumetric flasks are calibrated To Contain (TC). Graduates are calibrated To Deliver. If you want to check your cylinders you need 20°C distilled water and a decent balance. I worked in analytical labs most of my early years, the real genuine Nalgene graduates are quite good.
I love it! Pickyness is fun.I actually did my initial testing with distilled water and a trusted digital scale, all at the marked temperature. That allowed me to verify my 100ml graduate, which I then used as a transfer standard. It’s also how I found that my pharmacist’s graduate (conical PMP) was off by about 5%.
And yes, I know my pickiness level was on the high side, but I’m retired, it was Covid, and I was curious.
Good to learn about the "to deliver" markings. IIRC from college chemistry one should read a graduated cylinder, burette, etc, to the bottom of the meniscus. Odd that no one mentioned this.
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