Keras
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Ohaus again (balances and hotplates)
I was thinking about buying a new balance, of the Ohaus Traveler series (prolly the 300g/0.01g). I understand Ohaus is one of the major brands of
analytical 'balances', so I think this is a reasonable choice?
Also, while I am at it, I saw they also make hotplates/mag. stirrers, and a dealer I usually buy glassware from has a 20% off discount currently
running on the Guardian 5000 series (€ 430 instead of 540). The device seems nice, do you think it'd be a good deal?
Thanks!
[Edited on 4-10-2021 by Keras]
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Oxy
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I was using OHaus scale with resolution to 0.01g and after it got damaged I switched to cheap 0.01g resolution scale and find no difference. I tested
it with some weights and seems totally OK.
Personally, until you want to get a scale for analytical purposes get the cheapest you can find and will fit your needs and requirements.
0.01g is way too low for analytical and if I were you I would just buy a cheaper one.
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Keras
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Quote: Originally posted by Oxy  | Personally, until you want to get a scale for analytical purposes get the cheapest you can find and will fit your needs and requirements.
0.01g is way too low for analytical and if I were you I would just buy a cheaper one. |
TBH, I'm super reluctant to buy Chinese made stuff. Even if it seems an overkill, I prefer to buy from a good brand and encourage European
fabrication. Right, that may seem a tenet for the rich, but I have always stuck to it.
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Sulaiman
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If you want european then Mettler Toledo,
Ohaus is NJ USA, but owned by Mettler Toledo.
PS Mettler Toledo has a USD34M factory in China 
I like cheap Chinese scales
but pay for one more digit than you actually need 
[Edited on 4-10-2021 by Sulaiman]
CAUTION : Hobby Chemist, not Professional or even Amateur
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Tsjerk
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I have a 20 euro 0.01 gram scale for years now and sure it can't actually measure anything below 0.05 gram, but I have been weighing the same coins
from the start and it gives exactly the same readings every time. Also the readings are what is listed for the coins on Wikipedia.
When it breaks I just get a new one for 20 euro.
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Keras
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| Quote: Originally posted by Sulaiman |
I like cheap Chinese scales
but pay for one more digit than you actually need
[Edited on 4-10-2021 by Sulaiman] |
Well, I have a lot of small graduated glassware, like 10 ml or so. If I want to measure densities correctly, for example, I find that 10 mg precision
is actually not an overkill.
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Oxy
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For really correct density measurement I would suggest to use a pycnometer. Not suitable for all liquids and needs to be well calibrated with
analytical balance. But once it's done and it's exact volume is known (never trust seller with that: I have 25ml which in reality is ~23.2ml) the
results are much better than those produced with graduated glassware.
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S.C. Wack
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$55 will get a complete, like-new Ohaus cent-o-gram to my door from ebay, but I already have one...I don't worry much about batteries or error codes
with it...maybe one has to be older than the digital age to understand.
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Keras
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| Quote: Originally posted by S.C. Wack | | $55 will get a complete, like-new Ohaus cent-o-gram to my door from ebay, but I already have one...I don't worry much about batteries or error codes
with it...maybe one has to be older than the digital age to understand. |
Oh I would be happy with a Cent-o-gram, but all the models sold on Ebay seem to originate from the US…
TBH, the major problem I have is finding a scale whose range goes to 300 or 400 g. I have a entry-level Kern mg scale, but it doesn't go beyond 100 g,
and this is much too cramped for all but microscale experiments (even a plastic beaker is already something like 10 g)
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Tsjerk
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500 gram 0.01
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Keras
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Yeah, you're right, all things considered, that might be the best option. Thanks for the suggestion.
[Edited on 6-10-2021 by Keras]
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MidLifeChemist
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You do realize the iPhone is made in China, right?
| Quote: Originally posted by Keras | | Quote: Originally posted by Oxy | Personally, until you want to get a scale for analytical purposes get the cheapest you can find and will fit your needs and requirements.
0.01g is way too low for analytical and if I were you I would just buy a cheaper one. |
TBH, I'm super reluctant to buy Chinese made stuff. Even if it seems an overkill, I prefer to buy from a good brand and encourage European
fabrication. Right, that may seem a tenet for the rich, but I have always stuck to it. |
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Keras
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Sure. I have an iPhone 5S. It's going to be 8 years old. If everyone did the same, there would be no rare earth shortage. :p
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Tsjerk
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| Quote: Originally posted by Keras |
Sure. I have an iPhone 5S. It's going to be 8 years old. If everyone did the same, there would be no rare earth shortage. :p |
Do you use it to browse the internet? If so, which browser do you use? I once excluded those devices from customer behavior analysis because the
website I was looking at didn't render at all anymore on "ancient" phones like that. SM should work fine though, as it is way more ancient
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teodor
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| Quote: Originally posted by Keras |
TBH, I'm super reluctant to buy Chinese made stuff. Even if it seems an overkill, I prefer to buy from a good brand and encourage European
fabrication. Right, that may seem a tenet for the rich, but I have always stuck to it. |
Keras, you encourage good quality traditions which was a part of European culture but at the same time, you are talking about measuring liquid density
using balances with 10 mg scale (which doesn't mean 10mg accuracy by the way). I see the contradiction. I think the quality culture begins with the
enjoyment of doing precise measurements and precise operations.
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Keras
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| Quote: Originally posted by teodor |
Keras, you encourage good quality traditions which was a part of European culture but at the same time, you are talking about measuring liquid density
using balances with 10 mg scale (which doesn't mean 10mg accuracy by the way). I see the contradiction. I think the quality culture begins with the
enjoyment of doing precise measurements and precise operations. |
I absolutely agree. I mean, measuring densities with a 10mg-precision scale is possible, given that you weigh around 100 g of your liquid (or more, if
your scale allows it).
My problem is that I often carry experiment at mini- (and sometimes micro-)scale level, so I have very little to weigh. That's why I use very small
volumetric flasks, typically 10 ml.
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teodor
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Check this: https://www.labmakelaar.com/product-category/all/saleable/ba...
It is used equipment. I bought my Kern PFB 200-3 there. I've got a printed test result with the balances also, they test it just before sending (the
test is putting control weights in different places of the balance's table for minimal, average, and near-maximal weight).
Generally, I find buying a good brand second-hand as a good option for a home lab.
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Keras
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| Quote: Originally posted by teodor | Check this: https://www.labmakelaar.com/product-category/all/saleable/ba...
It is used equipment. I bought my Kern PFB 200-3 there. I've got a printed test result with the balances also, they test it just before sending (the
test is putting control weights in different places of the balance's table for minimal, average, and near-maximal weight).
Generally, I find buying a good brand second-hand as a good option for a home lab. |
I wholeheartedly agree.
Do they ship anywhere in Europe?
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Sulaiman
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Calibration needs to be done at the place of use
or accept about 1ppm error per 6.37m (21 ft.) difference in altitude between places of calibration and use.
(+/- anomalies)
class A USP volumetric glassware has a tolerance of 0.02ml at 10ml
to calibrate your scales to +/-10mg you need only a class M1 test weight.
The cheap Chinese M1 calibration weights are not within specifications in my experience
https://youtu.be/kms21glg83M
but should be good enough for the +/-0.2% tolerance of the volumetric glassware.
CAUTION : Hobby Chemist, not Professional or even Amateur
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teodor
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Absolute weight is changing not only with altitude but with latitude also. But practically, we rarely need to know the absolute weight if we do all
measurements by the same balances for all tests and preparations, like in a case of a home lab. Reproducibility is what is really matters. And I am
following an old school that requires that all volumetric equipment should be checked and calibrated by balances. If you have a test set of weights it
is really nice but in any case, only one source should be used to calibrate all your instrument and make all standard solutions. So, if you have a
test of set weights use it to calibrate your balances and your balances to calibrate/check your flasks, burets, and pipets. Then use your balances and
calibrated flasks to prepare standard solutions. They will be the same quality if you use your balances even without calibration. So, the calibration
process of volumetric glassware is more important than the calibration of balances.
If you like to follow this school I highly recommend the book of Treadwell & Hall "Analytical chemistry", Volume II. It contains nice tables of
density of water (mentioning the difference between cm^3 and ml), buoyancy constants, the weight of water in the air (which is not 1g per ml),
temperature correction for volumetric glass, easy to use tables for glass temperature correction for flasks with different size. Following these
procedures is a nice experiment that opens the whole area of accuracy in chemistry (detecting the air archimedean force by balances is an eye-opening
event) and is interesting for a man who likes quality. Also, this kind of experiment shows which processes disturb accuracy more than others. For
example, I found that the hardest parameter to control is the cleanliness of a volumetric flask.
As for density measurement, the volumetric flask is not the proper instrument. The flask is for the preparation of a standard solution.
For density measurement most accurate results you can get only with burette. Practically, you can use a volumetric pipette which I think is a more
accurate instrument than a volumetric flask for this purpose. To weigh the last drop of liquid in the pipette you should touch the liquid in a beaker
placed on balances with the end of pipette, this way you can weigh the last drop without transferring it (all these tricks are described in the highly
recommended book of Treadwell). I remember I used 50ml volumetric pipette class B & 1mg balances to distinguish between 97% and 98% WFNA.
[Edited on 12-10-2021 by teodor]
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Sulaiman
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I agree that you can calibrate your volumetric glassware against your balance,
with or without calibration of the balance,
for calculations of stoichiometry and yield,
but
you can not use an un-calibrated balance to calibrate your volumetric glassware that you then use to measure density,
unless you used a liquid of accurately known density to calibrate your volumetric glassware.
.....................................
eg using a 0.1mg resolution balance calibrated with classE2 weights (+/- 1.6ppm)
and a 100ml classA USP volumetric flask (batch certificate = 100.021 +/-0.014 ml) (+/-140ppm)
I should be able to measure the density of water to better than +/-500ppm absolute (+/-0.05%)
I am happy if I get <= 0.1% absolute error with my best efforts. eg 0.997(1)
(diy ddH2O, heat & cool to remove dissolved gasses, impractically clean and dry glassware, calibrated (<0.5C error) thermometer, thermal
expansion and buoyancy corrections, stable room temperature)
The one time that I tried, I could not reliably distinguish between tap water and distilled water by density measurements.
(eg 350ppm TDS < 0.035% density error)
.........
PS ... I also agree that gravity varies with altitude, latitude and local anomalies
(I'm actually in a gravitational anomaly, that is not significant at my level of accuracy)
The variation in local gravity due to sun/moon/tides is more than order of magnitude below my measurement limits.
....
using a cheap 300g x 0.01g scale and cheap M1 weights I used to be confident to 0.25% error,
which is good enough for daily use.
[Edited on 13-10-2021 by Sulaiman]
CAUTION : Hobby Chemist, not Professional or even Amateur
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Herr Haber
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I bought a US Solid (Chinese, despite the name) a couple of years ago.
It's a 300 grams, miligram precision scale and I love it.
I read here and there US Solid scales are a bit of a gamble but I must have been lucky that day.
The spirit of adventure was upon me. Having nitric acid and copper, I had only to learn what the words 'act upon' meant. - Ira Remsen
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teodor
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Sulaiman,
I used double-distilled water (the second time with permanganate) to check my volumetric flask. I've got the full match (in the range of the accuracy
error) between the resulting weight and the calculation based on water density & all those tables.
This could be explained either:
A. My balances, volumetric flask, and water are accurate enough, that's why I've got the match.
B. My balances, volumetric flask, and water are inaccurate but all errors compensated each other and I've got the match between weight, volume, and
density.
As you can see, the probability of case B is lower. Even if it can be the case that can probably mean somebody used the same type of water (and which
is, for some unknown yet reason, is not clear enough) to calibrate the flask and all other explanations are even less probable. That's why I can
accept the hypothesis that I have accurate balances, flask, and water until I will find any contradiction using them. On that day I will try to check
the possible source of that error, but now I don't see the need.
Also, the match is possible only because we accept some range as an allowable error. In the case which I've described the cleanliness of the flask was
not perfect because some drops of water were sticking to the wall of the flask and it was hard to move them down. That's why I say that the accuracy
of my balances is better than the cleanliness of my glassware. After getting perfectly clean glassware the source of the error will be different. So,
I see the reaching of accuracy as a process that requires measurement, result analysis and process improvement.
[Edited on 13-10-2021 by teodor]
Your efforts in measuring the density of the water are impressive, by the way. I wish to repeat so accurate measurement one day, but I have chosen
0.001 g balances already, so I am unable to reach your accuracy. What I mean, I mean the importance to understand the source of errors in all
experiments, the dispersion of the result and for that, it's better to use the most accurate available instruments. But I decided 0.0001g balances are
too expensive for me if I usually have no time to clean glassware properly.
[Edited on 13-10-2021 by teodor]
[Edited on 13-10-2021 by teodor]
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Keras
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I'm going to buy a pycnometer anyway. They're cheap, like €17 for a 50 mL one.
I still need a good scale that will reach 300 g with 0.01 g tick.
I didn't thought about latitude and altitude things, but yeah, you're right. I wonder what value of g⃗ is programmed into the scales. 9,81 m/s²?
By the way, I have laid my hand on a 0-50 °C mercury thermometer, 0.2 °C DZ (graduations). Does that sound impressive?
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Tsjerk
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Nice thermometer!
Gravity isn't programmed into scales as they are calibrated against a calibration weight.
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