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BlazeBall
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Decent laboratory balances?
Does anyone here have any recommendations on where to buy decent balances with an accuracy of 0.1g or better?
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aonomus
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That is a vague request (at the best). Asking for a 'decent balance with resolution <=0.1g' means nothing without stating the capacity,
and the accuracy.
(eg: I want to buy a car with 4 wheels or better)
If you want cheap scales with 100mg resolution with low capacity and linearity, you can try ebay or other cheap made in China products (not knocking
them, they have their purpose). If you want a scale with better resolution, higher capacity, and accuracy/precision, prepare to shell out some money,
try labx.com perhaps.
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entropy51
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My adivce is not to see how cheap you can be. Go with a recognized brand such as Ohaus. Ohaus also makes an excellent triple beam balance, but the one I have is not digital. 
For less than 120 gm I have an Acculab balance, good to 0,001 gm. I check it regularly with mg calibration weights and it's very close. But it cost
about $ 250 IIRC.
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BlazeBall
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Sorry, the capacity I need is only 100g which is why I neglected to mention it. I was weary of ebay because of many stories of said items failing
after a few dozen uses. Labx appears to be an American website so the postage would probably end up costing more than the item unfortunately. A UK
website is preferable.
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ScienceSquirrel
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Really it depends on what you want to do with the balance.
I have a set that are accurate to a claimed 0.1g over a 200g range that cost me £45.00. I have tested the linearity using piles of 2 pence pieces and
it is OK.
I have another set that are claimed to be accurate to 1g over a 5kg range. I have never bothered testing the linearity, they cost me about £30 from a
cook shop.
I use them for brewing, the small set weigh the hops, Irish moss, etc and the big set weigh the grain and other bulk ingredients.
If you are doing preparative chemistry on a ten to 100g gram scale the first set would suit you, if you are cooking up kilos then the second set would
be ideal.
Really pure reagents on a microscale you need accurate scales but if you are baking off sodium bicarbonate to make sodium carbonate and then reacting
it with cream of tartar to make Rochelle salt on a 100g scale then a few grams more or less will not matter a damn, the stuff will come out pure after
crystallisation!
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Lambda-Eyde
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I've been drooling over some of these balances. They're relatively cheap and affordable by a hobbyist.
Where I live, these "brand" scales cost in the thousands of NOK. For example, a Kern 420 g/1 mg scale costs a little below 10000 NOK including VAT,
with todays currency rate that's about 1600 USD. Buy used, you say? In a country with barely 5 million inhabitants the market for used laboratory
equipment is fairly non-existent...
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DougTheMapper
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I bought an American Weigh pocket scale for ~20 USD and it's accurate to .01g with a capacity of 100g. I have found that it needs frequent calibration
but will suffice for most projects without problems. Get it with the 100g calibration mass and check it against the most reliable balance you can get
your hands on. (As a student I have access to analytical balances and I have made small adjustments to my calibration mass)
I bought it on amazon.com here
Victor Grignard is a methylated spirit.
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SFL
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I've had good experiences with my palmscale 8. Mine is 300g/.001g. It was around $50. As for where, I just bought mine on ebay, but you can find it in
"real" stores too.
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Sedit
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Im sorry I know my post don't help much but this thread is bringing a tear to my eye missing my triple beam with accuracy down to .01. Rest in Piece
in the evidence room ol' trusty scale you will never be forgoten
Knowledge is useless to useless people...
"I see a lot of patterns in our behavior as a nation that parallel a lot of other historical processes. The fall of Rome, the fall of Germany — the
fall of the ruling country, the people who think they can do whatever they want without anybody else's consent. I've seen this story
before."~Maynard James Keenan
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BlazeBall
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Quote: Originally posted by Lambda-Eyde  | I've been drooling over some of these balances. They're relatively cheap and affordable by a hobbyist.
Where I live, these "brand" scales cost in the thousands of NOK. For example, a Kern 420 g/1 mg scale costs a little below 10000 NOK including VAT,
with todays currency rate that's about 1600 USD. Buy used, you say? In a country with barely 5 million inhabitants the market for used laboratory
equipment is fairly non-existent... |
Thanks for that website, the "My Weigh iBalance 500" scales look perfect for my needs. 
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kintekobo
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I recently bought a cheap digital balance on eBay from a company in Germany and have been very impressed with it. It arrived within a couple of days
and for the incredibly cheap price of £70 it is is both precise and accurate to the tolerance that I require.
Here is a picture of the item and the name of the eBay company selling it. It has a user guide in English but it is fairly basic, however I found I
didn't need it as it is quite simple to use.
I have no relationship with this company other than being a satisfied customer.
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UnintentionalChaos
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I own this scale in the 600g capacity, 0.01g readability flavor: http://www.scalesolutionsllc.com/m8/HRB--hrb-digital-analyti...
I bought it to replace a $30 0.1g readability jewelry scale that had terrible drift, ate batteries, and decided to up and die one day.
I purchased it several years ago through that company via ebay. I have been very satisfied with it's performance except that the glass doors are not
super easy to slide open on the windscreen (especially the top). There is generally very little drift. I slowly added magnesium filings to a beaker in
it last night over at least a half hour period (as I made them) and it did not drift enough to change the numbers between additions.
It even comes with a calibration weight.
The price has jumped around a lot over time. I think I managed to buy it at it's high of $260, and it was down at $180 for a time.
Department of Redundancy Department - Now with paperwork!
'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
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S.C. Wack
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I fixed an old Ohaus 311 (quadruple beam 0.01-311 g.) today and checked it with my 0.01-101 g. of class-Z Ohaus calibration weights. No one wanted it
because it would not zero. This was due to oxidation of the Fe in the shot under the pan, so this was easy to fix. Their triple beams that I've taken
apart used lead shot only.
Their manual does not specify accuracy/reproducibility at all. I could not get it to measure more than 20 mg. +/- off.
BTW the cheap calibration weights have been weighed with an old analytical balance - they're pretty good. I like the last generation of mechanical
analytical balances, but the weights tend to pop out during shipping of the ones that don't lock down, not to mention agate damage. They can be had
for very cheap.
Bonus BTW: if you don't want to pay exorbitant prices to make your Ohaus 700 triple beam weigh up to the 2610 g. that the label says, you can DIY: the
1000 and 500 g. accessory weights weigh 295.0 g. and 147.5 g. each.
[Edited on 23-1-2011 by S.C. Wack]
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Arthur Dent
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That's my next purchase. I don't want to go cheap too much, but a Ohaus bould be overkill for me. A small jeweler's scale that is accurate to .01 / .1
g with a set of calibrated weights should be fine.
Its uses would be mainly for precious metals titrations.
But if I get a good deal on a more expensive balance, i'll go for it.
Robert
--- Art is making something out of nothing and selling it. - Frank Zappa ---
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cnidocyte
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I got a 0.01g scale for £10 on a UK site.
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peach
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Pocket drug dealer scales get John's vote for 0.01g
I have posted about this before, but you would be surprised just how accurate those cheap drug dealer pocket scales are.
I spent hour upon hour checking one and various household objects against a calibrated 0.01/0.1mg balance I have; which usually
retails at £3k, as opposed to the £6.99 the pocket balance costs.
The results were that the £6.99 balance, reading to 100g at a resolution of 0.01g, is less than 1% off. IMPRESSIVE!
Neither was I using any form of draft shield on the pocket scale, or levelling it. I simply weighed a coin on the calibrated balance, then put it on
the pocket scale.
I produced big spreadsheets listing tens and tens of readings across the weight range for that, as well as checking how well things like change
functioned as a reference mass, how well balance beams made from rulers functioned as well as dividing things by eye and using digital kitchen scales.
Again, the results are far more accurate than you'd imagine, particularly the change. I seem to remember the error on a coin typically being something
like 0.05g, regardless of age. Also, because the error is periodic and even, stacks of coins cancel each individual mass error, so it goes down. The
error is not from wear and tear, but the Royal Mint dies wearing and the machine tolerances being adjusted. I can see the sine wave over the years on
the graph as it's kept in tolerance.
Digital kitchen scales are horribly inaccurate when dealing with a few grams. But their error drops to, again, about 1% as the weight goes over 100g.
Meaning, you can use the pocket ones for accurate work up to 100g, then the kitchen ones for hundreds to a kilo.
I then lost all of that work as I formatted the computer, so I need to redo it all. This time I may make a video of it as, with the fridge pumps, I
see the question of accurately determining mass appearing fairly often.
Here are the £6.99 pocket scales I was testing
Here is the balance I was checking them against - which showed a <1% error on the £6.99 balance. I did this work so others wouldn't have
to spend so much or could get more fun for their money. I was skeptical that these plastic things could even get close to their claimed resolution;
accurately. Particularly as they've never been calibrated and I've spilt agar and other rubbish on them, and knocked them around. But I have checked
it for you. And they do.
Balances come in fairly standard ranges of accuracy, 0.01g, 0.01/0.1mg and the micrograms. Both the 0.01/0.1mg and micrograms are significantly harder
to use in terms of maintaining their accuracy. They need mechanically isolating, to be level, temperature stable, left on for long periods of time and
in a humidity and temperature known environment, or the errors from those factors can swamp their resolution. Buying an accurate balance ain't enough.
I also discovered just how much that level of accuracy begins to infiltrate the rest of your work. As a very simple example, I can easily produce huge
changes in the mass I'm weighing depending on the amount of water of crystallisation present in a salt. If I produce the anhydrous salt, as soon as
it's out the bottle the mass will be visibly going up, quickly, on the 0.01mg/0.1mg balance as it picks up moisture from the atmosphere. It's trickier
than you'd imagine.
That piece of tinfoil, as another example, shouldn't really be there - turbulence.
{edit}I should check into having the 0.01/0.1mg one recalibrated. Then I could buy a pack of those pocket balances, check them all and pass them on
with a stamp of tolerance. Possibly with bits of nickel or stainless as a reference mass. Problem there being, 0.01/0.1mg and below recalibration is
usually pretty darn expensive.
[Edited on 24-1-2011 by peach]
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ScienceSquirrel
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I have a pair of electronic scales, 0 to 300g in 0.1g increments and 0 - 5kg in 1g increments and they are very good.
I use the small one for weighing out hops and yeast and the large one for weighing grain etc.
Given the other sources of inaccuracy in making beer on a 50 litre scale they are more than adequate for the job.
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peach
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That's an important point, that the finished result requires no painfully expensive level of accuracy in mass so you'll get a better result by
distributing the money around the other sources of error - e.g. buying a specific strain of yeast or hop.
Neither does a lot of chemistry need super high resolutions in mass when it's being run in hundreds of mls. I've seen results for organic work varying
by tens of percent in the yield, when it's being run with seemingly identical reagents and methods. The gross variation coming from the myriad of
other factors at work, like the hands of the person running it.
There's not much use knowing the end yield mass to 0.0001% error when there's orders of magnitude more variation in the process to begin with.
As I said the last time I mentioned this pocket balance thing, there are also other ways of obtaining precision beyond a high resolution balance. For
example, volumetric dilution. If you can weigh out 1g with a decent level of accuracy (pocket balance), and you have a volumetric flask, you can then
produce a stock solution that is much easier to divide up - with each aliquot delivering a far more precise quantity of your original 1g than the
balance could manage.
Part of the expensive of a digital balance is that it can measure a continuous range of masses. The volumetric method trades the continuous range for
precision in a known volume. E.g. a volumetric flask has a line at 1l for instance, not a scale. And a bulb pipette for picking up an aliquot to drop
into the titration flask is the same.
If you're titrating something, it doesn't matter if your solution is 1 mole or 1.2 mole, so long as you know the molarity well.
[Edited on 24-1-2011 by peach]
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ScienceSquirrel
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I agree with Peach, if you are doing preparative chemistry on a 5 - 25g scale then a scale reading to 0.1g is more than good enough.
The error is going to be around a few percent or hundreds of milligrams on the balance.
Suppose you have purified 5g of aspirin from tablets and you react this with home made nitric acid and sulphuric acid from the hardware store to make
picric acid.
Your aspirin could be 95 - 100% pure depending on how careful you have been. How pure are the acids?
The changes in yield due the purity of the reactants and the management of the reaction conditions almost certainly outweigh the errors in the balance
used to weigh the reactants.
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S.C. Wack
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| Quote: Originally posted by peach |
Both the 0.01/0.1mg and micrograms are significantly harder to use in terms of maintaining their accuracy. They need mechanically isolating, to be
level, temperature stable, left on for long periods of time and in a humidity and temperature known environment, or the errors from those factors can
swamp their resolution. |
This does not apply so much to an electrobalance, such as the Cahn 25 etc. Their little weighing pans ("stirrups") are ungodly expensive for what they
are though. Quite possibly the most ridiculously overpriced product on the planet.
[Edited on 25-1-2011 by S.C. Wack]
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peach
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Build your own... 
Or, if you're good with electronics...
I'm afraid all balances are affected by the numerous instabilities in temperature, air pressure, humidity, the gravimetric field, electrical fields,
magnetic fields, vibration and so on, electrobalances included. Question would be whether or not it's a big enough effect to be bothered about in the
range you're interested in. For the pocket 0.01g balance, next to zero care is needed.
If a balance displays a stable reading, it doesn't necessarily mean it is the correct reading.
[Edited on 25-1-2011 by peach]
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S.C. Wack
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| Quote: Originally posted by peach | | I'm afraid all balances are affected by the numerous instabilities in temperature, air pressure, humidity, the gravimetric field, electrical fields,
magnetic fields, vibration and so on, electrobalances included. |
You can take your lecture elsewhere; the difference in using an electrobalance is obvious to those who've compared them. Which is why I made my
earlier post; not just for the hell of it. Static is their only function problem and this can be dealt with. They are degrees of magnitude less
sensitive to vibration and level especially. You push the tare button and it zeroes. If it is out of calibration you recalibrate it.
It does if you're weighing something of a known weight and it gives the same number over and over.
Also, search my earlier post for the words "so much".
[Edited on 25-1-2011 by S.C. Wack]
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peach
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The people who define the kilo and who make the balances for doing so seem to have a difference of opinion.
The microgram comparator used by BIPM; the people who have the IPK in their vault
The 0.1ug FB-2 balance they built.
Sartorius microgram balance, available with metal shielding to counter electrostatic fields, deioniser and a synthetic stone vibration damping table.
This is their latest version, which doesn't include a handle, but does include levelling feet. It's $20k+
The Mettler microgram balance. Note the sight glass for levelling. This is because mass is measured by the force it exerts, and the force is directly
related to gravity. If the mass isn't directly on axis, it's no longer a scalar value but a vector
| Quote: | | According to OIML R111 and ASTM E617-97 magnetism of materials used for weights are strictly regulated. Weights are made in varying qualities and they
are sensitive with regards to magnetism. To determine the magnetic characteristics of weights, as well as of other similar artifacts, a Susceptometer
is required. |
The standards for calibration also list room conditions.
This is the International Prototype Kilo (IPK), made in 1879 in London and then sent to France, it is a platinum / iridium alloy with a double
chamfered edge for dimensional stability. Platinum provides it with a substantial level of chemical resistance and the 10% iridium (also a platinum
group metal) makes it harder to scuff. The IPK was declared by international law to be the kilo, so copies are checked against it by
mass comparators (dual pans). The copy always display the error, not the IPK; due to the IPK being considered the definition. The dual pan comparator
measures the incremental error between the two, not the absolute mass of the copy alone. The IPK is very rarely outside those three bell jars.
Countries buy copies and then maintain them, using those to calibrate their country's balances. There are six primary copies in the vault with the
IPK. Calibration certificates are available with traceability back to the IPK, for when mass matters.
In an attempt to put a finite measurement on what a kilo is, the Avogadro project chose to use spheres of silicon, as the semiconductor industry can
produce ultra high purity, defect free, monocrystalline boules of it across the globe. Two years worth of polishing and error cancelling later... the
lattice spacing of the silicon can be measured with X-ray diffraction and then the sphere's size by interferometry
To end the discussion for good, work is under way to produce a Watt balance to replace the fallible masses with a scientifically solid definition
based on physical constants. This has already occurred for the majority of other units. The metre, for instance, is now defined by the speed of light
in a vacuum, as opposed to a stick of platinum in the BIPM vault. The watt balance will define the kilo based on a mass's response to voltage and
current, both of which have also been defined by physical constants.
| Quote: | | You push the tare button and it zeroes. |
--->Pushes tare button on his balance.... HEY! It zero'd!
| Quote: | | If it is out of calibration you recalibrate it. |
With at least an in date, external microgram calibration mass.
[Edited on 26-1-2011 by peach]
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watson.fawkes
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Amateur electrobalances:
Homemade Microgram Electrobalance (erowid.org link; SciAm link not apparently available)
Down among the Micrograms (SciAm link)
Pretty impressive, actually. The second one (an improvement on the first) was able to see water evaporating from a centimeter of wet thread. These
articles pay close attention to error analysis and calibration and give a good idea of what it takes to attain high accuracy.
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S.C. Wack
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When I mentioned Ohaus beams as an option for y'all, I wasn't thinking new...you are allowed to buy used...they never need batteries. Support your
ebay sellers...ebay is all about buyers these days and it's tough being a seller anymore.
| Quote: Originally posted by peach |
The Mettler microgram balance. Note the sight glass for levelling. This is because mass is measured by the force it exerts, and the force is directly
related to gravity. If the mass isn't directly on axis, it's no longer a scalar value but a vector |
I don't know if that is a response to my post or what..the Cahn balances require none of that crap...ultra-fine measurement seems a bit off-topic
here...I'm not saying that Mettler and Sartorius balances aren't sensitive to problems...I thought I was saying the opposite...I own both brands, not
exactly those models...the old 0.1 mg. models of mine have enough drift problems...I have had opportunities to take isolation tables home but I have a
bad back...now let's look at the Cahn electrobalance which only requires no trucks driving by:
(also off-topic really because a used one that works may be a little pricey.)
(Cahn Instruments was sold to Thermo Electron...who became Thermo Fisher Scientific in 2006 and had no further interest.)
(I am unaware of any available manual for my model 25, but this model was its replacement.)
The Cahn C-34/C-35 is a very sensitive weight and force measurement instrument. It is designed for weights and forces up to 3.5 grams and is
sensitive to changes as small as 0.1 micrograms. The balance may be described as a force-to-current converter. It consists of (1) a balance beam
mounted to, supported by, and pivoting about the center of taut ribbon; (2) a torque motor coil located in a permanent magnetic field and also mounted
to the taut ribbon; (3) sample suspension fixtures; (4) a beam position sensor system; and (5) controls, circuitry and indicators (See Figure 1).
Weights or forces to be measured are applied to the sample (left) side of the beam which produce a force about the axis of rotation. An electric
current flowing in the torque motor also produces a force about the same axis which is equal and opposite to the force from the beam, if the beam is
at the beam reference position. This reference position is detected by the beam position sensing system. A greater force on the beam will require a
greater opposite force from the torque motor in order to keep the beam at its reference position. Therefore, the current necessary to produce the
required torque motor force is a direct measure of the force on the beam. The process of calibration allows this current to be measured in units of
weight (grams).
The Cahn C-34 or C-35 may be used in almost any location. It does not require leveling. However, the level should not change after zeroing. Try to
avoid exceptionally shaky tables, direct sunlight or drafty locations (such as near air conditioners). For ultimate microweighing, avoid locations
near equipment which generate vibrations such as vacuum pumps, air conditioners or heavy machinery.
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