[JamesCovalentBond]

Hey guys,

We were having a discussion among friends around the different ranges and types of measurements you can do with various states of matter: solid, liquid, and gas. (interesting stuff, right?)

When we came to the topic of solids, I got completely wrecked in my knowledge of how to measure small amounts of solids, (like think milligrams). 

So my question to you guys is how exactly would you measure small amounts of a solid like grain in the milligram level and still have a solid at the end of the measurement?

For example, if you know you need to measure out 6mg of fine grains, baking soda, or a vitamin, how exactly would you be sure you can do it? Would you add it to water? Would you measure with a really nice scale? And then how could you make sure you can convert it back into a solid again after measuring if you have to add it to a solution?

Any help would be greatly appreciated 

[Arkcon]

Some of your questions are easy, and some are hard to understand.  Basically, if you want to measure 6 mg, or 10, or even 20, you do it ... very carefully.  First of all, you have to have a proper balance (a scale is what us Yanks call a ruler, and that confuses people -- so get in the habit of calling it the balance.)  It should be rated for that low level, have its calibration checked at that level, by professionals often (say twice a year or quarterly) and by the user casually, every day.  Calibrated weights are used for this purpose, and they need an annual check.

Beyond that, you just weigh carefully.  You try and try until you get it right.

I don't really understand where you're going with dissolving in water and then getting it all back.  That's too far out there.  You'll have to explain that better.

[JamesCovalentBond]

Thanks for the response Arkcon!

I apologize for being vague, I wrote that thread late last night.

So the example we were using was like, say how would they measure out the ingredients in a Centrum or other multivitamin. Like say you wanted 6mg of Vitamin C and you need to measure out the original powder for 6mg. How would you measure out that small amount at such a large scale? It boggles my mind!

[Corribus]

Well, for one thing Centrum isn't weighing out the ingredients 1 tablet at a time. They're making millions (or whatever) of tablets from a single batch.

Aside from that, there are balances that can measure incredibly small amounts of material.

E.g., http://en.wikipedia.org/wiki/Quartz_crystal_microbalance

Obviously, the more sensitive balances are... more sensitive! To room vibrations, static electricity, and so forth. Not to mention they are expensive. Even a good quality analytical balance can run you thousands to tens of thousands of dollars.  Generally if you're making a mixture it's far easier to weigh out large amounts, make your mixture, and then dilute. But this isn't always possible...

[JamesCovalentBond]

Thanks Corribus!

I never even knew about quarts crystal microbalances, those are really cool.

I wonder how places work with small amounts in batches like that. I guess you could maybe combine all the powders together into a big giant even mixture, then take small amounts out.

Like say you have 4 different powders into a big container in even amounts (say 1000 grams total), mix it, then if you take 1 gram out, you could say that it contains .25 grams of each powder.

Im not sure if that makes sense 

[billnotgatez]

@JamesCovalentBond
Mixing (process engineering)
http://en.wikipedia.org/wiki/Mixing_%28process_engineering%29
Does this help?

And
If you can assume thorough mixing
Then I would think that measurement error would be statistically minimized with larger batches.