25 replies to this topic

[broadsword]

Basically you put the 500Mg tab on the scales when you have weighed out say 75g of Kno3. If it goes to 76g then you need to take some Kno3 out to get it back to 75g.

This is not correct as the 500mg is the amount of paracetamol in the actual tablet. Not the weight of the tablet! For instance some tablets you buy from say Tescos pharmacy will have paracetamol in them but also have other ingredients in too so they would still have 500mg of paracetamol in but they don't weigh 500mg!

[Creepin_pyro]

I think a more accurate way is to use calibration weights. A 100g weight will tell you more accurately how the scales are configured.

I thought the 500mg was reffering to the actual weight of paracetamol, and not the pill itself? Surely there will be a fair bit of filler in there?

Remember, scales work most accurately when completely level. Good ones will have adjustable feet and a spirit level, but there are other ways of levelling and positioning them for optimal performance.

[broadsword]

But you are very unlikely to get pure 500mg tablets! I very much doubt if it was possible for you to get these! as they need to hold together with something! rather like stars with the added dextrin!

[mnementh]

Hi guys,
how about keeping it simple. Assuming you live in the UK, then there is a simpler method of "checking" your scales. Go here;

http://www.24carat.c...s2000frame.html

A ?2 weighs exactly 12 grams. Variations on the coin weight scales should enable an accurate table of how YOUR scales measure up (no pun intended). Just add various coins (as shiny and new as poss., of course) and make up a graph of known weight against actual reading.

HTH,
Sandy

[blueflame]

Hi guys,
how about keeping it simple. Assuming you live in the UK, then there is a simpler method of "checking" your scales. Go here;

http://www.24carat.c...s2000frame.html

A ?2 weighs exactly 12 grams. Variations on the coin weight scales should enable an accurate table of how YOUR scales measure up (no pun intended). Just add various coins (as shiny and new as poss., of course) and make up a graph of known weight against actual reading.

HTH,
Sandy

omiting any scratches and dents of course.

[adamw]

And assuming it isn't forged!

You can buy calibration weights from most lab equipment suppliers, but they tend to be quite expensive.

[mrpyromx]

I know its a old thread, but I havnt been here in awiale. I know this is a uk forum, but a US $1 bill is exactly 1 gram. works great for calibrating.

[SwissTony]

omiting any scratches and dents of course.

Would this change the weight a lot??
if it was a dent, it would be the same weight but in a different shape???

[s2525]

Nah i doubt the weight would be changed by much,What about the mc donalds ice cream spoons thats what alot of dealers use to measure out there drugs (i think its 25mg) but i may be wrong on the weight but still it has to be fairly acurate

[Creepin_pyro]

Really, the only way to accurately test the calibration of your scales is with calibration weights.

I've even seen relatively cheap (<?60) scales that came with a calibration weight.

Using coins and similar things will give you a rough idea of how well calibrated your scales are, but if you're after accuracy, calibration weights are the only way to go. "consumer" scales tend to not work accurately with small weights anyway.

[Steve]

With pyrotechnics you don't really need to worry about having really accurate scales, that's more the relm of analytical chemistry. All that matters is relative propertions. If your scale thinks 60g of KNO3 weighs 75g, it will also think 12g of Charcoal will weigh 15g and 8g of Sulphur will weigh 10g. You still get the same 15:3:2 ratio.

On another note, 1 pence coins nearly weigh an exact 1/8 oz.

From dictionary.com

Accuracy - The quality of nearness to the truth or the true value
Precision - The ability of a measurement to be consistently reproduced

We are after precision in making fireworks, accuracy only matters when you are considering things directly relating to mass, such as moles, specific heat capacities etc.

[paul]

If your scale thinks 60g of KNO3 weighs 75g, it will also think 12g of Charcoal will weigh 15g and 8g of Sulphur will weigh 10g. You still get the same 15:3:2 ratio.

Well said. Didn?t think about that fact . Good explanation

[adamw]

But to be precise you also need to be accurate.