@nw7 thanks for the great guide!
I don't want to sound annoying, but I was only able to do this in a sub-optimal fashion and wanted to know whether you thought the results were still useful or not.
Didn't have distilled water on hand, so used store-bought spring water. The only cups I had only held 250mL, so used that amount of water in each.
The crappy scales I had only measured in 1g increments, so I used 3g of SN.
My SN was from a seemingly legitimate local chemical supplies website and advertised as 'Sodium Nitrite Food Grade 100% Pure'.
I had a syringe with measurements on it so was able to exactly transfer 1mL of solution from cup 1 into cup 2.
I used
these strips for testing the mixture in cup 2 using their instructions (one second dip, remove and shake, 1 minute wait, read). On the relevant colour chart for Nitrite, the result was the highest possible being 80mg/L.
So on the face of it that sounds like a very strong concentration of Nitrite, possibly even so strong as to overrule any methodological shortcomings, but will any of those shortcomings mentioned make this result inaccurate?
If so, I will aim to get some distilled water and some more precise scales. If I'm still only able to source 250mL cups, please advise whether I need to change the maths at all in future calculations. Maths really isn't my strong suit.
Thanks in advance for your input.
Autumnal
3g of SN, dissolved in 250mL of water.
Converting 250ml to L : 250/1000 = 0.25 L
So, you have 3g in 0.25 L.
So the concentration is 3 / 0.25 = 12 g/L.
Then you took 1ml of that solution.
So you took 1/1000 = 0.001 L.
0.001 L * 12 g/L = 0.012 g = 12mg
So the 1ml that you took contained 12mg
You then placed that into 250ml of water.
250ml = 0.25 L
So, you have 12mg in 0.25 L
So the concentration is 12 / 0.25 = 48 mg/L.
So you'll notice you're getting a x4 effect (since you're using 250ml), twice, so you're getting a x16 effect overall, combined with a L -> ml effect, since you're transferring 1ml over.
If the SN was 100% purity, then your test kit should have indicated around 48 mg/L.
However, if the amount of SN you used was closer to 4g than 3g (due to the accuracy level of the scales), then :
The first concentration would be 4 / 0.25 = 16 g/L.
The final concentration would be 64 mg/L
(you can check that by following the calculations above, but using 4 instead of 3)
In that case, if the SN was 100% purity, then your test kit should have indicated around 64 mg/L.
SO..... If you observed a result of 80mg/L then either something has gone wrong with the test, or the test kit is faulty (although I suppose another possibility is that you had about 4g in truth, and the test kit is not accurate enough to be able to tell the difference between 64mg/L and 80mg/L)
The x16 effect of using 250ml will cause any inaccuracy in the weight measurements to be heavily amplified.
So you would need to use accurate scales, and accurate measurement of the 1ml.
If your test strips can measure up to 80 mg/L, then I would do the following :
> Use 1 litre of water in each "cup" (actually, you would perhaps use bottles rather than cups)
> Use 10g of SN, and transfer 4ml from cup/bottle 1 to cup/bottle 2.
> This would mean you end up with about 40mg/L if the SN is 100% pure.
I use this approach because I think testing in the *middle* of the test range is better (see thread below, which explains the rationale behind that)
To get a better understanding of this test method in general, please take a read of this :
https://sanctioned-suicide.net/threads/sn-aquarium-purity-testing.34630/
Hopefully that ^ thread explains better how this whole test method works, and may allow you to design your own tests more effectively.
