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Re: Is my Maths correct?

Posted by Larry Hoover on April 11, 2003, at 14:10:27

In reply to Re: Is my Maths correct? Larry Hoover, posted by bluedog on April 11, 2003, at 12:20:20

> > > Secondly I just so happen to have a 20ml measuring cup at home (came with a cough mixture I once purchased).
> >
> > Is it just marked at 20 mL, or does it have other graduations?
>
>
> It only has one other graduation at 1ml

That's not overly useful. :-/

> >
> > >So rearranging your formula around I calculate the following:_
> > >
> > > 2. If I dissolve 62.5g of my Mag Chlor in 1000ml of water I will get 150mg of elemental Mg in every 20ml dose....Right????
> >
> > Yes, but....how do you propose to measure out 62.5 mg?
> >
>
>
> Good point, I just checked out my kitchen scales and it would be rather difficult to measure out 62.5mg accurately. However doubling the amount to 125mg would be easier to measure out give or take a few grams but effectively doubling the strength of each 20ml dose to 300mg elemental Mg.

You could also divide the 500 mg in half by volume. Just measure the whole thing in cups or whatever, and mix half of it with one litre of water. That would make 5 mL (one teaspoon) equal to 150 mg Mg.

> > Alternatively, and using the ratio method, I've calculated that to get 150 mg Mg, from the whole lot dissolved in one litre, you'd need to take 2.5 mL, or 1/2 teaspoon. A baking measure will do fine.
>
>
> I can see your point, it would probably be a lot easier to buy a really cheap measuring cup with more graduations including 2.5ml, 5ml, 10ml etc to make things a little easier for me, or one of those sucky thingy's (I don't even know what you call them) with 0.5ml graduations) and to dissolve the whole 500g tub of my Mag Chlor into one litre of water.....Right?????

It's the simplest thing to do, all things considered.

> >
> > > This is the easiest way I can think of with the resources I currently have at home of getting a fairly accurate 150mg of elemental Mg per dose. (I'm not particularly worried about a few mg more or less each way).
> >
> > Your method depends on determining the right mass of Mg(Cl)2 in the first place.
>
>
> Your method sounds easier...just dissolve the whole tub into a one litre bottle or jar and then just use 2.5ml at a time to get my 150mg of elemental Mg per dose. Would it be necessary or desirable to to keep this bottle in the fridge or is room temp storage OK?

I can't think of any reason to keep it refrigerated, but it wouldn't hurt anything to do so.

> >
> > > 3. Please correct me if I'm wrong :) :). My maths has definitely slipped over the years...what you don't use you lose...Right?????
> >
> > That's why we invented calculators, non?
> >
>
>
> I did use a calculator but I initially had completely forgotton how to re-arrange equations but once I practiced a bit it all came back to me and I finally got there and this is the equation I came up with working with my limited measuring ability of only a 20ml measuring cup:-
>
> Xml=(60g)(20ml)/0.15

To be rigorous, there would need to be a g after the 0.15. Your units must divide out as well. This is how you check to make sure you've got the ratio rearranged properly.

> However this gave me a completely ludicrous situation where I would need to dissolve my 500g tub in 8 litres of water to get my desired result. To make it less wieldy and to make smaller one litre lots I simply divided 500g by 8 to get my 62.5mg of Mag Chlor to get the desired results.

Now I understand better how you got to where you did.

> So all in all your original equation ends up being a lot more helpful to me:) :). In other words
>
> Xml = (1000ml)(0.5)/60g

Again, just for the people following along at home, there needs to be a "g" alongside the 0.5.

> but I have simply replaced the 0.5 you used as an example with my target strength of 0.15 to get my intended dose of 150mg of elemental Mg per dose. You only need vary the 0.5 to 0.15 or 0.3 or 0.5 etc to get the ml you require for a particular dose strength of elemental Mg.

That's exactly right. You answer the question: "How much volume of this solution do I need to supply a given mass of Mg?"

> And applying this equation 2.5ml of the whole 500g tub dissolved in one litre does indeed give me a 150mg dose of elemental Mg (give or take a few mg either way due to my equipment not being lab quality accuracy) but it's good enough for my purposes. I can't argue with the experts:) :).
>
> Thanks again Larry
>
> regards
> bluedog

You're welcome. You might want to consider the alternative I mentioned at the top.....divide the volume in half, and mix one of those halves into one litre. That gives you a more manageable volume/mass relationship of 5 mL to 150 mg Mg.

Lar

 

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