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Re: Sodium Hydroxide in local drinking water.

>Roger Miller wrote:
>. . .  in ppm of *nitrogen*, not nitrate;
>10 ppm of nitrogen is equivalent to 44 ppm of nitrate,
>and that's how we usually measure nitrate in aquariums.    (. . .)
>I am now confused.
>I thought that one PART per million means
>by the EACH, rather than by mass.

ppm refers to parts per million in whatever unit you are measuring in, be 
that mass, volume, frequency, whatever. ppb is parts per billion, ppt is 
parts per trillion, etc. It *is* by the each, but by the *each unit*, and a 
unit doesn't necessarily mean "one" of whatever you are measuring. Remember 
that the "parts per" is really a measure of concentration of the thing of 
interest with respect to how many other things are in the mix. Nitrate 
contains more than just nitrogen, so if you want the concentration of the 
*nitrogen only* you have to allow for the oxygen present when you determine 
the concentrations since the oxygen present in the nitrate effectively 
lowers the concentration of nitrogen in a given volume OR mass since the 
oxygen takes up both space AND weight.

James Purchase has already done way better than I could with the chemistry 
explanation so I'll leave that one alone :-)


Waveform Technology
UNIX Systems Administrator