[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: Guaranteed analysis?

> From: Dave Kotschi <dkotschi at mindspring_com>
> Subject: Guaranteed analysis?
> I've got containers of magnesium sulphate, potassium sulphate and potassium 
> nitrate that I bought from Homegrown Hydroponics.  The sides of the 
> containers contain minimum analysis numbers.  What do these numbers 
> mean?  For example: potassium nitrate (KNO3) contains a minimum of nitrogen 
> (N) of 12%

	fair enough.

> and soluble potash (K2O) of 44%.  The nitrogen I understand but 
> how did we get from K_O3 to K2O?

	You _can_ regard KNO3 as a compound of K2O and N2O5 and K2SO4
as K2O and SO3.  "K20" would be the anhydride of KOH, N2O5 is the
anhydride of HNO3 and SO3 the anhydride of H2SO4.  Unfortunately
this stuck, when it came to the analysis of fertilisers.  They only
do it for potassium and phosphorous, not for nitrogen.

>  Is K2O in this mix in addition to 
> KNO3?  Similarly potassium sulphate (K2SO4) contains a minimum of soluble 
> potash (K2O) of 54%.

	There is no K2O at all in either.  It is just an archaic way of
stating the analysis.

>  Magnesium sulphate (MgSO4) contains a minimum of 
> magnesium of 10% and sulphur of 13%.  I think these last two minimums are 
> the relationship between the atomic weights of magnesium and sulphur.

	They are in about the right ratio, anyway.  There is water of
crystallysation in there too.

>  But 
> why no reference to soluble potash as there was in potassium sulphate?

	There isn't any potassium in it, and fortunately it isn't often
stated that way for magnesium.  This is the way, though, that 1 GH came to be
defined as 10 ppm CaO in water.

Paul Sears        Ottawa, Canada