[Rhienne]

I need to test for phosphates in water as part of my advanced higher chemistry project.  I had originally come up with a method using tin(II) chloride and ammonium molybdate, but apparently the school no longer has any tin(II) chloride.  

Since I'm kinda running close to the deadline for this project(experimental work needs to be finished by the end of this week), I've been looking for another method, and came across one where 5M sulphuric acid, ammonium molybdate, rochelle salt solution and ascorbic acid(8.67g/500ml) are used as a reagent.  The only problem is that I can't seem to find out in what quantities to combine them and I'm not sure what concentrations of ammonium molybdate and rochelle salt solution to use.  I will need about 16ml of reagent for each of my water samples, of which there are 5. I was wondering if anyone could tell me how I would go about working this out.  Any help will be much appreciated ^_^