function ppm_calc(ppm,solution,purity) {
   //alert(ppm.value);
   //alert(solution.value);
   grams = solution.value * 1000;   // solution in grams
   prop  = ppm.value/1000000;       // translate PPM into portion
   alert('You will need ' + grams * prop * (100/purity.value) + ' grams of the product. For further explanations please see the example on this page.');
}