modified 05Nov2003 (Prof. Head-Gordon) see below
Discussion: see pp. 184 of D.C. Harris, Quantitative Chemical Analysis, 4th Edition (p177, 5th edition) (p105, 3rd edition).
Modification, Prof. Head-Gordon, Chem 1A, Fall 2003
double concentration of both reagents,
add 1/2 of thiocyanate solution to FeCl3 solution,
add remainder of thiocyanate solution,
noting change in appearance
add NaHPO4 and note color change