Table 3.

Actual factor levels corresponding to coded factor levels for 2^5-1 half-fractional factorial central composite rotatable design of response surface method

Variable (mg/L)	Actual values
	Code	-2	-1	0	1	2
NiCl2.6H2O	X1	0.250	0.50	0.750	1.00	1.250
ZnSO4.7H2O	X2	0.025	0.05	0.075	0.10	0.125
FeCl3	X3	0.025	0.05	0.075	0.10	0.125
K3BO3	X4	0.010	0.02	0.030	0.04	0.050
CuSO4.5H2O	X5	0.025	0.05	0.075	0.10	0.125