Table 6. The results of variance analysis of the orthogonal tests.

Sources	Element	Type II Sum of Squares	df	MeanSquare	F	Sig.
Voltage gradient	Zn	185.678	2	92.839	2.130	0.320
	Pb	24.907	2	12.454	0.354	0.738
	Cu	337.518	2	168.759	14.218	0.066
	Cd	79.061	2	39.531	20.287	0.047
Proposing time	Zn	365.318	2	182.659	4.190	0.193
	Pb	278.884	2	139.442	3.969	0.201
	Cu	661.063	2	330.531	27.847	0.035
	Cd	90.683	2	45.341	23.269	0.041
Oxalic Acid concentration	Zn	1.967	2	.983	0.023	0.978
	Pb	224.432	2	112.216	3.194	0.238
	Cu	9.571	2	4.786	0.403	0.713
	Cd	1.718	2	0.859	0.441	0.694
Error	Zn	87.180	2	43.590
	Pb	70.272	2	35.136
	Cu	23.739	2	11.869
	Cd	3.897	2	1.949

Computed using alpha = 0.05.