loss is not an absolute figure as losses up to about 30 can sometimes be tolerated without weakening the foil too much for subsequent handling and processing the 20 level is a balance of sufficient foil strength for subsequent processing and very acceptable capacitance values these investigations at a 20 weight loss showed that increasing the sulfuric acid concentration up to about 20 wt sulfuric acid resulted in higher capacitance at any weight loss however above a 20 22 wt sulfuric acid concentration capacitance fell off quickly increasing the temperature also results in higher capacitance at any given weight loss and at a 20 weight loss each 5 u00b0 c increase in temperature particularly in the 90 u00b0 to 105 u00b0 c range raises capacitance by about 225 u03bcf in 2 for each temperature and etchant composition etching time for a 20 weight loss was determinated and foil residence time in the bath was set to correspond to such weight loss referring now to fig2 capacitance in u03bcf in 2 of foil is plotted against sulfuric acid concentration in weight percent at various temperatures using an etchant also containing 11 wt sodium chloride and 14 wt aluminum sulfate at 90 u00b0 c capacitance rose sharply between 11 and 14 wt sulfuric acid and increased at a more gradual rate to 17 wt acid capacitance remained fairly constant to 20 wt acid and then dropped off abruptly at 95 u00b0 c the results are similar except that all capacitance values are higher and the peak is narrower.