reference passing oil an oil passes the ball corrosion test if at least 75 of the balls have no rust pits on them at the conclusion while the passing oil also shows at least 75 passing balls at least 3 or 4 and the failing oil shows less than 75 passing balls at most 2 of 4 the results from a series of tests are shown in fig1 over three concentration ranges in all cases the concentration refers to the total corrosion additive concentration employed for the combination cases ratios between 1 part phosphate to 2 parts diacid and 2 parts phosphate to 1 part diacid by weight was used fig1 shows the total percentage of balls passing over all experiments for the three corrosion inhibitor systems over the concentration ranges shown in all three cases there was not a statistically significant trend over the three ranges shown at the 95 confidence level neither the phosphate or diacid ingredient used alone provided reliable protection from rust with fewer than half of the tests passing the minimum 75 specification however the combination of the two ingredients used at the same total additive treat rate exhibited a synergistic effect and increased the likelihood of a pass result greatly the results are shown below in table 1 table 1______________________________________ total balls total tests of balls of balls passing tests passing passing tests passing______________________________________phosphate 149 99 66 15 8 53 amine alonediacid alone 111 62 56 12 4 33 combination of diacid 252 213 85 25 21 84 amp phosphate amine______________________________________ this table demonstrates that over a range of turbo oil formulations the only case where consistent performance in the ball corrosion tests was demonstrated was for the combination of both ingredients a passing result could not be obtained consistently from either.