a commonly used and accepted method described by kull a c eisman p c sylwestrowicz h d and mayer r l 1961 applied microbiology 9 538 541 using the ratio determined by q a is the concentration of compound a in parts per million ppm acting alone which produced and end point q a is the concentration of compound a in ppm in the mixture which produced and end point q b is the concentration of compound b in ppm acting alone which produced and end point q b is the concentration of compound b in ppm in the mixture which produced and end point when the sum of q a q a q b q b is greater than one 1 antagonism is indicated when the sum is equal to one additivity is indicated and when less than one 1 synergism is demonstrated the results demonstrating the synergism of these biocidal combinations are shown in tables i ii iii and iv table i minimal inhibitory concentration mic for pseudomonas aeruginosa q a ppm 0 0 935 1 87 3 75 7 5 15 q b ppm 0 u2212 50 100 250 500 u2212 750 u2212 u2212 1 000 u2212 u2212 1 500 u2212 u2212 2 000 u2212 u2212 2 500 u2212 u2212 u2212 5 000 u2212 0027 table ii synergy index for pseudomonas aeruginosa q a q b q a q b q a q b microorganism ppm ppm ppm ppm ppm si bacteria 1 p.