23.3 parts of acetic acid (80%) are

23.3 parts of acetic acid (80%) are added to a solution of 55 parts of acetoacet-o-anisidide dissolved in a solution of 25.5 parts of sodium hydroxide (47%) in 450 parts of water at a temperature of 0.degree. C. The resultant slurry is reacted with 42.5 parts of p-nitro-o-anisidine previously diazotised with 45.4 parts of sodium nitrite (37%) and 56 parts of hydrochloric acid (36%) in the usual manner with simultaneous addition of sodium hydroxide solution (10%) to maintain pH 5.5-6.0. To the coupled slurry are then added 3 parts of dibutyl sebacate and 1 part of dimethylbenzyl-C.sub.12-14 alkylammonium chloride (100% active) and the mixture is heated to a temperature of 100.degree. C. and maintained at this temperature for one hour. The product is then filtered and washed with water under vacuum to remove soluble salts. The filter cake(still under vacuum suction) is mixed with a bacterial culture (10 ml of culture diluted to 100 ml with water)and vacuum suction is maintained until no further liquid emanates from the filter cake. The filter cake, without further washing, is then dried and converted to a powder by grinding. The powder is then passed through a 150 micron sieve.