Why do we need HNO3 for this???pls explain?

why is dilHNO3 added to test presence of chloride ions in limit test for chlorine?? limit test of chloride- a test and standard solution is separately taken,and to both of it AgNO3 is added and is followed by addition of HNO3 to both and distilled water is added to make the solution in both of the nessler's cylinder upto 50 ml.Opalescence formed is compared...this opalescence is due to the formation of AgCl.