UV/Visible spectroscopy has been used as a method for determining the effects of salt and urea on two water soluble reactive red dyes in solution salt has the effect of increasing the increasing the degree of aggregation of the dye species present within the dyebath.This is shown by the decrease in the max
of both the monomeric and, to a lesser extent, the soluble aggregate species of the dyes. Urea has the
converse eect to salt, in that it increases the concentration of monomeric species in solution. This is evidenced by the increase in the max of the monomeric species relative to that of the soluble aggregate species. This technique may be used to assess the salt/urea sensitivity of reactive dyes and thereby help to de®ne conditions for their ecientapplication to cellulose.