ANALI'TICA CHIMICA ACTA 339 ALIZARXN BLUE AS r\ SPECTI~IC REA(;13S'I ITOR THE GRAVIRIlXRIC l7ETERMINATION OF COPPER
Tn a previous paper' it was pointed out that the dye alizarin blue, for which, in view of its insolubility in aquous acids and alkali hydroxides, was assumed the chclate formula (I), reacts specifically with cupric ions. In strongly acid solutions, only this ion forms a blue crystalline precipitate when some drops of a pyridine solution of alizarin blue arc added*. The copper nlizarin blue formed, for which the chclate formula (II) was proposed, is extrcmcly insoluble, as shown by its resistance against highly concentrated mineral acids as well as by its formation from highly diluted solutions. In line with this, the copper alizarin blue is not altcrccl by sulfide ions (hydrogen sulfide or ammonia sulfide) and is also insoluble in potassium cyanide solutions which dissolve almost all wntcr insoluble normal and complex copper salts. * On addition of a pyridinc solution of the dye to ammomacal solutions of Zn-_, Cd-and Ni' salts, blue or blue green prcclpitates arc formed, which are easily destroyed by diluted mmeral acids. l?efeue?rccs p. 343.