ch lor ic ▁acid ▁solutions . ▁This ▁property ▁is ▁used ▁in ▁the ▁first ▁stages ▁of ▁the ▁separation ▁of ▁rad ium ▁from ▁b arium ▁by ▁fraction al ▁cry st all ization . ▁Rad ium ▁ch lor ide ▁is ▁only ▁sp aring ly ▁sol ub le ▁in ▁a ze otrop ic ▁hydro ch lor ic ▁acid ▁and ▁virt ually ▁ins ol ub le ▁in ▁concentr ated ▁hydro ch lor ic ▁acid . ▁ ▁G ase ous ▁rad ium ▁ch lor ide ▁exists ▁as ▁Ra Cl 2 ▁mole cules , ▁as ▁with ▁other ▁al kal ine ▁earth ▁metal ▁hal ides . ▁The ▁gas ▁shows ▁strong ▁absor ptions ▁in ▁the ▁visible ▁spectrum ▁at ▁ 6 7 6 . 3   nm ▁and ▁ 6 4 9 . 8   nm ▁( red ): ▁the ▁dis soci ation ▁energy ▁of ▁the ▁rad ium – ch lor ine ▁bond ▁is ▁estimated ▁as ▁ 2 . 9   e V , ▁and ▁its ▁length ▁as ▁ 2 9 2   pm . ▁ ▁Con tr ary ▁to ▁diam agnet ic ▁b arium ▁ch lor ide , ▁rad ium ▁ch lor ide ▁is ▁weak ly ▁param agnet ic ▁with ▁a ▁magnetic ▁sus cept ibility ▁of ▁ 1 . 0 5 . ▁It ▁also ▁diff ers ▁from ▁b arium ▁ch lor ide ▁by ▁the ▁fl ame ▁color , ▁which ▁is ▁red ▁as ▁opposed ▁to ▁green ▁for ▁b arium ▁ch lor ide . ▁ ▁Us es ▁Rad ium ▁ch lor ide ▁is ▁still ▁used ▁for ▁the ▁initial ▁stages ▁of ▁the ▁separation ▁of ▁rad