 When purified by Schunck using sublimation and crystallisation, he obtained a result which suggested C14H8O4, but taking into account the analyses of metal derivatives as well, he chose C14H10O4 as the best result.The modern formula is C14H8O4.He found that oxidation of alizarin with nitric acid gave alizaric acid (phthalic acid) which on heating gave pyroalizaric acid (phthalic anhydride).