On the identification of chitin by its physical constants

The determination of the distribution of chitin in the animal kingdom is hampered by the absence of any test or positive means of identifying it. Gamgee, in his ‘Text-book of Physiological Chemistry,’ gives a list of structures of invertebrate animals in which chitin has been described. But when those cases are eliminated in which the identification has been based solely on the negative character of insolubility in caustic alkalis or weak acid, the revised list, as it appears, for instance, in von Furth’s ‘ Vergleichende chemische Physiologie der niederen Tiere,’ is greatly curtailed. It is true that chitin yields a characteristic decomposition product, the amido-derivative of sugar known as chitosamin, in definite proportions, but the amount of material available is not always sufficient to allow of the preparation of this product. In cases, however, where we have other reasons for suspecting the presence of chitin, the reducing action of the chitosamin resulting from the treatment of the original substance with sulphuric acid is a valuable confirmatory test. Under these circumstances it seemed that it might be worth while to make a determination of the specific gravity of chitin by the well-known method of a diffusion column. The specific gravity of any substance as thus determined stands in real and intimate relation to its chemical constitution, for the mass dealt with is always small and can therefore be rendered homogeneous by various cleansing processes. It is readily permeated be rendered homogeneous by various cleansing processes. It is readily permeated by the suspending fluid and the absence of any other sources of error may be ensured without difficulty.