gems, spinel, blue spinel, chromophores, Åker, Sweden

The occasion for the present investigation arose from the desire to demonstrate the identity of the law of composition in a series of substances which, endowed with the same crystal form and composed of isomorphous constituents, must necessarily engage the interest of the chemist and mineralogist in equal measure. The existing analyses appeared unsatisfactory for this purpose, and the often very considerable differences in their results gave all the more reason to doubt their accuracy, since in none of them had any attempt yet been made to overcome completely, by means of a better method, the difficulties involved in decomposition, which so readily impair certainty and accuracy. Convinced of the importance of this circumstance, I therefore directed my whole attention first of all towards finding a simple method which, after a single fusion, would ensure complete decomposition, since this was a principal requirement for minerals of such hardness as spinel and chromite. To this end I carried out the following series of preliminary experiments, using crystals of blue spinel from Åker, which had been freed from adhering lime by dilute hydrochloric acid and, with the aid of the steel mortar described below and repeated washing, reduced to the finest powder; they had also been freed by hydrochloric acid from the iron introduced during grinding.