The separation and estimation of small quantities of manganese in the course of exact analysis of igneous and metamorphic rocks has long presented a difficulty. The element is almost universally present, in amounts varying from a few hundredths of one per cent. to over one per cent., the higher figure being reached in the basic rocks, especially in those rich in ferromagnesian minerals. In the ordinary course of analysis, if no special method be adopted to separate and remove manganese, this element tends to be distributed between the 'ammonia precipitate' and the lime and magnesia. It has been shown by G. Steiger that when the usual methods are employed, the manganese tends to be distributed in a quite haphazard way among the three precipitates; no definite proportion is retained by any one of them, although as a general rule most of the manganese is found with the magnesia and least with the lime.