the frequent application of chemical methods in the examination of rocks, is enabled to improve and simplify the methods of microscopic chemical research. It must, however, be remarked that considerable skill and practice are required in all these methods. Phosphoric Airhydride.-In 1876, the author proposed to determine the phosphoric anhydride in apatite, under the microscope, by means of a nitric acid solution of ammonium molybdate. To the application of this reagent, Stelzner objected, as

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... uble silicates may give a similar reaction. The author has thoroughly examined the matter, and finds that it is always apatite which occasions the precipitation of the yellow granules, but t h a t the amount of the precipitate is greatly increased by the presence of soluble silica, so that one can be led to believe that the whole silicate consists of apatite, whereas the latter is present only in very small quantity. In order to detect the presence of apatite in a section with certainty, even in the presence of soluble silicates, the crystal to be tested for phosphoric anhydride is isolated by a glass cover, in which a hole is bored. The crystal is then dissolved in a drop of concentrated nitric acid, evaporated at a gentle heat, the residue decomposed with water, the solution removed by a pipette, placed in three drops on a glass and evaporated to dryness.