Section holders or clamps for pressing out superfluous cement. Needle points mounted in light handles. Easy spring forceps. Mounting frame for centering section on glass slide. Small iron rod for singeing. Small camel’s hair brushes. Cutting pliers and forceps. Set of wooden section trays. Glass stopper bottles for benzole, benzine, turpentine and alcohol. Open neck bottles, with covers for two mounting liquids. Rotating mounting stand. Small microscope for testing transparency of section. Glass rods. Small squares and rectangles of plate-glass. Round, oval and square cover-glasses. Glass slides with ground edges. CHAPTER VI. CHEMICAL AND MECHANICAL TESTS. These tests may be necessary to confirm an optical determination or to assist in the differentiation of the closely related species of a group, as for example, the different plagioclases in the feldspar group. They may also be useful in the case of opaque substances. The ordinary chemical methods employed in mineral analyses are often not applicable, on account of the minute size of the mineral under investigation and the lack of sharpness in the reactions. Those methods[132] are to be preferred which produce crystallizations independent of the relative proportions of the materials taking part in the reaction and also of the physical conditions invoked. The tests can be made either on the crystal in a rock section or on the isolated crystal or fragment, the latter method being preferable when possible. CHEMICAL TESTS MADE ON CRYSTAL IN SECTION. The part of the section to be tested must be prepared by thorough washing with alcohol and benzole to remove all traces of balsam. If the section is covered, the cover-glass can be cut across with a diamond, and, after heating, the desired portion removed with a knife edge. Any portion of a section can be isolated by surrounding it with a rim of viscous balsam or by putting on a new cover-glass, in which a small hole has been made.[133] This hole can be accurately adjusted over the special portion of the section and the balsam removed by alcohol and benzole. The treatment of rock sections with ordinary acids, such as hydrochloric, may show the presence of easily soluble minerals[134] and carbonates, or distinguish silicates that are soluble with jelly, or produce etched figures on the minerals. _Test for Carbonates._ When only present in very minute grains the test can be made as follows: Cover the rock section with a drop of water and a cover-glass, then allow a drop of acid to slowly diffuse through the water film. The glass cover will prevent the escape of the gas bubbles[135] which will thus surely be detected. If necessary the section can be warmed by heating the projecting part of a suitable stand, placed under the section on the stage of the microscope.