Elementary chemical microscopy

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John Wiley & sons, inc., 1915 - Chemical microscopy - 410 pages
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Page 5 - This angle is obviously that of the cone of light rays whose apex lies in the optic axis of the microscope at the point where the axis passes through the plane of the object and the diameter of whose base is equivalent to the opening of the front lens combination of the objective. Dry objectives may be compared with each other with reference to their angular aperture. In general the angular aperture depends largely upon the diameter of the front combination of the objective, and usually in objectives...
Page 172 - ... directions of vibration (found always to be at right angles to each other) of the light rays which advance with maximum or minimum velocity and a third direction at right angles to the plane of these directions (corresponding to some ray with an intermediate velocity) are called Axes of Elasticity." * In the orthorhombic system the axes of elasticity coincide with the crystallographic axes. In the monoclinic, one axis of elasticity coincides with the b-axis, the other two axes of elasticity are...
Page 309 - Cd(CNS)2-Hg(CNS)2 in brilliant colorless, probably orthorhombic prisms, usually several times as long as broad but the appearance of these prisms varies with the conditions which obtain at the time of their formation, as, for example, the concentration, depth of the test drop, amount of reagent added, acidity, etc. These variations are, however, not of a kind to render the test doubtful, long prisms, either singly or in groups being the rule. Even a small amount of cadmium destroys the feathery and...
Page 199 - A number of other methods for the microscopic determination of the refractive indices of liquids have been proposed, but these require specially constructed prisms, wedges or lenses, or fragments of glass of known index of refraction. For information as to methods, apparatus and accuracy the student is referred to the excellent paper by FE Wright, The Measurement of the Refractive Index of a Drop of Liquid. Journal Washington Academy Sciences 4, (1914), 269. Determining Thickness by Displacement...
Page 338 - ... of hexagonal plates. Their color by transmitted light varies from a reddish yellow in very thin plates to reddish brown with a tinge of dirty violet or even deep black as the thickness of the crystal increases. Remarks. — The arsenic acid can be added directly to the test drop to either neutral or to weak nitric acid solutions, but the best and most uniform results seem to follow the procedure suggested above. The amount of ammonium hydroxide added to the reagent drop must never be sufficient...
Page 337 - ... separate have the appearance of hexagonal plates. Their color by transmitted light varies from a reddish yellow in very thin plates to reddish brown with a tinge of dirty violet or even deep black as the thickness of the crystal increases.
Page 290 - ... (d) — Try testing for a trace of Ca in the presence of a large quantity of salts of the elements of Group I.
Page 331 - To the washed precipitate add one or two drops of strong ammonium hydroxide. After a second or two of contact, draw off the ammoniacal solution from any undissolved precipitate. Do not heat the preparation. Allow the preparation to stand. Almost immediately the drop becomes turbid around the edges, because of the separation of minute crystals of silver chloride; these crystals increase slowly in size, but are always very small, requiring a moderately high power for distinguishing their form. From...
Page 326 - Recrystallized in the presence of Group I, double chlorides result, which generally separate more slowly. The crystal form is quite different from that of the normal salt. It is quite important that the student should be familiar with at least the double chloride of cesium and lead (cesium chloroplumbate), since this compound not infrequently makes its appearance when testing for tin with cesium chloride and is quite apt to puzzle the beginner. Alkalies convert lead chloride into a basic chloride...
Page 295 - The crystals of strontium oxalate are similar to those obtained with calcium, but are usually distinctly larger, and crosses, prisms, and four-pointed rosettes are more abundant and larger. The crystals are either tetragonal or monoclinic depending upon whether formed in the cold or separating from hot solutions. Precautions. To avoid error when testing with oxalic acid, it is always advisable, after the crystals have well formed, to draw off the supernatant solution and add dilute sulphuric acid...

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