Elementary Chemical Microscopy

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John Wiley & sons, Incorporated, 1921 - Chemical microscopy - 479 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 36 - In preparations thus illuminated objects appear to be self-luminous and are therefore bright upon a black background. This method is invaluable for demonstrating the presence of very minute bodies or those whose index of refraction is so very nearly the same as that of the medium in which they occur as to cause them to escape detection when illuminated by transmitted light.
Page 384 - ... 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 383 - Finally many of the crystals which 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 crystals increases.
Page 30 - ... inclined at an angle of forty-five degrees with the elevation of the object ; then it is plain, that since the angle of reflection is equal to the angle of incidence, the greatest part of the rays which fall upon the horizon will...
Page 341 - 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...
Page 373 - KCl; of NH4C1; of CsCl. d. Test a solution of Pb and Sb. Then one of Pb and Bi. Then one containing all three elements. e. To a preparation of PbCl2 add a drop of NH4OH. C. Through the Formation of a Triple Nitrite of Lead, Copper and Potassium. To the moderately concentrated neutral test drop add a trace of acetic acid, then a fragment or two of sodium acetate and of copper acetate. Stir. Then add a fragment of potassium nitrite. There is formed the salt K2CuPb(NO2)6 as tiny squares or rectangular...
Page 372 - 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 389 - Of the above listed alum-forming elements, aluminum is the only one which unites with cesium or rubidium sulphates to form easily crystallizable alums. The other elements unite with these two sulphates only with difficulty, and the alums formed can be regarded, from a microchemical standpoint, as difficultly crystallizable. Sodium, potassium and ammonium sulphates readily unite to form more or less crystallizable alums with the other alum-forming elements as well as with aluminum.
Page 373 - Thallous salts yield with hydrochloric acid star- and cross-like crystallites differing considerably from those given by lead. There is little danger of confusing these two elements, since recrystallizing thallous chloride from hot water, in which it, like lead chloride, is soluble, yields well-formed cubes. In the presence of chlorides of antimony and bismuth complex chlorides of low solubility are sometimes formed, against which the analyst should be on his guard. Silver gives an amorphous precipitate...

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