Organic 2 Review Problem 447

Organic 2 Review Problem 447 - few degrees. The Tabloid or...

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QUANTITATIVE ANALYSIS 43* the bulb to the whole of the reservoir-mercury collected at a, and then to cool or warm the bulb until the reservoir-mercury reads the required temperature on the small scale D. The mercury thread is then broken at a, and at the desired temperature, the thermometer will then read o° on the major scale S. When actually taking a reading on the scale S during an experiment, a small lens is used, and the usual precautions must be taken to avoid an error by "parallax." It is always advisable to use a particular Beckmann thermometer either solely for freezing-point determinations or solely for boiling-point determina- tions. If a thermometer which has been used at low temperatures for some time is reset for boiling-point determinations, it will be found that the glass bulb of the thermometer (as distinct from the mercury) does not adjust itself at once to the higher temperature: a slow "settling-down" process occurs, during which the reading of the thermometer steadily changes. This effect is of course negligible when the thermometer is reset over a range of only a
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Unformatted text preview: few degrees. The Tabloid or Pellet Press. When determining the molecular weight of a solid substance in solution, it is often most convenient to add a weighed pellet or tabloid of the substance to the solvent. A tabloid press is therefore used to compress the powdered substance into a pellet of suitable weight. The press consists essentially of a cylinder C (Fig. 78), having a circular bore through its long axis. The cylinder C fits over a metal base B, and a plunger P fits closely into the circular bore: the plunger P and the cylinder C have side-arms to limit rotation in the frame F. FIG. 78. In use, the cylinder C is fitted over the base B, and the powdered compound is placed in C in small quantities at a time, and pressed firmly down (by hand) with the plunger P. When sufficient material has been placed in C, the whole unit is fitted into the frame F as shown, and the screw-plunger S screwed down...
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