A text-book on chemistry : for the use of schools and colleges / by John William Draper.

  • Draper, John William, 1811-1882.
Date:
1846
Catalogue details

Licence: Public Domain Mark

Credit: A text-book on chemistry : for the use of schools and colleges / by John William Draper. Source: Wellcome Collection.

Provider: This material has been provided by the National Library of Medicine (U.S.), through the Medical Heritage Library. The original may be consulted at the National Library of Medicine (U.S.)

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    dex. To understand the action of this instrument, it is only necessary to consider what will take place when it is carried into a room the temperature of which is very high or very low. If the former, the air in hoth bulbs, becom- ing equally warm, will expand in both equally, and the column of fluid which acts as an index being pressed equally in opposite directions, does not move at all. If the latter, the air in both bulbs cooling equally, contracts equally, and again no movement ensues. It is immateri- al, therefore, whether we warm or cool both bulbs, the instrument is motionless. But if one of the bulbs, c, is made warmer than the other, d, movement at once ensues in the liquid column from c toward d. Movement of the index, therefore, takes ])lace when the bulbs are at differ- ent temperatures, and hence the instrument is called a differential thermometer. It was formerly of considera- ble use in researches connected with radiant heat. Different liquids expand different- ly for the same thermometric dis- turbance. This is easily shown by an apparatus, as Fig. 12, in which we have three tubes, a, h, c, with bulbs on their ends, dipping into a trough, f, of tin plate. The tubes and bulbs should be all of the same size, and filled with the liquids to be ti-ied to the same height. To each a scale is annexed. Let a be filled with quicksilver, b with water, and c with alcohol; on pouring hot water into the trough, two phe- nomena are witnessed: 1st. All the liquids expand; 2d. They expand unequally when compared together, the mercury expanding least, the water intermediately, and the alcohol most. Unlike gases, all liquids expand irregularly as their temperature rises, a given amount of heat producing a much greater effect at a high than at a low temperature. Ten degrees of heat, applied to a given liquid at 200°, will produce a greater expansion than if applied at 100°. The reason appears to be, that as a liquid dilates its co- If this instrument be carried into a warm and then into a cold room does its index move ? Why is it called differential thermometer ? How can it be shown that different liquids expand differently ? Of mercury water, and alcohol, what is the order of expansion ? Do'liquids like tra's' es, expand with regularity ? What is the cause of the difference ?