Air thermometer

In such an osmometer the lateral walls on the depth of the half cells are made up of perforated brass plates the width and the depth of each groove in the plate are 1.5 mm and the distance between two adjacent groove is also 1.5 mm. The diameter of osmometer cell is 11.5 cm. The semi-permeable membrane is clamped between the two half-cells. The solution is placed in the glass-tube having a needle-type stopcock and is fitted with pure solvent. The volume of the osmometer cell is about 7 ml. The assembled osmometer is put in a double-walled air thermometer. The temperature fluctuations in the thermostate are 0.05°C. 

A tabular statement of the rate of expansion of a few of the metals Is subjoined, with a comparative view of the results when the temperature is measured with the air thermometer, and with one constructed of the metals under experiment —... 

Although there is no record that he ever calibrated the tube, he used it in temperature study. Galileo s thermometer was impossible to calibrate even if he had decided on fixed points with which to establish specific temperatures because it was exposed to the atmosphere and subject to variations in atmospheric pressure. By 1640, it was realized that the air thermometer was subject to variations of barometric pressure and the sealed thermometer was created. However, the need to establish fixed points of reference had still not been addressed. 

In the experiments of Meyer and Munch the mixture of combustible gases and air (or oxygen) was passed through a capillary tube to the base of a small glass vessel, in which the lgmtion was destined to take place, and which was inserted in the bulb of an air thermometer. When the mixture inflamed, the temperature of the gases was calculated from the volume of the gas m the air thermometer. 

Guthrie used a diathermometer, consisting of two hollow brass cones with the apices in opposite directions, the liquid being in a thin film between the bases. The upper cone was filled with hot water, and the lower served as the bulb of an air thermometer the results were worthless. 

Starkweather pointed out that Regnault s temperature scale was that of the air thermometer, and by reducing his results to 15° g.cal. on this scale, he found ... 

The gas thermometer was discovered by Galileo. Liquid thermometers were introduced later. Fig. 1 is a diagram of Gahleo s air thermometer, Fig. 2 of a liquid thermometer as used at the present day. 

Johann Heinrich Lambert (1728-1777), mathematician, physicist and philosopher, was a tutor for the Earl P. v. Salis in Chur from 1748-1759, where he wrote his famous work on photometry [5.2]. In 1759 he became a member of the Bavarian Academy of Science and upon proposal by L. Euler became a member of the Berlin Academy of Science in 1765. Lambert wrote several philosophical works and dealt with subjects from all areas of physics and astronomy in his numerous publications. He presented the absolute zero point as a limit in the expansion of gases and constructed several air thermometers. In 1761 he proved that v and e are not rational numbers. His works on trigonometry were particularly important for the theory of map construction. 

The former case is realized in nature in the expansion of ideal gases and the mixture of dilute solutions the most important temperature measuring instrument, the air thermometer, depends upon this fact. 

In addition, a number of measurements were made with an air thermometer, the details of which will not, however, be here described. 

Column heating jackets by thermocouples, contact thermometers or air thermometers (sections 7.7, 8.2.1, 8.2.2) ... 

In batch distillation the column temperature increases during the course of the operation, frequently by sudden increments the adjustment of the jacket temperatures by hand is consequently a matter of some difficulty. As the result of temperature lag, differences up to 30 deg. C between the jacket and column may occur, but these differences may be reduced considerably by automatic control. For this purpose air thermometers, thermocouples or resistance thermometers can be employed as sensing devices. Thermocouples are placed at the top and bottom of the column these together act on-the coil of a galvanometer, the position of which is sensed at short intervals by an electric switching device. The latter opens or closes the circuit... 

Gay-Lussac invented a portable barometer, a steam injector pump, a maximum and minimum thermometer for use in the sea, a modified Volta s eudiometer, and an air thermometer and a spirit blow-lamp. He adapted an ordinary furnace for use as a muffle furnace and described a new method of heating with charcoal impregnated with sodium carbonate. 

A modification of Dumas vapour density method was used by Mitscherlich, who measured higher temperatures (270°-700°) with an air thermometer, the cylindrical glass tube containing the substance being put inside an iron tube heated in a charcoal furnace. For 300" a metal bath was used. He determined the vapour densities of bromine, sulphur, phosphorus, arsenic, mercury, sulphur trioxide, phosphorus pentachloride, antimony pentachloride, calomel and other mercury salts, and arsenious oxide. Sodium and potassium vapours attacked glass. He used H2 = i as unit with H = i the number of atoms in an equal volume found were i for mercury, 2 for bromine, 6 for sulphur, 4 for phosphorus and arsenic. The densities of phosphorus pentachloride and of antimony pentachloride were half the normal values. Mitscherlich did not appreciate the consequences of Avogadro s hypothesis e.g. he says i vol. of... 

Le Fevre describes and figures chemical furnaces and apparatus, including an air-thermometer with two bulbs and a water-index, for measuring temperatures and also shows a lamp furnace with an oil lamp (which could have one or more wicks of different sizes) adjustable by a screw. ... 

In 1755 Cullen read to the Edinburgh Philosophical Society an essay Of the Cold produced by evaporating Fluids, and of some other means of producing Cold . In this he describes the lowering of temperature produced by the evaporation of a volatile liquid under the receiver of an air pump, and by the sudden (adiabatic) expansion of air. He froze water in a vessel in which was immersed another vessel containing nitrous ether evaporating rapidly in an exhausted receiver, using an air thermometer in these experiments. In this work, Cullen was assisted by Matthew Dobson of Liverpool and afterwards of Bathi ... 

Calibration.—The thermometer must be carefully calibrated, and it would be a great advantage if all thermometers were compared with an air thermometer, for two mercurial thermometers, constructed of different varieties of glass, even if correct at 0° and 100", will give different and incorrect readings at other temperatures, more especially at high ones, for various reasons ... 

Assuming that the liquid is pure, that the thermometer has been compared with an air thermometer, and that the precautions mentioned in the last chapter have been attended to, the corrected temperature will give the true boiling point of the liquid under a pressure equal to that of the atmosphere at the time. It is frequently necessary, however, to compare the boiling point of the liquid with that observed by another experimenter, or to compare it... 

When steam is heated idone, it expands according to the law previoosly given for permanent gases but when water is present, and the experiment is performed in a closed vessel, the elastic force of die steam increases in a far mora rapid ratio thandminorease of temperatare. The following table gives the tension of aqueous vapour, as determined by experiment at different temperatures measured on the air thermometer. 

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