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then reduced to suit the engraved scales. Thermometer number 741 was of the Jena normal glass; G was of the glass of which Geissler made his thermometers. The boiling point was determined after half an hour of exposure to steam. The freezing point was determined by noting the maximum depressed zero within two or three minutes after the last exposure to steam. The zero point was frequently

b

Eb

redetermined.

Temperatures determined with the two thermometers agreed as closely as different readings of the same thermometer. To the scale of these two thermometers were reduced the readings of the other thermometers used for the temperatures of FIG. 3.-Collar and pan the water in the hydrostatic weighings.

a

for submersion of globes.

DETAILS OF A HYDROSTATIC WEIGHING.

To give a clear idea of the details of the process, part of the determination of the volume of globe No. 1 is here given: first, the observations made on April 7th; secondly, the computation for this day; and, thirdly, the results for each of the other days on which this globe was weighed in water.

HYDROSTATIC WEIGHING, APRIL 7th.

On balance B, Globe 1, cage and pan, weights ABCDEFGHIJ, left.

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In the reduction, the indications of the thermometers at the top and bottom of

One of these was somewhat

They served to show the

the cylinder of water were not included in the mean. above the globe, and the other was somewhat below. presence or absence of thermal inequalities producing currents; the other thermometers fairly showed the temperature of the water in which the globe was floating.

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In the same way, we get for the other weights and temperatures given above,

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These determinations are recorded as one result: all the results for this globe are given in the table of data concerning the capacity of globes.

HYDROSTATIC WEIGHING OF THE LARGER GLOBES.

In the case of the larger globes, the manipulation in the hydrostatic weighings was slightly different; the cylinder filled with water in which the globe was immersed was too heavy to be conveniently moved into and out of the case on which the balance had been placed. The cylinder for the larger globes was accordingly placed permanently in a closet about three metres square which was built inside a basement room of tolerably constant temperature. It was surrounded with a non-conducting case. Over it was placed the balance with a clear space of three quarters of a metre beneath it. Further, the volume of water needed was now so much that the removal of it every time a globe was immersed became tedious. So a triangular platform was attached to three brass rods, and these to cords passing over pulleys in the ceiling, so that the platform with any load could be raised or lowered at will. The cords were arranged to pass before, behind, and to the left of, the balance without interfering with it. This platform being raised, the pan and its weights were arranged and the globe and its collar were attached to it. The platform was then lowered, and the globe sank to the bottom. The latter was then raised a little and suspended by a wire from the balance, and weighed as

before.

In the other method, the water was stirred by pouring, which was tedious.

With the present apparatus, alternate raising and lowering of the globe by means of the movable platform soon made the temperature uniform.

When the thermometers were used for several weeks in the horizontal position, the column of mercury in two of them sometimes separated, so that they could no longer be read. For some determinations, therefore, I procured thermometers divided into fiftieths of a degree, having the graduations at the end of a long tube. With these the temperature could be read, even at the bottom of the cylinder, with the thermometer in the vertical position. By moving them, the temperature of the water at all depths could be determined.

Most determinations were made at the temperature of the room. But a few determinations were made with the temperature below 4° C., some by using ice in a large tank, and some by working in an attic room in winter,

6.-EXPANSION OF WATER AND OF GLASS.

The volume of one gramme of water at different temperatures which is required in reduction of the hydrostatic weighings was taken from the results of Marek, Thiesen, Scheel, and Kreitling, as given in the Beiblaetter zu den Annalen, 18, 59. The following table gives the volume of one gramme of water for each tenth of a degree from 0° to 22°:

VOLUME OF ONE GRAMME OF WATER AT TEMPERATURE T.

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The coefficient of expansion of the glass globes used for weighing oxygen was determined by making three weight thermometers of the necks of three globes,

which were filled with mercury by boiling in a vacuum.

These were transferred

from ice to steam, and the expansion calculated from the amount of mercury expelled at the latter temperature. The height of the barometer during the exposure to steam, corrected for the force of gravity at my laboratory, was 744.1 millimetres. Hence the temperature of the steam, according to the table by Broch,* was 99.41°. The observations were as follows:

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At o°, Log. 1.133 3888, at 99.41°, Log. 1.125 5573, the cubic expansion of the glass between 。° and 99.41° is found

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Each globe was weighed in the air while open, and the apparent weight cor rected for the weight of the air displaced by the glass and by the weights. It was then immersed in water, filled, and weighed, using the same cylinder and the same thermometers as in the previous hydrostatic weighings. The solid contents of the globes were then computed with the values of the expansions of water and glass just mentioned. As an example of the process, the determination of the solid contents of globe No. 1 is given.

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If now we subtract the solid contents of each globe from the volume we shall have its capacity. For instance, we have

* Travaux et Mémoires du Bureau International, 1 A, 46.

The glass was the ordinary soft German glass, obtained from C. Gerhardt, Marquart's Lager Chemischen Utensilien, Bonn.

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The capacities of the globes used in determining the density of oxygen are given in the following table:

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The following table gives all the hydrostatic weighings of these globes with the corresponding temperatures. All the weights are corrected for the weight of air displaced by them, and the weights which were used in water are corrected for the expansion of water and of brass to the temperature of the water in which they were immersed. These corrections are not very large, and may be assumed to be sufficiently well determined. If the other reductions need subsequent correction, the data given are sufficient.

It is, of course, obvious that my determinations of the capacity of a globe are not as accurate as they might have been made. By weighing the water contained in a globe at the temperature of melting ice, Regnault determined the capacities of the globes used by him in weighing known volumes of gases with a mean error of one fortieth of a cubic centimetre.* But it is thought that the accuracy attained is all that is necessary, especially since it is much more than that of other processes on which the knowledge of the density of a gas depends.

DATA CONCERNING THE CAPACITY OF GLOBES.

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* Mendeleef, Annals of the Bureau of Weights and Measures, St. Petersburg, Part I., 59.

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