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In the above experiments it will be noticed that the results obtained from mercury increased at each fresh attempt, and this was due to successive improvements in the method of preventing loss of heat. In experiment A, owing to want of practice, several seconds were wasted in pouring the hot mercury into the receiving tube; in B, this was done much more expeditiously; for D, the cork collar was introduced into the mouth of the receiving tube, thus preventing loss of heat by contact with the cold iron; while in E, a larger quantity of mercury was heated to 65° C. instead of to nearly 100° C., the cork collar being retained, thus the loss of heat was still further reduced.

In all these experiments however the mercury had to flow over the cooler parts of the inner test tube, of which about two inches towards the mouth were not exposed to the steam of the hypsometer, being surrounded by cork and the string used in fixing the three tubes firmly together; and thus owing to the large extent of the surfaces in contact, the glass must have cooled the mercury appreciably. The platinum experiments agree fairly well together, and it is easy to see that the loss of heat must be less than for the mercury, for the solid platinum would shoot more rapidly out of the test tube into the receiving tube, and further, the surface in contact with the cooler parts of the test tube while passing out would be much less than in the case of a liquid like mercury; evidently also the cork collar would be less necessary for the platinum; it was used in F and G but not in C, which gives a result very nearly the mean between F and G.

Attempts were also made to estimate the temperature of copper and platinum heated in the Bunsen flame by means of this calorimeter. To do this a piece of platinum or copper wire was coiled up and placed on a support about 12 inches above the mouth of the receiving tube; through this coil a piece of fine platinum wire was passed leading vertically down to the receiving tube, in which its lower end was kept by means of a platinum weight. A screen was placed below the little coil, and the Bunsen flame was allowed to play on it until it was at a steady white heat; the screen was then removed, the cork

withdrawn from the receiving tube, and the coil was pushed off its support, and being guided by the fine wire it fell right into the receiving tube, and the cork was replaced. In the first and third of the following experiments some time was lost in replacing the cork, and thus they both give a lower result than the second, and as this cause of error was about the same in both these cases they agree fairly together.

1ST EXPERIMENT.-Platinum used. Weight of platinum 3.502 grammes. Final temperature of calorimeter 15°.2 C.

1.345 scale divisions correspond to 1 heat unit.

This number is the mean of the three previous experiments on platinum.

0.0373 = specific heat of platinum from 0° to 1000° C.

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Then (T-15°2) = fall in temperature of Platinum

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2ND EXPERIMENT.-Platinum used. Final temperature of calorimeter 15°-5 C. Other numbers as before.

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3RD EXPERIMENT.-Copper used. Final temperature of calorimeter, 15°7 C. Weight of copper, 1.186 grammes. Specific heat taken as 0·100,

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No. 15. CLÉMENT AND DÉSORMES' EXPERIMENT

ON THE SPECIFIC HEATS OF GASES.

A LARGE number of observations have from time to time been taken with a simple arrangement of Clément and Désormes❜ experiment. A large globe about twelve inches in diameter has its neck connected with a wide three-way tube, one opening leading to a sulphuric acid pressure-gauge, and the other connected by wide india-rubber tubing with a piece of wide glass tubing. For the compression experiments the glass tubing dips under mercury, and the sudden communication between inside and outside is established by simply lifting up the tube; while for the rarefaction experiments the india-rubber tube is closed by an iron bar buttoned down, and the communication can be made by releasing the button and lifting up the bar.

To minimise the loss of heat by radiation a small quantity of strong sulphuric acid is introduced into the globe, and the air which entered had always to pass through a large flask filled with very coarse lumps of fused calcium chloride.

The experiments shew that it only requires a little practice to be able to get any desired result with the apparatus, for if the communication is established for too short a time the result gives too great a ratio, while if the time be too long the result is too small. It seems not to be possible to re-arrange the apparatus in any simple way to ensure automatically that the opening shall be sufficiently long for the pressure to be equalised and no longer, and this point becomes therefore to some extent a matter of conscience with the observer. The results obtained point to 1:33 as the value of the ratio of the specific heats to be obtained from this apparatus.

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