Scooling in sheet-iron cylinders of different thicknesses. The standard-piece at the time weighed 6000 grains Troy, and its temperature at the commencement of every experiment was 212°.

After the preliminary series already given, (Tab. IV.) two other sets of experiments were made, one in each of two glass vessels similar to that in which the preceeding trials had taken place,-equal to each other in liquid capacity, but of different thicknesses; the one being more than four times as heavy as the other. Table V. contains the experiments with the thicker, and table VI., those with the thinner of these vessels. The particular object of these trials was to determine, if possible, the effect of the containing vessel on the general result of the experiment; in other words, to decide its specific heat, by observing the difference which would arise from a mere change of thickness in the containing vessel, while all other circumstances of the trial were the same, in both cases. A comparison of several experiments in each table, with corresponding ones in the other, will show that when the water at the commencement was from 60° to 63.5°, the actual difference in the rise of temperature, due to a difference in the weight of the containing vessels of (12272-2996)-9276 grains of glass, was about three tenths of a degree; and from the comparison of nine experiments in the first of these tables, with the same number in the second, it will be seen that we obtain for the specific heat of glass .111063.* A part of the trials in these and the subsequent series were made by means of the spirit thermometer C, the equivalent of which was only approximately found, on account of not having taken the precaution to weigh the bulb and tube separately before filling the instrument. It is, also, like all other spirit thermometers, liable to some uncertainty in its indications owing to the different quantities of the liquid which may at different times be taken up in wetting the tube,—an uncertainty, which is the greater, the more sudden are the changes to which we submit the instrument.

The equivalent value assigned to it by finding the weight and capacity of an equal length of the same tube is 117.4 grains of water, as hereafter mentioned.

The next apparatus used in this part of the investigation consisted of two glass jars, smaller than those above described, both of the same capacity, but differing from each other in weight, being nearly in the proportion of 3 to 1. The experiments in these two vessels were made in two sets of 6 each, three of each set being commenced in the thicker vessels at a temperature of 60°, and three at 60.5°; and the same number at the same two points in the thinner. The results are contained in table VII., where it will be perceived that from five comparisons between the trials in these two jars the influence of the glass is such as to indicate a mean specific heat of .103086, which taken with the above result of the 9 comparisons

*The principle of calculation applied to all these comparisons is embraced in

the formula x= (T't—Tt'). (w+e.), where x is the specific heat of the container;

Tt'g-T'tg

T' is the gain of temperature by the water when the thinner glass is used; T the gain when the thicker vessel is employed; t', is the loss of temperature by the iron when the thinner, and t, that when the thicker is employed; w, is the weight of water in both cases, and e the equivalent in grains of water, of the liquid in the thermometer; g is the weight of the thicker jar; g' that of the thinner. Thus comparing the two identical experiments 7 and 8, table V., with experiment 6, table VI. in which the initial temperature of the water, and other circumstances, coincided with the former, we have T=5°.76; t=143°.1; T=5°.4; t' = 142°.74; w= 16494.5 grs.; e=152.7 grs.; g = 12. 706 grs., and g = 34.30 grs. Hence T't =824.256; Tt'=770.796; T't-Tt= 54.46; w+e=16.647.2; Ttg = 9793733.976; T'tg = 2827198.08; from which x.130156 the specific heat of the glass by this comparison.

between tables V. and VI., gives a mean specific heat of flint glass of .107074.

As we are now only referring to the apparatus employed, we shall reserve our remarks on the results presented by these tables, respecting the specific heat of iron, until we have described the other methods of verifying

their correctness.

The fourth set of apparatus for this purpose, consisted of two cylindrical copper vessels, of the same height as the glass ones already described: but of such diameter as to contain about 38600 grains, or a little over 5 pounds avoirdupoise of water, and so differing in thickness, that the one weighed nearly 4 times as much as the other. The mode of conducting experiments in these two vessels, and the principle of calculation applicable to them, is entirely similar to that already given for the two pairs of glass jars,except that the equivalent of the glass in the thermometer, was now separately computed.

The results will be found in table VIII., in which it will be perceived that the number of comparisons furnishing data for determining the specific heat of copper, is but two, and of these only one can be considered entirely unexceptionable.

From this it should seem that the specific heat of copper is .10431, whereas the four determinations of Wilke, Crawford, Dalton and Petit and Dulong give .10750 for the specific heat of that metal.

A fifth mode of determining the specific heat of iron was by employing as water vessels two cylindrical sheet iron jars of the same capacity, but of thicknesses differing from each other in about the proportion of 3 to 1. As in the preceding sets, the specific heat of the container may here be found by comparing together experiments made at the same temperature, in the two vessels; and this ought to give their variation, if any exist, from the specific heat of the standard piece itself. Another method is to assume that the specific heat of the standard piece and of the sheet iron containers is the same. The use of the two containers in this latter case serves only to verify each others results, since each furnishes a separate and independent calculation.

The results of experiments in the two iron vessels will be found in table IX. A comparison furnished by two experiments in each vessel, gives by calculation on the principle used in the case of the glass containers the specific heat of the Russian sheet iron, of which they are composed.101714.

Results of Experiments on Specific Heats.

When it is considered that numerous causes interfere with the operations on specific heats, it cannot be cxpected that one, or a few trials, should be deemed sufficient to settle so difficult and intricate a question. For this reason the committee preferred the method of multiplying and varying the trials, and making a deduction from the mean results, in order to verify the general efficacy of the standard piece, in producing vapour.

1. The first part of the preliminary series (table IV.) indicates the effect of radiation from surrounding objects in the apartment to the water

* The formula in this case gives the specific heat of iron z=

is the temperature gained by the water, w= the weght of water in grains, e=the equivalent of the thermometer in grains of water; t = the temperature lost by the standard piece; i=the weight of the standard piece in grains, and 'the weight of the sheet iron containg vessel. See Am. Jour. of Sci. Vol. 27, p. 277.

vessel. The 13 experiments constituting this part of the table, exhibit a mean result of .123004 as the specific heat of iron.

2. The second part of the same series in which the cylinder B. was employed, indicates a decided effect from that precaution, and gives as a mean result.11294, for the specific heat.

3. Experiments No. 16, 20, 23, 25 and 26, the greatest number of comparable results in this part of the series, (differing only in the fourth place of decimals,) gives a mean of .11346.

4. In table V., where the thicker of the two glass cylinders of the same capacity was used, we have the mean result of the whole 14 experiments

.11288.

5. The four experiments No. 2, 5, 6, and 9, which are the greatest number that conform to the third place, give a mean result of .11349.

6. The 10 experiments in table VI., made in the thin cylinder of the same capacity as the foregoing, give the specific heat =.11308.

7. Experiments No. 2, 5, 6 and 7, the greatest number of those which may be regarded as conformable to the third place of decimals, give a mean of .11361.

8. Table VII. contains 3 experiments made in each of the two vessels used in that series, which were performed under a cone of tinned iron to defend the water vessel from radiated heat, but as it was set loosely on the table which supported the container, it did not prevent the motion of air around the latter, and as the experiments made in this manner terminated from three to four degrees above the temperature of the room, there is reason to suppose that the results of those 6 experiments are all below the truth. Taking then the other six of this table, which were made with the same precautions as those in table V. and VI., we have as the mean result in the thicker glass .112952; and that in the thinner .113631.

9. The two experiments which conform entirely with each other, for the thicker vessel, give the specific heat .113498, and the two for the thinner .113489.

10. The mean of all the results, including both those obtained with the cone, and those with the cylinder of tinned iron, to defend the water vessel, give a mean result of .112350, and the six rejected experiments taken by themselves .111511.

11. In the thinner copper vessel, the trials as recorded in table VIII, exhibit the mean of seven results equal to .115752

12. Rejecting those which began and ended too low, and hence gained heat from the air, as well as from the iron, we have in the thinner vessel .112577 as the mean of four experiments which are considered comparable. 13. In the same table eleven experiments in the thicker vessel indicate a a mean of .114990.

14. With the same jar, seven experiments which are considered comparable, give a result equal to .113261.

15. In the thick sheet iron cylinder, weighing 5167 grains, we find by table IX., that the mean of five trials gave a result = .113953.

16. In the same vessel, three experiments which differ only in the 4th place of decimals give a mean specific heat=.113622.

17. In the thinner sheet iron jar weighing 1733 grains, nine trials gave a mean result of .112972.

18. Three experiments in this vessel which differ only in the fourth place of decimals, give a mean of .113365.

The following table embraces a synoptical view of the experiments on specific heat thus far detailed.