ON THE LATENT HEAT OF FUSION OF ICE _____
B Y LEO FRANK GUTTMANN
While engaged in some calorimetric determinations I required t o know the latent heat of fusion of ice with some accuracy, and consulted the data given in Landolt and Bornstein's tables. It was surprising to find that the most trustworthy figures, those of Regnault (79.24 calories) and of Bunsen (80,03),differed by nearly I per cent. Aseach of these experimenters could be trusted to work to I part in I ,000, the difference was too great to strike a mean value. After all the papers on the subject had been carefully studied to find a cause for this discrepancy, it appeared that A. W. Smith' had been similarly struck by this fact and been led to redetermine the latent heat of fusion of ice. Smith gives a critical survey of the previous determinations in his paper, but as there is some difference in our conclusions, I will state the results of my investigation. A very careful series of determinations had been made by de la Provostaye and Desains,2 using dry ice at its meltingpoint, and they found 79.25 as the mean of 17 experiments. (Landolt and Bornstein erroneously give 79.01.) Regnault made two sets of experiments,' and found 79.06 using dry solid ice, and 79.21 using pure snow. A considerable quantity .of snow was used, and on account of its finely divided state and subsequent rapid melting in the calorimeter, the duration of each experiment was only from I to I + minutes, The cooling correction was very small and could have produced no sensible error in the results. The snow was always at a teniperature below oo,and could have contained no water. There seems t o be no source of error in this series of measurements, and the value 79.24 should be very accurate. As Smith (2. c.) has already pointed out, ice at its melting-point is sure Physical Review, 17, 193 (1903). Ann. Chim. Phys. [3], 8, 5-19 (1843). Ibid. [j], 8, 19-27 (1843).
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Leo Frank Guttnzann
to contain some water, and the values 79.25 and 79.06 cited above may be dismissed as being too low. But on p. 2 1 of his memoir Regnault states: “La temperture de la glace etait inferieure 2 zPro, mais seulement d’une fraction de degr6, par consequent, la glace, avant de se fondre, absorbait une certaine quantit6 de chaleur pour monter A zPro. La determination de cette quantite exige la connaissance de la capacit6 calorifique de la glace, j’ai admis qu’elle ktait la mkme que celle de l’eau.’’ The specific heat of ice near its melting-point has been determined by Person’ and does not differ sensibly from 0.500. I have therefore recalculated Regnault’s results, using 0.500 for the specific heat of snow, and find the mean value for the latent heat of fusion of ice, as determined from his experiments, t o be 7 9 . 4 1 . ~ Now as to Bunsen’s value: The accuracy of the ice calorimeter has been rather overestimated, but should certainly be I in 1,000. After a careful study of Bunsen’s paper,3 only trifling sources of error could be found. The latent heat of fusion of ice was determined by dropping into the inner tube of the ice calorimeter a small glass tube containing 0.333 gram of water, previously heated to 100’ in a steam jacket. The specific heat of the glass had been determined from only two experiments, but the error thus introduced is negligible. Two consecutive experiments were made, and the results naturally only differed slightly from each other. A greater source of error is introduced by the variation of the density ‘of the ice in the calorimeter. The peculiar alteration in structure which the calorimeter ice Compt. rend., 23, 162 (1846) ; Ann. Chim. Phys. ( 3 ) , 21, 307 and (1847)* I n Ann. Chim. Phys. [3], 30, 80 (1850),Person states that Regnault found 79.43 for the latent heat of fusion of ice, his experiments being corrected for the specific heat of ice, which is taken to be 0.48. H e does not mentioti that lie (Person) applied the correction, and the recalculated value does not appear in Landolt and B6rnsteiu’s tables. Smith, in his paper, mentions that Regnault assumed the specific heat of ice to be equal to that of water, and yet uses the figure 79.24 in taking the mean of previous determinations. Pogg. Ann., 21, 1-31 (1820). 312
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O n the Latent Heat of Fusion of Ice
28 I
undergoes in course of time, has been noticed by all experimenters. It is extremely likely that this change is accompanied by a variation of density, and the values obtained by different observers for the weight of expelled mercury equal to I calorie, vary from 15-44 to 15.57 mg, one experimenter even finding 15.26. Nichols, has fully investigated this subject and concludes that old and new ice differs greatly in density. He obtained 0.91661 for the density of pure ice, and 0.9161 for ice frozen by means of a mixture of CO, and ether, although after twenty-four hours this attained the above value. Bunsen’s value is 0.91685 and differs by 2 in 10,000 from Nichols’, introducing an error of 2 in 1,000 in the amount of ice supposed to have been melted in the calorimeter. Zakrzewski,, using an improved form of Bunsen’s dilatometer, found 0.91660. Nichols moreover found pure natural ice to be denser by I part in 1,000 than calorimeter ice. Barnes3 finds that the difference between the densities of old and new ice may amount to as much as 2 in 1,000, and depends on the age of the ice. As Bunsen used the same mantle of ice in the calorimeter for many weeks, an uncertain and appreciable error is introduced in the value found by him for the latent heat of fusion of ice. The specific heats of various metals determined by Bunsen are throughout lower than the values obtained by Regnault, a fact t o which he himself drew attention. Regnault’s recalculated value 79.41 is therefore the most accurate and trustworthy of the older determinations. One other correction can be applied. Regnault tabulates all his experimental data in full, and on recalculating his figures I obtained the value he gives if the specific heat of the water in the calorimeter is taken to be unity a t :ill temperatures, There is some difficulty in reducing many of Regnault’s experiments to a definite heat unit, on account of the error in his -
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Physical Review, 8, 21-37 (1899). Wied. Ann., 47, 157 (1892).
Physical Review,
13, 55-59
(1901).
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Leo Frank Guttmann
formula for the variation in the specific heat of water at ordinary temperatures. This does not apply in this case, and I was able to reduce his results substituting the values for the specific heat of water given by Griffiths (Thermal Measurement of Energy, Table VII). When this is done, the true mean value for the latent heat of fusion of ice as determined by Regnault is found to be 79.59. The value found by Smith (1. c.) is 334.21 joules = 79.90 mean calories, assuming I Clark (15") = 1.434 volts, and I calorie = 4.1832 joules. The value now generally adopted for I Clark (15') = 1.433 volts, and Smith's value must be decreased in the ratio of (1.433: 1.434). This. is also the correction applied by Professor Kohlrausch. (Private communication to the author.) The value adopted for J has, however, also undergone a change, and the Berlin Congress in 1903 fixed 0.23872 calories as the most probable value (4.1890 joules = I calorie). Recalculating Smith's value for I Clark (15') = 1.433 volts, and 4.1890 joules = I calorie, we get 79.67 calories for the latent heat of fusion of ice. I could find no source of error in Smith's accurate experiments, and have therefore adopted 79.67 as the most accurate value. Regnault's corrected value 79.59 is in good agreement with this, and again shows the skill and accuracy of this classic experimenter . It had been intended to publish this note together with other experimental work, but it has not yet been found possible to' complete all the calculations. The frequency with which Regnault's old value is quoted, for instance see Leduc (Comfit. rend., 142, 46-48, I 906), has necessitated publication. Chemical Department, College City of New York
