Helping San Diego, California and beyond since 1997.
Do you need
volunteer, community service, work, military or court hours?
|
|
Helping San Diego, California and beyond since 1997.
|
|
Click here and add this page to your favorites!
|
Encyclopedia Britannica - Main :: SOU-STE |
|
|
SPECIFIC HEAT OF MERCURY BY CONTINUOUS ELECTRIC METHOD Flow of Hg. Rise of Temp. Watts. Heat-loss. Specific Heat. gm./sec. do EC MO Per gm. deg. 8.753 11.764 14.862 0.655 .13780 joules 4'594 12.301 7.912 0.685 .03297 cals. It is assumed as a first approximation that the heat-loss is proportional to the rise of temperature do, provided that do is nearly the same in both cases, and that the distribution of temperature in the apparatus is the same for the same rise of temperature whatever the flow of liquid: The result calculated on these assumptions is given in the last column in joules, and also in calories of 2o C. The heat-loss in this example is large, nearly 4'5 % of the total supply , owing to the small flow and the large rise of temperature, but this correction was greatly reduced in.subsequent observations on the specific heat of water by the same method. In the case of mercury the liquid itself can be utilized to conduct the electric current. In the case of water or other liquids it is necessary to employ a platinum wire stretched along the tube as heating
II s= 1 +0.0O0O4t+0.0000009t2 ( Regnault
formula
formula
Regnault
S =Sloo +.00023 (t-100) (Bosscha-Regnault) (4). Me he work
work
thermometry and to the reduction of the results to the absolute scale of temperature. The agreement of his corrected results with those of Griffiths by a very different method, left very little doubt with regard to the rate of diminution of the specific heat of water at 20 C. The work of A. Bartoli and E. Stracciati by the method of mixture between 0 and 3o C., though their curve is otherwise similar to Rowland's, had appeared to indicate a minimum at 2o C., followed by a rapid rise. This lowering of the minimum was probably due to some constant errors inherent in their method of experiment. The more recent
great
thermometry , and the discrepancies of individual measurements at any one point nowhere exceed 0.3 %, but he did not vary the conditions of the experiments materially, and it does not appear that the well-known constant errors of the method could have been completely eliminated by the devices which he adopted. The rapid rise from 25 to 750 may be due to radiation error from the hot water supply , and the subsequent fall of the curve to the inevitable loss of heat by evaporation of the boiling water on its way to the calorimeter. It must be observed, however, that there is another grave difficulty in the accurate determination of the specific heat of water near too C. by this method, namely, that the quantity actually observed is not the specific heat at the higher temperature t, but the mean specific heat over the range 18 to t. The specific heat itself can be deduced only by differentiating the curve of observation, which greatly increases the uncertainty. The peculiar advantage of the electric method of Callendar and Barnes, already referred to, is that the specific heat itself is determined over a range of 8 to to at each point, by adding accurately measured quantities of heat to the water at the desired temperature in an isothermal enclosure, under perfectly steady conditions, without any possibility of evaporation or loss of heat in transference. These experiments, which have been extended by Barnes over the whole range o to too, agree very well with Rowland and Griffiths in the rate of variation at 20 C., but show a rather flat minimum of specificheat in the neighbourhood of 38 to 40 C. At higher points the rate of variation is very similar to that of Regnault's curve, but taking the specific heat at 20 as the standard of reference, the actual values are nearly 0.56% less than Regnault's. It appears probable that his values for higher temperatures may be adopted with this reduction, which is further confirmed by the results of Reynolds and Moorby, and by those of Ludin. According to the electric method, the whole range of variation of the specific heat between to and 80 is only 0.5 %. Comparatively simple formulae, therefore, suffice for its expression to 1 in 10,000, which is beyond the limits of accuracy of the observations. It is more convenient in practice to use a few simple formulae, than to attempt to represent the whole range by a single complicated expression:-Below 20 C. s=0.9982+0.000,0045 (t-4o)2-o.000,0005 (t-20)3. From 20 to 6o, s- 0.9982+0000,0045 (t-40)2 (5). ((s=0 9944 I 000 o4t~ o000,000y tz (Regnault Above 6o to 2000 j corrd.) (( s= 1.000+0.000,22 (t-6o), (Bosscha corrd.) The addition of the cubic term
change near the freezing-point. This effect is probably due, as suggested by Rowland, to the presence of a certain proportion of ice molecules in the liquid, which is also no doubt the cause of the anomalous expansion. Above 6o C. Regnault's formula is adopted, the absolute values being simply diminished by a constant quantity 0.0056 to allow for the probable errors of his thermometry. Above too C., and for approximate work generally, the simpler formula of Bosscha, similarly corrected, is probably adequate.The following table of values, calculated from these formulae, is taken from the Brit. Assoc. Report, 1849, with a slight modification End of Article: SPECIFIC HEAT OF MERCURY BY CONTINUOUS ELECTRIC If you wish, you can link directly to this article.
<a href="http://jcsm.org/StudyCenter/Encyclopedia/SOU_STE/SPECIFIC_HEAT_OF_MERCURY_BY_CO.html"> SPECIFIC HEAT OF MERCURY BY CONTINUOUS ELECTRIC </a> |
|
|
(Previous) SPECIES |
(Next) SPECIFIC HEAT OF WATER IN TERMS OF UNIT AT 200 C |
|
Sponsored Advertisements