60S 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. [January 28, 1871. 
maximum temperature, tlic whole correction required 
was for cooling. The first temperature was read one 
minute after the addition of the acid to the alkaline 
solution, the mixture being- stirred during the whole of 
that time. If 5 represents the correction, and e the ex¬ 
cess of temperature above the air in Centigrade degrees, 
the value of 5 will be given by the following expres¬ 
sion :— 
5 — e X 0-012°. 
As a proof of the accuracy of the method of mixture 
adopted in this inquiry, I may mention that, being de¬ 
sirous to know whether the dilute acids employed in 
these experiments produced any change of temperature 
when mixed with water, I made the experiment with 
nitric acid by the ’method just described, substituting 
water for the alkaline solution, with the unexpected re¬ 
sult of a fall of 0-01°. On varying the conditions of the 
observation, so as to obtain a larger effect, it was ascer¬ 
tained not only that a diminution of temperature had 
actually occurred, but that the observed fall represented 
approximately its true amount. When hydrochloric 
acid of equivalent strength was diluted to the same ex¬ 
tent, an elevation of temperature of 0-05° was produced. 
The accuracy of experiments of this kind, where the 
whole thermal effect observed amounts only to 2° or 3°, 
depends greatly on the thermometer employed. Unless 
its indications are perfectly trustworthy in every part of 
the scale, the labour of the inquirer will only end in 
disappointment. I have therefore taken every precau¬ 
tion to secure this important object. The tube of the 
thermometer was calibrated and divided with care, ac - 
cording to an arbitrary scale, by means of a dividing- 
instrument contrived for the purpose, and provided with 
a short screw of great accuracy made by Troughton and 
Simms. The divisions, etched finely on the glass, cor¬ 
respond to about 0-05° C., and the readings could be 
made with certainty to less than 0 - 01°. The division of 
the scale, corresponding to 0°, was determined from time 
to time in the usual way; and another point, about 
30° C., was fixed by comparison with four other ther¬ 
mometers similarly constructed, whose scales extended 
from the freezing to the boiling-point of water. The 
readings of these four instruments, when reduced to 
degrees, rarely differed from each other within the limits 
to which they could be read, or 0-02°. The reservoir of 
the thermometer used in these experiments -was 75 milli¬ 
metres long, and, when immersed in the liquid, occupied 
nearly its entire depth. 
As some uncertainty always exists -with regard to the 
thermal equivalent of glass vessels, I made tw*o sets of 
comparative experiments—one with a thickly-varnished 
copper vessel, and the other with a vessel of platinum. 
The mean result of these experiments coincided almost 
exactly with the result obtained when the glass vessel 
was employed. 
The weight of the glass vessel which contained the 
alkaline solution was 58 grammes, and corresponded 
thermally to 11-4 grammes of the solutions formed. The 
thermal equivalent of the reservoir of the thermometer 
and of the stirrer was 0-9 gramme. The alkaline solu¬ 
tion weighed 160 grammes, and contained the equivalent 
of 1-738 gramme of S0 3 . The acid solution weighed 
42-5 grammes. Hence the entire thermal value of the 
apparatus, in terms of the solution formed was 
Solution. 202-5 
Glass vessel.11-4 
Thermometer and stirrer. . 0-9 
214*8 grammes. 
A correction (additive) of Jy -was made to the direct 
readings for the mercury in the stem of the thermo¬ 
meter. The results are given to thousandths of a de¬ 
gree, but this apparent minuteness is due to the reduc¬ 
tion of the indications of the arbitrary scale to degrees. 
The following table gives the mean results of the new 
experiments, the acids being arranged in the order of 
their thermal action:— 
Acid. 
Potash. 
Soda. 
Ammonia. 
Sulphuric acid . . 
. 3-378° 
3-353° 
2-976° 
Oxalic acid . . . 
. 3*058° 
3-040° 
2-648° 
Hydrochloric acid . 
. 3-021° 
2-982° 
2-623° 
Nitric acid . . . 
. 2*993° 
2*929° 
2*566° 
Acetic acid . . . 
. 2-852° 
2*832° 
2-492° 
Tartaric acid . . 
. 2-732° 
2*710° 
2*376° 
It is interesting to observe how closely the results in 
the three vertical columns agree relatively with one 
another. The acids follow in the same order under each 
base, and even the differences in the amount of heat dis¬ 
engaged by the several acids in combining with the dif¬ 
ferent bases approximate in many cases closely to one 
another. Thus the heat given out when sulphuric acid 
combines with potash exceeds that given out when 
oxalic acid combines with the same base by 0-320°, the 
corresponding differences in the case of soda and am¬ 
monia being 0-313° and 0*328°. If, in like manner, we 
compare the differences between the heat disengaged by 
the acetic and tartaric acids, we fall upon the numbers 
0-120°, 0-122°, and 0*116°. Even in the case of oxalic, 
hydrochloric and nitric acids, which disengage so nearly 
the same amount of heat, the same order is observed with 
the three bases. It must bo particularly remarked that the 
o^ilic acid disengages from 0-022° to 0-058° more heat in 
combining with these bases than the hydrochloric acid, 
and from 0 - 065° to 0-111° more than the nitric acid. 
The conclusion of MM. Favre and Silbermann, that 
the organic acids (oxalic, formic, acetic, etc.) disengage 
sensibly less heat than the mineral acids, is thus entirely 
disproved; and the original results recorded in my work 
of 1841, according to which oxalic acid disengages at 
least as much heat as nitric, phosphoric, arsenic, hydro¬ 
chloric, hydriodic, boracic and other mineral acids (with 
the exception of the sulphuric acid) are fully confirmed. 
Tartaric, citric and succinic acids, it is true (as was also 
shown in the same work), give out about -Jyth less heat 
than the average of the other acids, but acetic and for¬ 
mic acids fall scarcely A^th below the mean, and oxalic 
acid is always above it. These results, in all their main 
features, are fully corroborated by the experiments re¬ 
corded in this paper, which were performed -with a more 
perfect apparatus and a more exact thermometer than I 
had at my command in my earlier investigations. A 
reference to the same paper will show that while acids, 
differing so widely from one another as oxalic, phos¬ 
phoric, arsenic, nitric, hydrochloric and boracic acids 
scarcely present any sensible difference in the quantities 
of heat which they disengage in combining with the 
bases ; and w r hile of the other acids examined sulphuric 
acid (and probably also sulphurous acid) presents an 
extreme deviation of about -|th above the mean, and the 
tartaric acid group a deviation of about ^th below it, 
the bases, on the contrary (and the subsequent researches 
of Favre and Silbermann have confirmed this result), 
differ altogether in thermal power from one another. 
Thus, equivalents of the oxides of magnesium and of 
silver give out 4-1° and 1-8° of heat respectively in com¬ 
bining with nitric acid, the former oxide having there¬ 
fore 2*3 times the thermal power of the latter. Yet, as 
is well known, both these bases fully saturate the acid, 
and the resulting solutions are even neutral to test- 
paper. For these reasons I have no doubt whatever 
that the first law, as enunciated in 1841, is the expres¬ 
sion of a true physical law*, and that in the combination 
of acids and bases in presence of w*ater the heat dis¬ 
engaged is determined by the base and not by the acid. 
It is true that in this, as in similar physical inquiries, 
experimental results cannot immediately be obtained 
free from complication or disturbing influences. The 
same remark applies to the experimental proof of the 
groat law discovered by Dulong and Petit, wdiich con¬ 
nects the specific heats and atomic weights of the ele- 
