•January 28, 1871.] THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
007 
Law 2.—When a neutral is converted into an acid 
salt, by combining with one or more atoms of acid, no 
change of temperature occurs. 
Law 3.—When a neutral is converted into a basic salt, 
by combining with an additional proportion of base, the 
•combination is accompanied with evolution of heat.* * * § * 
Three years later I laid before the Royal Society of 
London the results of an experimental investigation of 
the heat developed when one base is substituted for 
another in chemical compounds. The law deduced from 
this inquiry is implicitly involved in the foregoing, of 
which it may indeed be regarded as a necessary conse¬ 
quence. It was enunciated in the following terms :— 
Law 4.—When one base displaces another from any 
of its neutral combinations, the heat evolved or abstracted 
is always the same, whatever the acid element may be, 
provided the bases are the same.fi 
Finally, the law of metallic substitutions, first an¬ 
nounced in the ‘ Philosophical Magazine ’ for August, 
1844, was thus stated in a paper published in the ‘ Philo¬ 
sophical Transactions’ for 1848. 
Laxo 5 .—When an equivalent of one and the same 
metal replaces another in a solution of any of its salts of 
the same order, the heat developed is always the same; 
•but a change in either of the metals produces a different 
•development of heat. 
In 1845 a paper appeared by Graham on the heat dis¬ 
engaged in combinations, the second part of which refers 
to the heat produced when hydrate of potash is neutra¬ 
lized by different acids. fi The results arrived at by this 
•distinguished chemist exhibit a close agreement with 
those contained in my first communication to the Royal 
Irish Academy. 
The concluding part of the elaborate memoir of MM. 
Tavre and Silbermann on the heat disengaged in chemi- 
•cal actions is chiefly devoted to the same subject. A 
large number of experiments are described, which are 
nearly a repetition of those I had previously published. 
Their results bear a general resemblance to those given 
by myself in 1841, but they widely differ in the details. 
The authors of this able memoir fully recognize the ac- 
•curacy of my fourth law, which asserts the equality of 
thermal effect when one base is substituted for another. 
■“ M. Andrews,” they observe, “ avait en effet etabli que, 
quel que soit l’acide d’un sel, la quantite de chaleur de- 
gagee par la substitution d’une base a une autre pour 
former un nouveau sel est la meme, lorsque l’on con- 
sidere les deux memes bases.” § 
In a preceding paragraph of the same memoir, the 
authors object to what they conceive to be my first law, 
and state that it is not in accordance with the results of 
their investigations. As the question is one of some im¬ 
portance, I may perhaps be permitted to quote the passage 
in the original language. “ Ses conclusions, savoir: que 
la chaleur degagee par I equivalent d’une meme base 
combinee aux divers acides est la meme, ne s’accordent 
pas avec les resultats de nos recherches, et ne nous pa- 
raissent pas pouvoir etre admises.” No doubt, through 
inadvertence, MM. Favre and Silbermann have here 
given an inaccurate statement of my first law. It did 
not declare that precisely the same amount of heat is 
disengaged by all the acids in combining with the same 
base, but that the heat is determined by the base, “ the 
same base producing, when combined with an equivalent 
of different acids, nearly the same quantity of heat.” A 
comparison of the results of MM. Favre and Silbermann 
with those in my original memoir will show that I had 
fully recognized and described the deviations from the 
other acids, exhibited, on the one hand, in excess, by 
* ‘Transactions of the Royal Irish Academy,’ vol. xix. 
j). 228. 
t ‘ Philosophical Transactions ’ for 1844, p. 21. 
X ‘Memoirs of the Chemical Society,’ vol. ii. p. 51. 
§ ‘Annales de Chimie et de Physique,’ 3me scrie. xxxvii. 
p.497 (1853). 
sulphuric acid, and on the other, in deficiency, by tar¬ 
taric, citric and succinic acids. “If we refer,” I re¬ 
marked, in the original memoir of 1841, “to the first, 
second and fourth tables, as being the most extensive, 
from the large number of soluble compounds formed by 
potash, soda and ammonia, it will be observed that sul¬ 
phuric acid developes from 0-8° to nearly 1° more than 
the mean heat given by the other acids ; while tartaric, 
citric and succinic acids fall from 0 - 4° to O’55° short of 
the same. A minute investigation of the influence of 
the disturbing sources of heat will no doubt discover the 
causes of these discrepancies. The high numbers for 
sulphuric acid are probably connected with that acid’s 
well-known property of developing much heat when 
combining with successive atoms of water. All the 
other acids dcvelopo nearly the same amount of heat in 
combining with the same base, the greatest divergences 
from the mean quantity being, in the case of potash, 
+ (P24 0 and — 0T3°; in that of soda, -f- 026° and 
— 0T4°; and in that of ammonia, -fi- 0T7° and — (P05 0 . 
These differences are almost within the limits of the 
errors of experiment.”* 
But although there is a superficial agreement between 
my original results and those of MM. Favre and Silber¬ 
mann, they will be found, when examined closely, to 
differ widely in detail and on points of great importance. 
I had found that oxalic acid disengages almost exactly 
the same amount of heat in combining with the soluble 
bases as hydrochloric, nitric and many other mineral 
acids, and this observation I have always regarded as 
one of the main foimdations of Law 1. MM. Favre and 
Silbermann, on the contrary, have inferred from their 
experiments that “the following organic acids—oxalic, 
formic, valeric and citric—disengage sensibly the same 
quantity of heat, but it is less ( plus faible) than that 
given by the foregoing mineral acids”—among which 
they enumerate the nitric and hydrochloric. According 
to my experiments, no distinction of this kind can be 
admitted between acids derived from the mineral and 
organic kingdom, inasmuch as oxalic acid developes at 
least as much heat in combining with the bases as hy¬ 
drochloric, nitric and several other strong mineral acids. 
The experiments to be described in this paper were 
made some years ago, but their publication has been 
deferred from accidental circumstances. I have, how¬ 
ever, recently repeated a few of the more important 
of them, with a slightly modified form of apparatus. 
The solutions were taken in so dilute a state that the 
heat disengaged never exceeded 3 , 5°C. A standard 
solution of sulphuric acid was prepared and carefully 
analysed, by precipitating a given weight with a soluble 
salt of barium, and weighing the sulphate of barium. 
The strength of the alkaline solutions was adjusted 
with great care by means of this standard acid. The 
same solution of each alkali was employed in all the 
experiments, and the quantity used in each experiment 
was determined by careful weighing. The acid solution 
was of such a strength that, after being mixed with the 
alkali, an excess of two or three per cent, of acid was 
present. The alkaline solution was contained in a light 
glass vessel, in which a large platinum crucible holding 
the acid was carefully floated. By giving a rapid rota¬ 
tion, by means of a light stirrer, to the acid solution in 
the platinum crucible, a perfect equilibrium of tempera¬ 
ture was soon established between the two liquids. The 
initial temperature of the solutions was usually about 
1 -5° below that of the air, and the final temperature of 
the mixture about 1*5° above it. The corrections for the 
heating and cooling action of the surrounding medium 
were determined with great care. The mechanical process 
of adding the acid to the alkaline solution produced no 
change of temperature, and as the heat disengaged in 
the combination raised the liquid almost instantly to the 
* ‘ Transactions of the Royal Irish Academy,’ vol. xix. 
p. 249. 
