’ TRANSACTIONS OF THE SECTIONS. 33 
by the fact which has been before established by the author, that the hydrate of lime 
when combining with the acids developes more heat than the hydrate of potash. But, 
_ in accordance with the principle before stated, the diminution of temperature is the 
_ same with equivalents of all the salts of lime. In an inquiry of this kind many pre- 
cautions are requisite, in order to obtain accurate results. Among the most important 
may be mentioned, the exact neutrality of the salt to be decomposed, a perfect equa- 
lity of temperature in the solutions before mixture, and the precipitation of the oxide 
in the state ofa pure hydrate, and not of a subsalt. 

‘ 
if 
x 
On the Calorific Effects of Magneto-Electricity, and the Mechanical Value 
} of Heat. By J. P. Jourz. 
_ Although it had been long known that fine platinum wire can be ignited by mag- 
_ neto-electricity, it still remained a matter of doubt whether heat was evolved by the 
: coils in which the magneto-electricity was generated: and it seemed indeed not un- 
reasonable to suppose that co/d was produced there, in order to make up for the heat 
_ evolved by the other parts of the circuit. The author had endeavoured therefore to 
_ clear up this uncertainty by experiment. His apparatus consisted of a small com- 
pound electro-magnet, immersed in water, revolving between the poles of a powerful 
Stationary magnet. The magneto-electricity developed in the coils of the revolving 
electro-magnet was measured by an accurate galvanometer; and the temperature of 
the water was taken before and after each experiment by a very delicate thermo- 
meter. The influence of the temperature of the surrounding atmospheric air was 
guarded against by covering the revolving tube with flannel, &c., and by the adoption 
of a system of interpolation. By an extensive series of experiments with the above 
apparatus the author succeeded in proving that heat is evolved by the coils of the 
_ Mmagneto-electrical machine, as well as by any other part of the circuit, in proportion 
_ to the resistance to conduction of the wire and the square of the current ; the mag- 
_ neto-, having, under comparable circumstances, the same calorific power as the voltaic 
electricity. Prof. Jacobi, of St. Petersburgh, had shown that the motion of an elec- 
_ tro-magnetic engine generates magneto-electricity in opposition to the voltaic current 
of the battery. The author had observed the same phenomenon on arranging his 
_ apparatus as an electro-magnetic engine; but had found that no additional heat was 
_ evolved on account of the conflict of forces in the coil of the revolving electro-mag- 
_ net, and that the heat evolved by the coil remained, as before, proportional to the 
_ square of the current. Again, by turning the machine contrary to the direction of 
_ the attractive forces, so as to increase the intensity of the voltaic current by the as- 
sistance of the magneto-electricity, he found that the evolution of heat was still pro- 
portional to the square of the current. The author discovered, therefore, that the 
__ heat evolved by the veltaic current is invariably proportional to the square of the 
_ current, however the intensity of the current may be varied by magnetic induction. 
_ But Dr. Faraday had shown that the chemical effects of the current are simply as its 
_ quantity. Therefore he concluded that in the electro-magnetic engine, a part of the 
_ heat due to the chemical actions of the battery is lost by the circuit, and converted 
~ into mechanical power ; and that when the electro-magnetic engine is turned contrary 
_ to the direction of the attractive forces, a greater quantity of heat is evolved by the 
_ cireuit than is due to the chemical reactions of the battery, the overplus quantity 
__ being produced by the conversion of the mechanical force exerted in turning the ma- 

























chine. By a dynamometrical apparatus attached to his machine, the author has ascer- 
tained that, in all the above cases, a quantity of heat, capable of increasing the tem- 
_ perature of a pound of water by one degree of Fahrenheit’s scale, is equal to a me- 
hanical force capable of raising a weight of about 838 pounds to the height of one 
Oot. 
a ie 
é ‘On the Decomposition of Carbonic Acid Gas, and the Alkaline Carbonates, 
by the light of the Sun. By Prof. Draper, New York. 
_ The decomposition of carbonic acid gas by the leaves of plants under the influence 
of the light of the sun, is one of the most remarkable facts in chemistry. Dr. Dau- 
3 in a very able paper in the Transactions of the Royal Society for 1836, came 
43. D 





