Chemistry and Physics. 4038 
Boussingault’s recent observations on the amount of carbonic 
acid decomposed by a given area of green leaf seem to me to 
afford interesting data for a new deter iMbnaion of the efficiency of 
sunlight. By experiments made between the months of January 
and October under the most favorable circumstances in atmo- 
spheres rich in CO2, one square ae ae of leaf was ey! ha 
a id in one hour, as a mean, 5°28 cub. centims. of CO®, 
in darkness to evolve. during the same period of time 0°33 bah 
centim . of CO?, In other words, one ie er metre of Ee 
The Giihaitity of avery e acid decomposed does not represent 
the whole work of sunlight for the time, as water is simultane- 
laborious researches on vegetable physiology, says, “Si l’on envi- 
Sage la vie végétale dans son ensemble, on est convaincu que la 
feuille est la premiére 6tape des glucoses que plus ou moins m odi- 
8, on trouve répartis dans les diverses parties de l’organisme ; 
que e’est la feuille qui les élabore aux Sat de Pacide carbonique 
et de Peau.”"—dnn. de Chemie, tom. xiii, p 415. e funda- 
Mental chemical reaction taking place in the leaf may therefore 
be represented as follows 
Be UU. Be) ee ED ee OO 
(2 age FO mee" te OF 
tape sugar. : 
absorption of a large amount of energy ; : if we enue 
i i ‘0 Ay “HE, 
which can he shown to be very little, the calculated result is made 
& Maxim whereas the gongeneapian of (2) pte attended with 
an evolution of heat, diminishes considerably the amount of 
Power required, Happily Preakicod's he determination of the 
thermal value of grape-sugar leaves no doubt as to the true equiv- 
alent of work done in its formation. Taking the following 
* The rate at which the leaf functions is dependent on the luminous intensity. 
The relative amounts, apenas of carbonic acid decomposed through the action 
of the different colored rays are proportional to their luminous power; and the 
curve of mange cigeed is found to follow the curve of Fraunhofer. This proves that 
the sie ings we form of equal luminous impressions is in reality due to equal 
a, ; ; 
\ 
into two postions ° 
identical thermal effects by absorption. This does not prove = each ray has the 
total energy, but only that in all probability those at equal distances 
enter nda of te mea ve-length in ‘dis ndrinall ‘ght-epectrure of the nuh 
