834 Proceedings of the Poyal Society 
in the chlorine cell, is 1578 heat units. The number given by Nau- 
mann is 1736 heat units. Naumann’s value, with a correction 
which has not been made for the heat of solution of chlorine, is 
about 1660 heat units. The heat of formation of Cu 2 Cl 2 from the 
E.M.F. of copper in the chlorine cell is 493 heat units. The number 
given by Naumann is 517 heat units. 
We have made a few experiments with a bromine cell, but as we 
have not made any with a copper bromide cell, it is unnecessary 
to give them at present. 
One experiment is mentioned in this paper, testing the influence 
of temperature on the E.M.F. of the iodine cell. This has become a 
matter of some importance. In a paper by Helmholtz, to which we 
referred in our last communication, it is shown that the difference 
of E.M.F. at different temperatures is possibly the measure of the 
work done in the cell which does not appear in the electric current. 
In conclusion, the results derived from the iodine and cuprous 
iodide cell seem fairly satisfactory. 
Probably the best way to test the accuracy of the method would 
be to run down an iodine cell in a calorimeter, and compare the 
heat evolved by the solution of a given weight of zinc with the 
value calculated from the electromotive force of the cell. We pro- 
pose to make some experiments in this direction. 
6. On the Nature of Solution. By Mr. W. L. Goodwin. 
Communicated by Professor Crum Brown. 
7. Diagnoses plantarum novarum et imperfecte descriptarum 
Phanerogamarum Socotrensium, quas elaboravit Bayley 
Balfour, Scientiae Doctor et in Universitate Glascuensi 
rerum botanicarum regius professor. Pars Altera. 
RUBIACEiE. 
58. Dirichletia venulosa, Balf. fit . : frutex 10-pedalis ; foliis 
oblongis v. oblongo-lanceolatis basi angustatis vix petiolatis acutis v. 
obtusis coriaceis margine revolutis, subtus venulis nigris perspicuis 
