of Edinburgh, Session 1869-70. 
79 
genised : — Twenty grammes of cane sugar were dissolved in 150 
grms. of water, and inverted through the action of 2 grms. of 
sulphuric acid, keeping the solution at the temperature of 70° C., 
afterwards adding pure carbonate of barium, filtering, and then 
adding one gramme of sodium in the form of a weak amalgam. 
The action took place without any evolution of hydrogen. If 
the amalgam was impure, from the presence of other metals, it 
evolved hydrogen at once, and the solution became brown ; other- 
wise it remained perfectly clear. After one month the solution 
gave no trace of sugar with the alkaline copper solution. It was 
then carefully neutralised with dilute sulphuric acid, evaporated 
on the water bath, the greater part of the sulphate of sodium 
separated by crystallisation, and the residue treated with boiling 
70 per cent, alcohol, the solution filtered, and allowed to crys- 
tallise. Sometimes the mannite did not crystallise until all the 
alcohol had evaporated, leaving a syrup that slowly assumed the 
crystalline form. The product had no rotatory power. In no 
case was the sugar entirely changed into mannite — a gummy sub- 
stance was invariably left, that would not crystallise after expo- 
sure to the air for months. Mannitan, or some similar body, 
may be one of the products. 
Dextro-glucose made from honey gave mannite when treated 
in the same way, having exactly the same melting point as ordi- 
nary mannite. In treating milk sugar with dilute sulphuric acid, 
changing into gallactose and hydrogen ising, dulcite was not iso- 
lated ; but I have not specially studied the reaction. 
3. On the Flow of Electricity in Conducting Surfaces. By 
W. R. Smith, M.A., Assistant to the Professor of Natural 
Philosophy in the University of Edinburgh. Communi- 
cated by Professor Tait. (With a Plate.) 
The conditions of a steady flow of electricity in a conducting sur- 
face are completely determined, if we know either the nature of 
the electrical distribution throughout the surface, or the direction 
and intensity of the flow at every point. On the first of these ways 
of considering the question, the problem is solved if we can express 
the potential v at any point as a function of the co-ordinates, and 
