34 Proceedings of Royal Society of Edinburgh. [sess. 
At a temperature of 18° C. the concentrations of aqueous 
solutions of these acids, which correspond to their respective 
maximum conductivities as determined by Kohlrausch, are - 
Hydrochloric Acid, . . 18*3 per cent. 
Nitric „ ... 29*7 „ 
Sulphuric „ ... 30‘4 „ 
The following reactions have been investigated : — 
The de-liydration by hydrochloric acid of hydrated cobaltous 
chloride. — The deep blue colour of anhydrous cobaltous chloride is 
immediately produced on adding a few drops of the pink solution 
of the hydrated salt to an excess of hydrochloric acid solution of 
28 per cent. HC1 and upwards. With acid of 24 per cent, the 
blue coloration is still distinct. With acid of 22 per cent, it is 
very slight. With acids below 18 per cent, it is imperceptible. 
The de-hydration of sugar by sulphuric acid. — If a small 
quantity of cane-sugar syrup be mixed with solutions of sulphuric 
acid of 36 per cent. H 2 S0 4 and upwards, and if the mixture be 
raised momentarily to the boiling point, proper precaution being 
taken to avoid local over-heating, a deep brown coloration is 
rapidly produced. Solutions of 30 per cent. H 2 S0 4 and lower, 
treated in the same manner, either remain colourless, or only 
slowly acquire a faint yellow tinge. 
Reduction of chromic anhydride by hydrocJiloric acid. — Concen- 
trated solutions of this acid rapidly reduce chromic anhydride at 
ordinary temperature, the orange red colour of chromic anhydride 
giving place to the pure green colour of solutions characteristic of 
chromic chloride within a few hours. As the dilution of the acid 
is increased towards maximum conductivity, the velocity of this 
reaction diminishes. In one experiment with 24 per cent, acid, 
the reduction was complete in about 100 hours; while in another 
experiment with 18 per cent, acid, which was begun on July 22, 
1897, the reduction is still incomplete, in spite of the fact that the 
test-tube was only loosely closed by an ordinary cork, the lower 
end of which has been bleached by the escaping chlorine gas. 
Oxidation of hydrogen iodide by sulphuric acid. — On adding 
about 2 centigrams of potassium iodide in dilute solution to 38 
cubic cms. of sulphuric acid of 45 per cent, and upwards, the liber- 
ation of iodine at ordinary temperature became perceptible within 
