MAXIMUM SPECIFIC ELECTRICAL CONDUCTIVITY IN CHEMISTRY. 127 
If the quantities of free iodine and hydrogen sulphide be kept small, the direction 
of the whole reaction appears to depend mainly, if not solely, on whether the solution 
of hydriodie acid be premaximal or ultramaximal, and the velocity of the reaction in 
either direction depends on the value for y=K,x,.—K. It is only from premaximal 
solutions of hydrogen iodide that the last traces of free iodine disappear altogether. 
Beuwaviour or Nitric Actp. 
Nitric acid and highly concentrated aqueous solutions of nitric acid undergo partial 
decomposition when exposed to light. The concentration of nitric acid corresponding 
to maximum conductivity lies between 28°5 and 29 per cent. HNO,. At lower con- 
centrations nitric acid is quite stable under the influence of light. 
Peroxide of nitrogen and water are products of this photochemical decomposition. 
As this decomposition progresses there must be in such concentrated solutions a rise in 
conductivity, consequent upon the dilution of the acid. 
In order to throw light on this behaviour of nitric acid, a number of solutions were 
prepared having known concentrations higher and lower than the maximum. Pure 
nitric oxide gas was passed into these solutions. With the solutions having concentra- 
tions higher than nitric acid of maximum conductivity colours were obtained passing 
from yellow-brown in the more concentrated solutions through green in less concentrated 
solutions, to pure blue in solutions only slightly more concentrated than the maximum 
acid. None of the solutions weaker than the maximum acid had any oxidising action 
on the nitric oxide, and they therefore remained perfectly colourless. Thus in nitric 
acid of 36 per cent. the blue colour was readily obtained, whereas an acid of 28 
per cent. HNO, remained quite colourless. Decomposition of nitric acid in pre- 
maximal solutions could only imply a lowering in specific conductivity. They are not 
decomposed either by light or by nitric oxide. 
Tue Action oF SuueHuRIC AcID ON CANE-SUGAR. 
According to its concentration sulphuric acid may be used either to hydrolyse or to 
dehydrate cane-sugar. 
If to excess of concentrated sulphuric acid containing 84 per cent. H,SO, a little 
| of a concentrated solution of cane-sugar be added, charring sets in rapidly and is soon 
complete. On progressive dilution from this point onwards the time taken to char the 
sugar increases. When the acid has been diluted to about 30 per cent. H,SO,, it may 
be left for many days along with dissolved cane-sugar at the ordinary temperature, and 
the solution may even be boiled for several minutes without the slightest indication 
of charring. 
Finally, in solutions of more dilute sulphuric acid, the chief reaction is of an 
