ELECTROLYSIS OF SECONDARY COMPOUNDS. 
13 
was subjected to exactly the same treatment as the preceding- double salt, and 
the results were precisely similar. 48 cubic inches of hydrogen were collected from 
the platinode. When ammonia was added in excess to the solution in the platinode 
cell no precipitate was produced, which proved the absence of alumina. Evaporated 
to dryness, the saline residue was ignited, and weighed 21 grains. It was sulphate 
of potassa, and the amount, as before, was within one grain of the quarter of an equi- 
valent. 
(u.) Some of the double sulphate of magnesia and potassa (MgO, S0 3 , -|- KO, S0 3 ) 
was carefully prepared, and submitted in solution to the same treatment. After 
48 cubic inches of hydrogen had been collected the platinode solution was evapo- 
rated to dryness, and left a saline residue of 36'6 grains. This was redissolved 
and treated with carbonate of potassa. A precipitate of carbonate of magnesia was 
thus obtained, which was reconverted into sulphate, and weighed 3‘8 grains ; this 
was equivalent to 0'76 grain of magnesium, to which must be added 0*24 grain re- 
covered from the wash water by means of phosphate of ammonia, making the total 
quantity of magnesium which had passed over to the platinode TO, or about ^th of 
an equivalent. Deducting the total amount of sulphate of magnesia, 4’98 grains, from 
the mixed sulphates, 36'6 grains, we have 3T62 as the amount of the sulphate of 
potassa. 
Thus it appeared that the three bases, alumina, magnesia, and oxide of copper, or 
their metals, when in combination with sulphuric acid and potassa, refused to travel 
from the zincode to the platinode under the influence of the voltaic current into an 
acid with which they were capable of forming an immediate and soluble combina- 
tion. Could it be that the same results might follow from the electrolysis of the 
single salts of the same acid ? 
(w.) Some pure sesquisulphate of alumina (Al 2 0 3 , 3S0 3 ) was prepared by preci- 
pitating alum with excess of ammonia, thoroughly washing the precipitate and redis- 
solving it in sulphuric acid, with the aid of heat. An excess of alumina was left, from 
which the liquid was separated by filtration. It was then evaporated till it solidified 
upon cooling. The mass was subjected to pressure in calico, and the dry salt dis- 
solved in water. 
The zincode and connecting cells of the diaphragm apparatus were then charged 
with the solution, and the platinode cell with dilute sulphuric acid. The arrange- 
ment conducted well, and in half an hour 13 cubic inches of oxygen were collected 
from the zincode. The process was then stopped, and on supersaturating the liquid 
at the platinode with ammonia, the slightest possible trace of alumina was precipi- 
tated. 
Thus it again appeared that the electrolysis was carried on without the transfer of 
the base or its metal to the platinode. 
Was the peculiar constitution of this salt as a sesqui compound concerned in any 
way in this result ? 
