248 Prof. Daniell and Dr. Miller on the 



ness, 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 equivalent. 



{ic.) Some of the double sul-phatc of magnesia and potassa 

 (MgO, SO3, +KO, SO3) was carefully prepared, and sub- 

 mitted in solution to the same treatment. After 48 cubic inches 

 of hydrogen had been collected the platinode solution was 

 evaporated 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 recovered from the wash water by means 

 of phosphate of ammonia, making the total quantity of magne- 

 sium which had passed over to the platinode TO, or about y'^gth 

 of an equivalent. Deducting the total amount of sulphate of 

 magnesia, 4*98 grains, from the mixed sulphates, 36*6 grains, 

 we have 31*62 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 cur- 

 rent into an acid with which they were capable of forming an 

 immediate and soluble combination. Could it be that the 

 same results might follow from the electrolysis of the single 

 salts of the same acid ? 



(to.) Some pure sesqiiisulphate of alumi7ia (Alg O3, 3SO3) 

 was prepared by precipitating alum with excess of ammonia, 

 thoroughly washing the precipitate and redissolving it in sul- 

 phuric 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 dissolved in 

 water. 



The zincode and connecting cells of the diaphragm appa- 

 ratus were then charged with the solution, and the platinode 

 cell with dilute sulphuric acid. The arrangement conducted 

 well, and in half an hour 13 cubic inches of oxygen were col- 

 lected 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 precipitated. 



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 scsqui com- 

 pound concerned in any way in this result ? 



[x.) A salt of the same order, viz. the sesquisulphate of iron 



