On the Electrolysis of Secondary Compounds. 349 



instance a solution of bicarbonate of magnesia is formed, and 

 an insoluble carbonate containing a smaller proportion of car- 

 bonic acid; and in the other, that the same insoluble subcar- 

 bonate is produced, but without the solution of bicarbonate, 

 the proportion of carbonic acid required for this being ex- 

 pelled in the form of gas. The results of the trials I have 

 made have not confirmed either of these conclusions. It has 

 appeared to me to dissolve both in hot and in cold water, 

 without undergoing any decomposition. I have not been able 

 to obtain an insoluble subcarbonate of magnesia by acting on 

 the prismatic salt by cold water, or carbonic acid gas from it 

 by boiling water, for instance, boiling it in distilled water in a 

 retort connected with a mercurial pneumatic apparatus. It 

 is true, that when this carbonate is thrown into hot water, 

 there is a disengagement of air, but the air is common air me- 

 chanically entangled, not carbonic acid gas which had been 

 chemically combined. 



Both the hot solution and the cold, on evaporation, yielded 

 the prismatic compound. 1000 grains of water at the tempera- 

 ture of 60 appear capable of holding in solution about four 

 grains; thus 326'6 grains of the solution of carbonate, after the 

 excess of carbonic acid gas had been expelled by the air-pump, 

 afforded on spontaneous evaporation 1*5 grain of crystalline 

 salt. 



Whether this slight degree of solubility can be useful, con- 

 sidering the qualities of the compound as a medicine, or 

 whether the crystalline spicular prismatic form which it as- 

 sumes on separation of the excess of carbonic acid by which 

 the carbonate was brought into solution can be injurious to 

 the coats of the stomach, as a mechanical irritant, it is far 

 from easy to determine; the probability is, reasoning analo- 

 gically, that neither the one nor the other circumstance, me- 

 dicinally considered, is of much consequence. 



Fort Pitt, Chatham, Oct. 1, 1840. 



LII. An Abstract of Professor Daniell's Papers on the Electro- 

 lysis of Secondary Compounds, in the Philosophical Trans- 

 actions for 1839 and 184-0. 



IT has been long known that when a saline solution is sub- 

 jected to the action of a galvanic current, both the water 

 and the salt that it contains are resolved into their constitu- 

 ents; oxygen and the acid being evolved at the zincode, whilst 

 hydrogen and the base appear at the platinode. The primary 

 object of these researches was the determination of the re- 

 lative proportions of these decompositions, and their relation 



