1825.] Scientific Notices — Cliemistry. 69 



surfaces of the brick, and in a dry state of the atmosphere, efflo- 

 resces. The action of rain speedily dissolves the efflorescence 

 thus formed, and another portion of salt will be quickly deter- 

 mined to the surface; should this succession of changes continue 

 to go on, the bricks may soon be expected to become porous, 

 and their consequent disintegration must happen in a shoit 

 time. 



If you consider this notice worth inserting in the Atinals of 

 Philosopin/, it may probably be the means of inducing those 

 whom it may more immediately concern, to attend to a circum- 

 stance of which, perhaps, they are not aware. 



I remain, Gentlemen, your very obedient servant, 



M. W. 



2. Solubility of Oxide of Cobalt in Ammonia. — Cobaltic Acid. 



Oxide of cobalt does not appear capable of dissolvino- directly 

 in ammonia, and a combination between the two substances caii 

 take place only under the two following circumstances : — 

 1. Either the oxide of cobalt combines with "an acid, and in this 

 state forms a double salt with the ammonia, which is also com- 

 bined with the same acid ; as, for example, in the carbonate of 

 oxide of cobalt and ammonia, nitrate of oxide of cobalt and 

 anunnnia, &c. 2. Or, when the proportion of acidi:j insufficient 

 to saturate both the oxide of cobalt and the ammonia, as, for 

 example, when a neutral salt of cobalt is treated with an excess 

 of ammonia, there is formed a small quantity of the double salt, 

 and the greater proportion of the oxide precipitates in blue 

 coloured tiocks, which, so long as oxygen gas is excluded, d^ 

 not redissolve. If oxygen gas be admitted, it is rapidly 

 absorbed; the blue flocks at the same time assume a green 

 colour, and gradually disappear, yielding a brown coloured 

 solution. If a salt of cobalt containing an excess of acid be 

 employed, or if there be previously added a sufficient quantity ol" 

 the corresponding ammoniacul salt, the addition of an excess of 

 ammonia occasions no precipitate, and there is obtained a pale 

 red coloured liquid ; in the case of nitrate of cobalt, this liquid 

 undoubtedly contains nitrate of cobalt and ammonia, and de'po- 

 sits red coloured crystals. This solution also is capable of 

 absorbing oxygen gas, and its colour is thereby changed to a 

 brown. Tlie maximuu) amount of absorption is"^ in the propor- 

 tion nearly of one equivalent of oxygen to one equivalent of 

 oxide of cobalt; consequently the cobaltic acid thus formed 

 contains half an equivalent more of oxygen than the hyperoxide 

 of cobalt. 



If the above aminoniacal liquid, previously saturated with 

 oxygen, be conmiitted to a rapid spontaneous evaporation, it 

 yields a compound of ammonia wil/i nitric and cobaltic acids, in 

 brown coloured, apparently four-sided prisms with square 



