144 Notes and Queries. [No. 7, new series, 



and the atom of base will hold this atom of acid with very con- 

 siderable force, in fact nothing short of a stronger chemical affinity 

 or a high degree of temperature, can separate this atom of acid 

 from the atom of base, the case however is very different should 

 the salt carbonate of lime combine with a second atom of carbo- 

 nic acid, so as to become a bi-carbonate of lime, since instead of 

 holding the second atom of carbonic acid with a degree of force 

 equal to that with which the first atom is held, the force is so 

 feeble, that it is liable to be overcome by the slightest change of 

 circumstances, mere evaporation of the watery particles of the 

 fluid in which the bi-carbonate may be is sufficient to cause the 

 separation of the second atom of carbonic acid, and consequently 

 to determine the deposition of the carbonate. The solvent for the 

 carbonate being the second atom of carbonic acid, and as soon as 

 this is evolved there is nothing to prevent the carbonate from re- 

 turning to its insoluble state and it does so accordingly. In the 

 instance of the substance sent to me for examination, the deposi- 

 tion has been effected by the attraction of a solid causing the 

 liberation of carbonic acid gas. The action, however, in this par- 

 ticular case, does not stop here, — the deposit is continually washed 

 by water containing soluble silicic acid and soluble silicates, these 

 are continually causing a further elimination of carbonic acid ; 

 silicates of alkalies and alkaline earths being formed, while the 

 carbonic acid set free either escapes into the atmosphere, or as the 

 case may be seizes any portions of free alkali at hand. It is a 

 familiar fact that when water is artificially impregnated by carbo- 

 nic acid mere exposure with diminished pressure, allows of the 

 escape of this gas, the escape is more rapid, if the water be pour- 

 ed or allowed to flow, while in contact with the atmosphere and 

 relieved from abnormal pressure. Still more rapid is the effect, 

 if water whether naturally or artificially impregnated with carbo- 

 nic acid be boiled, and in this last case, if the alkaline earths or 

 iron be in the soluble form as bi-carbonates, they are (during the 

 ebulition) precipitated in the form of carbonates to the bottom of 

 flask or other vessel in which the carbonated water was held. 

 Finally if either naturally or artificially the water is kept under 

 pressure, and the source of the carbonic acid is continually pre - 



