186 Mr. A. B. Northcote on the Function of Salt 



No. III. 



Total number of grains of ammonia absorbed"^ '5654 



by 100 grains of salt J 



Deduct the absorbing power of 1-182 grain of\ .45-19 



sulphate of lime J 



•1135 

 Deduct the absorbing power of 96-702 grains! -lOSO 



of chloride of sodium J 



•0105 



It will be seen that in Nos. I. and III. a slight excess of am- 

 monia remains unaccounted for ; this is partly, of course, due to 

 an unavoidable excess which must in every experiment be added; 

 but I have observed, that throughout the operation, even when the 

 absorption is most active, and even after several hours' contact, 

 there is yet a feeble tinge imparted to the litmus-paper when 

 left in the atmosphere within the bottle for five minutes. This 

 would seem to show, that at all stages of the process there is a 

 certain amount of counteraction going on, and it becomes a great 

 question whether this action — which appears trivial when we deal 

 with a comparatively large amount of ammonia, as in these ex- 

 periments — would not in practice nullify to a great extent, or at 

 least diminish considerably, the absorbent power of this agent, 

 when, spread on the surface of the soil, minute quantities only 

 of ammonia came within the sphere of its action, and the absorp - 

 tion was distributed over a considerable portion of time. 



I believe that this counteraction and liberation of ammonia 

 may be traced to the solubility of the carbonate of lime in the 

 absorbing liquid : upon the adchtion of the first few drops of 

 carbonate of ammonia solution to the solutions of the salts, the 

 small quantity of precipitate which was produced was immedi- 

 ately and perfectly dissolved by agitating the liquid; this was 

 doubtless partly due to the excess of carbonic acid which was 

 evolved from the sesquicarbonate of ammonia, but a considerable 

 portion of the action must be attributed to another cause. It is 

 some time since Professor Connell has shown, that, upon pro- 

 ducing carbonate of lime by the action of carbonate of soda upon 

 chloride of calcium in a medium of distilled water, the carbonate 

 of lime so produced (if produced at all) is held in perfect solu- 

 tion*. I have found the same action to operate to a much larger 

 extent in the case of a saturated solution of chloride of sodium : 

 taking two solutions of chloride of calcium and carbonate of soda, 



* Phil. Mag. S. 3. vol. xxxi. p. 124. 



