246 The Power of Soils to 



We have mentioned the influence of mere mechanical 

 conditions in modifying, or even for the time setting aside, 

 the ordinary laws of chemical action ; as we quoted, as an 

 illustration, the action of sulphate of ammonia on chalk. 

 Another and a very curious example of the same sort of 

 effect is shown in the mutual action of common salt and 

 chalk. It is a well-known fact that a solution of common 

 salt has no chemical action on chalk ; indeed, when solu- 

 tions of muriate of lime and carbonate of soda are mixed 

 together, the salts are both decomposed, a mixture of com- 

 mon salt and chalk is the result, and, however long these two 

 substances are left together, no further change takes place. 

 If, however, a quantity of sand is added, and the mixture 

 exposed to the air, but protected from the rain, it will be 

 found in a short time that the two substances react on each 

 other, and give rise to the reproduction of those very sub- 

 stances, by the mutual action of which they have themselves 

 been formed. A dry mixture of salt and chalk remains 

 wholly unchanged, and so also does one which is thoroughly 

 wetted ; but if it is divided by the addition of soil or sand, 

 and kept moist, both substances are partially decomposed, 

 and the decomposition which then takes place is directly 

 opposed to the ordinary known laws of chemical combina- 

 tion. It is plain, then, that the action of salt on any soil 

 must, in great part, depend upon the mechanical condition of 

 the latter ; and whether the circumstances are such as to 

 favor the decomposition of the salt, and the consequent 

 formation of carbonate of soda, A little more or less rain 

 may make all the difference, by preventing or assisting in the 

 decomposition of the salt. This fact, which has been known 

 some time, derives additional weight from Mr. Way's experi- 

 ments. 



Our soil being mostly a retentive clay we have been ena- 

 bled to perceive perhaps more readily, the effects of repeated 

 applications of guano ; for we have found a vast difference in 

 favor of this manure over stable dung, costing twice the 

 amount of the guano. 



