390 



THE SOUTHERN PLANTER. 



pounds containing, in addition to silica, 

 more than one other substance, by the 

 name of simple silicates. These com- 

 pounds are characterized by a great ten- 

 dency of uniting together amongst them- 

 selves, and forming a new class of saline 

 compounds — that of the double silicates. 

 Thus silicate of alumina and silicate of 

 lime frequently are found in nature united 

 together to form one substance — a double 

 silicate ; other double silicates are the 

 compounds of silicate of soda and lime, 

 or silicate of potash and alumina, &c. 

 Several of the double silicates, containing, 

 in addition to silicate of alumina, other 

 bases, have lately been artificially pre- 

 pared by Professor Way, who is of opin- 

 ion that the absorption of ammonia by the 

 soil from the atmosphere is dependent on 

 the formation of a double silicate of alum- 

 ina and ammonia, a compound which is 

 always produced when any of the other 

 double silicates, consisting of silicate of 

 alumina and another base, is brought in 

 contact with the carbonate of ammonia 

 contained in the atmosphere. According 

 to Professor Way, the compounds of sili- 

 cate of alumina with soda, lime, mag- 

 nesia, or potash, not only have the power 

 to fix the ammonia in solution, but also 

 the gaseous carbonate of ammonia of 

 the atmosphere. The examination of 

 several of these double silicates has 

 brought to light some important facts. 

 Thus it has been shown that the double 

 silicate of alumina and soda, when digest- 

 ed with a solution of a lime salt, gives 

 rise to a new compound, a double silicate, 

 containing lime instead of soda. In this 

 new compound, the lime in its turn may 

 be replaced by magnesia, and this base 

 again by potash. The double silicate 

 of alumina and potash is finally deprived 

 of its potash by ammonia, which entering 



into combination with the remaining sili- 

 cate of alumina, thus gives rise to the 

 formation of the double silicate of alumi- 

 na and ammonia. It will be observed 

 that there is a regular order of decom- 

 position between the silicates of each 

 base, and the ordinary salts of other base,s; 

 and it is especially important to remem- 

 ber, that ammonia displaces all other 

 bases from their union with silicate of 

 alumina. Thus a salt of ammonia not 

 only decomposes the double silicate of 

 alumina and potash, giving rise to the 



double silicate of alumina and ammonia, 

 but whenever a salt of ammonia in solu- 

 tion, and also the carbonate of ammonia 

 in the atmosphere, comes in contact with 

 the soil containing any one of the other 

 double silicates, ammonia is invariably ab- 

 sorbed, and the other base in combina- 

 tion with silicate of alumina is sepa- 

 rated. An especially careful provision 

 thus manifests itself, in the solicitude of 

 the soil to prevent the loss of the most 

 valuable fertilizing constituent of ma- 

 nures ; and it is interesting to observe, 

 that the power of soils to retain fertilizing 

 constituents, in so far as this is depen- 

 dent on the presence of double silicates, 

 is proportional to the relative importance 

 of the different fertilizing constituents. 

 Ammonia, as far as we know, is the most 

 valuable of all manuring substances ; 

 potash follows next in importance ; and 

 lime, which occurs in nature far more 

 abundantly than either ammonia or pot- 

 ash, is justly regarded as being of less 

 consequence ; whilst soda appears to be 

 still less important in relation to the dif- 

 ferent vegetable processes, than either 

 ammonia, potash, lime, or magnesia. 



Now, it is exceedingly interesting to ob- 

 serve the order in which these different 

 bases replace each other in the double 

 silicates. This order has been deter- 

 mined by Professor Way, as follows : — 



Soda, Lime, Magnesia, Potash, Ammonia, 



that is to say, in the double silicate of 

 alumina and soda, the soda may be re- 

 placed by lime, magnesia, potash, or am- 

 monia, which is simply effected by bring- 

 ing the soda double silicate in intimate 

 contact with any soluble salt of the bases 

 named. The lime double silicate, again, 

 is decomposed by the bases which follow 

 it in the list, but not - by soda, which pre- 

 cedes it, and we thus find that potash is 

 only turned out from its silicate by ammo- 

 nia, whilst of itself it is capable of dis- 

 placing the less valuabe bases, soda, lime, 

 and magnesia. In other words, for the pre- 

 servation of ammonia four compounds are 

 made answerable, for that of potash only 

 three, and for soda, the least valuable, ap- 

 parently no provision is taken by the soil 

 to prevent its free escape with the water 

 draining through the soil. There are 

 several points which have to be attended 

 to in forming correct views on the nature 



