190 PHOSPHATES OF PC TASH, AND CHLORIDE OF SODIUM. 



cept in the living plant, and as they are too expensive to be ever em- 

 ployed as manures, it is the less Jo be regretted that few experiments 

 have yet been tried with the view of ascertaining their effect upon vege- 

 tation. 



9°. Phospf^tes of Potash. — If to a known weight of phosphoric acid 

 (p. 186) pearl-ash (carbonate .of potash) be added as long as any effer- 

 vescence appears, and the solution be then evaporated, phosphate of 

 pot^h is obtained. If to the solution before evaporation a second por- 

 tion of phosphoric acid be added, equal to the first, and the water be 

 then expelled by heal, B\-phosphate of potash will remain, [so called 

 from his^ twice, because it contains ticice as much acid as the former, or 

 neutral phosphate.] 



One or other of ihese two salts is found in the ash of nearly all plants. 

 Whether or not the elements of which they consist exist in this state of 

 combination in the living plant will be considered hereafter, in the mean 

 time it may be stated as certain that they are of the most vital impor- 

 tance not only in reference to the growth of plants themselves, but also 

 to their nutritive qualities when eaien by animals for food. 



These phosphates are occasionally, perhaps very generally, present 

 in the soil in minute quantities, and there is every reason to believe 

 that could they be applied to the land in a sufficiently economical form, 

 they would in many cases act in a most favourable manner upon vege- 

 tation. They are contained in urine and other animal manures, and to 

 their presence a portion of the efficacy of these manures is to be ascribed. 



VI. SODIUM, SODA, CARBONATE OF SODA, SULPHATE OF SODA, SULPHU- 



RET OF SODIUM, CHLORIDE OF SODIUM. 



1°. Chloride of Sodium, common or sea salt, exists abundantly in sea 

 water, and is found in many parts of the earth in the form either of in- 

 crustations on the surface or of solid beds or masses at considerable depths. 

 The rock salt of Cheshire is a well known example of this latter mode 

 of occurrence. 



Common salt may also be detected in nearly all soils, it is found in 

 the ashes of all plants, but especially and in large quantity in the ashes of 

 marine plants (kelp), and is sometimes borne with the spray of the sea to 

 great distances inland, when the winds blow strong, and the waves are 

 high and broken. 



On some rocky shores, as on that between Berwick and Dunbar, the 

 spray may be seen occasionally moving up the little coves and inlets in 

 the form of a distinct mist driving before the wind, and the saline matter 

 has been known to traverse nearly half the breadth of the island before 

 it was entirely deposited from the air. 



It is impossible to calculate how much of the saline matter of sea water 

 may in this way be spread over the surface of a sea-girt land like ours ; 

 but two things are certain — that those places which are nearer the sea 

 will receive a greater, and those more inland a lesser, portion ; and that 

 those coasts on which sea winds prevail will be more largely and more 

 frequently visited than those on which land winds are more' commonly 

 experienced. 



It is well known that common salt has been employed in all ages and 

 in all countries for the purpose of promoting veg3tation, and in no coun- 



