346 SALT, XITEATE OF SODA, SALTS OF iOIMONIA, ETC. 



magnesia and potash taking its place, quite contrary to the 

 ordinary affinities. 



The experiments were made as follows: — 300 grammes 

 of each earth were mixed with a htre of pm-e water, and 

 300 other grammes of the same earth with a htre of a 

 saturated solution of gypsum. After twenty-four hours 

 the fluid was filtered, and the filtrate tested for magnesia. 

 Pure distilled water took up from all the experimental 

 earths, sulphuric acid and chlorine, besides traces of hme, 

 magnesia, and soda, and occasionaUy also of potash, but 

 mostly in inappreciable quantities. The alkahes, as well 

 as the hme and the magnesia, seem to be dissolved by the 

 agency of organic matters, as the dried residues blackened 

 upon heating, and effervesced with acids after igTiition. 



Quantities of magnesia dissolved severally out of 300 grammes of earth 

 by one litre of 



These figures show that dressing a field with sulphate 

 of hme makes the magnesia in the soil soluble and dis- 

 tributable. If the action which gypsum exercises upon 

 the growth of clover depends reaUy upon an increased 

 supply of magnesia, this must surely be looked upon as 

 one of the most curious facts known, since the increased 



* On this field it had been experimentally proved that dressing with 

 gypsum would give a larger clover crop. No. I. had not yet been 

 manured with gypsum, No. II. had. 



