326 SALT, NITRATE OF SODA, SALTS OF AMMONIA, ETC. 



sionally also of potash, but mostly in inappreciable 

 quantities. The alkalies, as well as the lime and the 

 magnesia, seem to be dissolved by the agency of or- 

 ganic matters, as the dried residues blackened upon 

 heating, and effervesced with acids after ignition. 



Quantities of magnesia dissolved severally out of 300 grammes 

 of earth by one litre of 



Distilled water. Gypsum water. 



Milligr. of magnesia. Milligr. of magnesia. 



Bogenhausen earth 3O2 70'6 



Schleissheim " 31'6 878 



Bogenhausen subsoil 12*2 84'2 



Earth from Botanic Gardens 45-4 168-6 



" Bogenhausen, No. L* 26'6 101 '6 



" " No. II. 38-2 98-0 



Schornhof 8'6 634 



a cotton field, Alabama 1-9 3 '8 



These figures show that dressing a field with sul- 

 phate of lime makes the magnesia in the soil soluble 

 and distributable. If the action which gypsum exer- 

 cises upon the growth of clover depends really upon 

 an increased supply of magnesia, this must surely be 

 looked upon as one of the most curious facts known, 

 since the increased supply is effected here by the aid 

 of a lime salt. An experiment, made specially for the 

 purpose, showed that the contact of arable earth with 

 the solution of sulphate of lime is attended by an actual 

 substitution of magnesia for lime ; that is to say, a cer- 

 tain quality of lime is withdrawn from the solution and 

 combines with the earth, whilst the liberated sulphuric 

 acid, which was united to the lime, withdraws from the 

 earth an equivalent quantity of magnesia. In a litre 

 of gypsum water which had been in contact with 300 

 grammes of earth from a wheat-field, there were found 

 the following quantities of sulphuric acid, magnesia, and 

 lime : 



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

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

 Avith gypsum, No. II. had. 



