ADVERTISEMENT 

 TO THE FOURTH EDITION. 



The present edition is enriched with a large number of recent 

 analyses of manures ; and especially of the ashes of plants, 

 which will be found in the Appendix to Part I. The greater 

 number of these analyses have been made under the eye of the 

 Author in the Laboratory at Giessen, and with the aid of the 

 most improved methods. 



At the request of Professor Liebig I assisted in the preparation 

 of the last edition of this Work, the various engagements of Dr. 

 Playfair having so fully occupied his time as to preclude him 

 from giving the requisite attention to it. The same causes have 

 led to my undertaking the entire revision of the present edition. 



WILLIAM GREGORY. 

 University of Edinburgh, 



March, 1847. 



ivi66978 



