EXPERIMENTS OF LAWES AND -GILBERT. 299 



superphosphate and potash salts during a series of years. 

 But ill the first year they suppUed a plot of ground 

 for a whole series of years with the constituents of 

 corn and straw, phosphoric acid and silicate of potash 

 (560 lbs. of bone-earth rendered soluble by sulphuric 

 acid, and 220 lbs. of silicate of potash), and manured 

 it, in the follo^\dng years, mtli salts of ammonia only, 

 and they would have us to believe that the increased 

 crops obtained mider these circumstances were due to the 

 operation of salts of ammonia alone ! 



The imperfect nature of the experiments made by 

 Messrs. Lawes and Gilbert will appear, perhaps, more strik- 

 ing, if the question which they pretend to solve is stated 

 in another form. We will assume that the point to be 

 proved was, that the high additional crops, yielded by a 

 wheat field manured with guano, were due to the operation 

 of the salts of ammonia in the guano, and that its other 

 constituents had no share in the work. If the guano had 

 been hxiviated with water, and two portions of a field 

 had been manured, the one with guano, the other with 

 the soluble constituents of an equal quantity of guano, 

 only two cases could occur ; the crop of both plots would 

 be either equal or unequal. If the crops were equal, it 

 would be manifest that the insoluble constituents of the 

 guano had no effect : if the crop upon tlie plot manured 

 w^ith guano was greater, it would be certain that the 

 insoluble constituents (mineral constituents, as Messrs. 

 Lawes and Gilbert would term them) had some share in 

 producing the additional crop. The extent of this share 

 could perhaps be determined, if a third plot were 

 manured with the insoluble constituents, i. e. with the 

 ILxiviated residue of an equal quantity of guano. 



If an experimentalist, in carrying out his proof, in- 

 stead of following this method, had, on the contrary, 



