On Guano. 



305 



have no doubt. At present the farm-yad manure takes the lead ; the 

 guano is next ; but the crop on the nitrate is by no means making the 

 same progress. 



" I have tried the guano on several other crops, in different propor- 

 tions, and all prove very much in favour of its being a most valuable 

 manure ; and the produce from it, as in the case of farm-yard manure, 

 will be in proporcion to the quantity laid on — at least, as far as 8 cwt. 

 to the acre : beyond that, I fear, it would be too powerful for any 

 crop." * 



These are all the experiments of which the results have been 

 transmitted to me. Though they leave very much to be desired, 

 yet they are sufficient to show — that in the climate and on the soils 

 of England the guano is fitted to promote vegetable growth nearly 

 as much as on the arid plains of Peru. 



§ 4. Chemical Composition of Guano. 



To what cause are we to ascribe this extraordinary effect of 

 guano in fertilising and increasing the produce of the land ? 

 What does it contain that renders it so grateful to vegetable life ? 

 We know that pigeons' dung and the liquid manure of the farm- 

 yard act upon vegetation almost^ if not quite, as efficiently as the 

 guano ; and as this latter substance has precisely a similar origin, 

 we can in some measure understand from analogy only, why it 

 should be so useful as a manure. A clear comprehension, how- 

 ever, of the kind and extent of its action on vegetable life, and of 

 the circumstances under which it is likely to be most beneficial^ 

 can only be obtained from the study of its chemical constitution. 



The first analysis of this substance was, I believe, published by 

 Klaproth (Beitrage, Th. iv. p. 299) ; the specimen having been 

 furnished to him by Humboldt. He found it to consist of — 





Per Cent. 



Urate of ammonia ..... 



16 





Phosphate of lime ..... 



10 





Oxalate of lime ..... 



12 



75 



Silica ....... 



4 





Common salt ...... 



0 



5 



Sand ....... 



28 





Water and other organic and combustible matter 



28 



75 



100 



* These experiments would have been much more valuable had the 

 results been given in the state of d?'y hay instead of that of green grass. 

 The reason of this is, that different samples of grass from the same field 

 yield often very different proportions of dry hay. Thus 100 stones of grass, 

 cut from each of six different half-acres — treated with different manures — 

 in the same field, near Aske Hall, Richmond, gave respectively of dry hay 

 52, 53, 36, 46, 40, and 36 stones. No accurate conclusion therefore can be 

 drawn from the weights of the green grass yielded by the several parts of a 

 field. 



VOL. II. 



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