214 Composition and Value of Guano. 



that 4 lbs. of common salt would furnish all the soda of 100 lbs. 

 of ^uano, we shall not be far from the mark. 



This quantity in a ton of guano would amount to about 90 lbs., 

 or a little more than | cwt. ; since common salt may be in most 

 places bought for SOs. a ton or less, the sum of is. 3c?. is quite 

 enough to allow for all the soda compounds in a ton of Peruvian 

 guano. 



These two items, of 25. for gypsum and \s. Sd. for common salt, 

 constitute the entire addition which requires to be made to the 

 value of the three staple ingredients. 



Small though the sums are, it is very fair to take account of 

 them in comparing guano with other manures ; but it would be 

 absurd to allow them to complicate the present discussion. 



Having disposed of all other claims to our attention, we will 

 now endeavour to ascertain the relative value of the principal 

 ingredients of guano. It will be obvious that we must look 

 beyond guano itself for any help in this undertaking; for al- 

 though eventually it may be very interesting to observe how 

 far its selling price approaches to the united average value of 

 its constituents, it would be manifestly impossible without external 

 evidence to affix to each of these a fair share of pecuniary im- 

 portance. It is to external evidence that we must first look for 

 a decision of this particular. 



It may probably be convenient to begin with phosphate of lime, 

 for it has been shown that the earthy phosphates so frequently 

 mentioned almost entirely consist of this substance. 



In addition to Peruvian guano itself, there are three principal 

 sources of phosphate of lime available for agricultural employ- 

 ment — 



Bones in their various states ; 



The mineral phosphates known as coprolites ; 



And the lower priced guanos, such as the Saldanha Bay and 

 Patagonian varieties. 



It seems odd to draw any argument from the last source, par- 

 ticularly as the supply of phosphatic guano has well nigh ceased, 

 but some assistance may be derived from such a proceeding. 

 Whilst, however, we are discussing the relative economy of phos- 

 phate of lime obtained from different sources, it must never be 

 forgotten that phosphate of lime, agriculturally considered, is not 

 always, if we may so speak, phosphate of lime ; that is to say, it 

 may in one case be very different in its action on vegetation to 

 what it is in another, dependent upon the extent of its solubility 

 and other circumstances. In putting a price upon the earthy 

 phosphates of guano, we must select for our guidance that source 

 of phosphate of lime which exhibits the nearest resemblance in 

 these essential particulars. For reasons which will presently be 



