Composition and Value of Guano. 213 



establish a standard value for each of these — and, having done so, 

 to apply it to the composition of Peruvian guano. It is hoped 

 that, independently of the specific purpose to which it is directed, 

 this inquiry may not in itself be devoid of interest to the agricul- 

 tural reader. 



It has been stated more than once in the course of this paper 

 that the ammonia, the earthy phosphates, and the mineral alkali, 

 potash, are the only iviportant ingredients in guano. I say im- 

 portant, because, without denying the use of sulphate of lime and 

 of common salt as agents of vegetation, I am prepared to show 

 that the cost of their separate purchase is so trifling as to prevent 

 us from attaching any considerable pecuniary value to the small 

 quantities of these substances existing in guano. 



The present is the proper place to discuss this point ; and by 

 eliminating from the question those minor details which will not 

 materially influence the general results, the inquiry will be greatly 

 simplified. 



After setting aside the ammonia (present or to come), the 

 earthy phosphates, and the potash, what else is there in guano 

 deserving of our attention? Referring to Table, No. 1, we find 

 mention made of '' water and sand," — these are ingredients of no 

 value ; again, of " magnesia and oxide of iron," — but in quantity 

 inconsiderable; and also of "^sulphuric acid," — but in no case 

 exceeding 4J per cent., and giving us in 8 cases a mean of 3*82 

 per cent. 



A ton of guano will, therefore, contain on an average 85J lbs. 

 of sulphuric acid ; a quantity which would be supplied by about 

 185 lbs. of gypsum. Gypsum can be bought in any quantity at 

 15a*. or 2O5. a ton.* Assuming the latter as a fair price, and that 

 1 ton of Peruvian guano contains on an average sulphuric acid 

 equal to 1| cwt. of gypsum ; then the outside allowance which 

 we can make for this ingredient is Is. Sd. or 2s. in a ton of the 

 guano. 



It has been before stated upon what grounds we have adopted 

 this principle of calculating the value of each ingredient according 

 to the cheapest form in which it can be supplied. 



Upon reference to the Table we find the alkali soda existing 

 partly as common salt and partly in other forms of combination. 



The mean per centage of common salt is . 1*82 

 And of soda in its other salts . . . 1 • 14 



If we assume that on an average in Peruvian guano this alkali 

 occurs to the extent of 4 per cent, of common salt, that is to say, 



* The price of native gypsum is, I believe, somewhat higher than that above stated. 

 The calculations above rather refer to sulphate of lime, which, as a refuse product in the 

 manufacture of tartaric acid, stearine candles, &c., may be had in abundance at the 

 price named. 



