On Superphosphate of Lime. 



221 



Peroxide of iron . . . . . . .6*47 



Magnesia . . . . . . . .1-08 



Chloride of sodium 0*08 



Soda 0-20 



Potash 0-25 



Sulphuric acid ....... trace. 



•Fluorine and loss in analysis , . . .3*49 



100-00 



A mineral phosphate of this composition will be of somewhat 

 greater value as a source of phosphoric acid for superphosphate 

 than the coprolites of the crag. I shall not, however, attempt to 

 give a formula for its treatment by sulphuric acid, since it is quite 

 likely that further experience in the working of the beds may 

 lead to the discovery of continuous layers of a more uniform 

 character, and less intermixed with quartz and other extraneous 

 substances which reduce the proportion of phosphoric acid. 



After all, the practical question is not what percentage of 

 phosphate of lime is contained in a particular fragment of this or 

 that mineral, but what will be its average proportion on tens and 

 hundreds of tons ; and this information can only be satisfactorily 

 furnished after some considerable experience in the working of 

 the deposits. It is also for our agriculturists and manufacturers 

 of manure to remember that phosphoric acid and lime unite in 

 several proportions, forming compounds, all of which would be 

 included under the general head of "phosphate of lime*" but 

 their value as sources of superphosphate depends upon the actual 

 percentage of phosphoric acid and its relation to the quantity of 

 lime — hone-earth phosphate being in all cases the standard of 

 comparison. 



Superphosphate from Guano. — Whilst a good supply of guano, 

 rich in phosphate of lime, was to be met with in the market, this 

 substance was frequently resorted to for the production of super- 

 phosphate. Saldanha Bay guano contains, on an average, 56 per 

 cent., and Patagonian 44 per cent., of phosphate of lime, unmixed 

 with any quantity of carbonate. Peruvian guano contains usually 

 24 per cent. : it has not, that I am aware, been employed in any 

 quantity as the basis of superphosphate, but may with advantage 

 be added to the manure as a source of nitrogen or ammonia. It 

 would be well worth while also to try a mixture of Peruvian 

 guano with oil of vitriol as a manure for turnips. 



Substances employed as accessories to the manufacture of Super- 

 phosphate. — In treating any posphoric substances with sulphuric 

 acid it is usual to employ so much water that the product is semi- 

 fluid, or at all events so damp as to need the addition of some dry 

 absorbent material to bring it to a proper consistency for use : the 



