138 CHEMICAL MANURES. 



which do not dispense with passing the manure through Carr's 

 disintegrator. 



Basis on lohich Superphosphates are Sold} — In the beginning of 

 the superphosphate industry, superphosphates were sold according 

 to their percentage of phosphate of Hme sokible in water. But 

 there were disputes between buyers and sellers, the former not 

 finding the strength given them by the latter. A portion of the 

 phosphate had become insoluble on delivery. The British were the 

 first to determine that that part of the phosphate originally soluble 

 in water, and at the end of a certain time was no longer so, was, 

 however, soluble in weak reagents, such as carbonate of soda or oxa- 

 late of ammonia, whilst the phosphate, originally insoluble, did not 

 dissolve appreciably in these reagents. At first it was thought that 

 this phosphate which British chemists called " reduced " phosphate, 

 but now termed retrograde phosphate, was formed by the action 

 of the monocalcic phosphate on the tricalcic phosphate producing 

 an intermediate bicalcic phosphate. Such, at least, was the current 

 explanation fifteen years ago. Be that as it may, manufacturers 

 have got over the difliculty, not by improving their manufacture, 

 but in altering the basis of sale of superphosphates, i.e. by selling 

 them according to their content per cent of phosphoric acid soluble 

 in cold alkaline ammonium citrate which they term assimilable 

 phosphoric acid. This method of sale is evidently very convenient 

 for the manufacturer, and enables the works chemist to cease from 

 worrying over retrogradation whether it arise from bad manufac- 

 ture or the presence of impurities in the raw phosphates. 



Now, as Mr. J. Joffre observes : " When a superphosphate is 

 treated with citrate of ammonia in analysing it, both the citrate 



^ A 25 per cent soluble phosphate, say phosphoric acid = ll'4o per cent, is 

 the current British make of soluble phosphate. A 12 per cent Somme will give 

 a 30 per cent soluble phosphate which will bear an addition of 3 cwt. of 

 gypsum to the ton to bring it down to 25 per cent if the superphosphate is 

 dispatched as soon as made. Or the gypsum may be partially replaced by 

 a little Belgian phosphate. But in Britain it is not considered good business 

 policy to add a nitrogenous mnnure like bone dust to a superphosphate, and the 

 tendency of the workmen is always to use far more bone dust than that in the 

 formula, for reasons which will be readily appreciated ; the result being that 

 ^vhen it comes to stocktaking the leakage of bone meal and bone dust is exces- 

 sively large. What the translator cannot understand is the magical effect of 

 1-0 per cent of bone dust, say one-fifth of a cwt., i.e. 22 lb. to the ton. If the 

 superphosphate was very damp such a pinch of bone meal would be a drop in 

 the ocean ; 3 per cent of raw Gaf sa phosphate can be understood. It will 

 readily be seen that only by strict book-keeping by double entry can the amount 

 •of phosphate and bone dust used as driers be conU'oUed. The translator fears 

 the author is somewhat over-sanguine as to the efficacy of some of the drying- 

 machines and grinding machines which he describes. It appears to the former 

 that if a manure will dry naturally, as it should do, these machines are not so 

 indispensable as would be inferred, and where the manure will not dry naturally 

 one may be pardoned from doubting if the machines are quite so efficacious as 

 one is led to believe. — Tr. 



