II 



laboratory experiment, that the greater part of the phosphoric 

 acid reverted in soils is in the form of iron and aluminum phos- 

 phates. On adding a solution of superphosphate to three repre- 

 sentative soils he found after several days that all the phosphoric 

 acid was soluble in ammonium citrate at a temperature of 65 

 degrees C. "This" the author states "shows that most of the 

 phosphoric acid was present in the form of iron and aluminum 

 phosphates, since tri-calcium phosphate is much less readily at- 

 tacked by this reagent than these phosphates." The author 

 criticizes results obtained by Albert and Vollbrecht 1 , from which 

 these investigators concluded that the phosphoric acid not dis- 

 solved by ammonium citrate at 40 degrees C had become insoluble 

 tri-calcium phosphate. Unfortunately Gladding did not give the 

 composition of the soils used in his experiments. 



The composition and action of superphosphate have been 

 studied from many points of view. Weilandt 2 found it to be very 

 completely absorbed by marl. The action was rapid. Marge- 

 stein 3 showed its value to be increased by mixing with wood 

 ashes. He grew potatoes, mustard, barley, and maize on a 

 diluvial sandy soil. Quantities of ashes up to 25 per cent were 

 beneficial. Analyses of soils used were not given. 



From his results Joffre 4 referred reversion to the formation 

 of phosphate of iron. He determined its coefficient of solubility 

 in water, in water charged with carbon dioxide, and in solutions 

 of different salts. In all cases it was less sensitive to these 

 substances than tri-calcium phosphate. Vegetation tests showed 

 it to be less valuable. 



Thompson 5 determined the absorptive power of sand, as well 

 as that of the same sand containing known quantities of ortho- 

 clase, calcium carbonate, iron and aluminum hydroxides, of 

 mixtures of calcium carbonate and orthoclase, and of calcium 

 carbonate and hydroxides of iron and aluminum. He also 

 noticed the effect of sodium chloride and potassium nitrate on 

 the process of absorption. The original publication was not 



1 Bied. Centr. 1880, 87. 



2 L,andw. Versuchs-Stat., 34, 207. 



3 Bied. Centr., 1888, 225. 



4 Bull. Soc. Chim., 47, 312. 



5 Inaug. Dissertation, Dorpat, 1890. 



