On the Composition of Waters of Land-Drainage. 147 



of soda, explain in a <freat measure the more powerful effect of 

 the latter on vegetation. During the active spring growth 

 of cereal crops dressed with nitrate of soda it appears that a 

 consideraljle excess of soluble nitrogenous food circulates in the 

 land, whilst no such excess is found in it at that period when 

 the crop is manured with ammonia-salts instead of nitrate of 

 soda. For this reason the effect of nitrate of soda upon a crop 

 of wheat is seen almost directly after a good shower of rain has 

 washed a top-dressing of nitrate of soda into the soil, and its 

 growth is much more rapid than it is when the crop is manured 

 in spring with ammoniacal fertilizers. 



5. All the drainage-waters collected in ^lay contained but 

 little potash, and as, upon most of the plots, considerable quan- 

 tities of sulphate of potash had been used, I found in these analyses 

 a full confirmation of the well-known fact that the soil has the 

 power of absorbing and retaining potash. 



6. On the other hand, the proportion of soda in the drainage, 

 it Avill be seen, is larger on the plots which were dressed with 

 nitrate or with sulphate of soda. Thus, Avhilst the drainage of the 

 unmanured Plots 3 and 4 contained only "35 of soda, that from 

 Plot 9 (nitrate of soda) contained 3*80 grains, and the drainage 

 from Plot 12 (sulphate of soda) 1*60, or considerably more than 

 all the other samples. Whereas the variations in the proportions 

 of potash in the different samples were but slight, and the 

 actual amounts of potash small, the variations in the relative 

 proportions of soda in the different samples were great, and the 

 actual quantities considerable, in the drainage from the plots 

 manured with soda-salts, thus showing a marked difference in 

 the retentive powers of soils for potash and soda. 



7. In three instances the amount of phosphoric acid was deter- 

 mined. The quantity of phosphoric acid in drainage-water, it 

 will be seen, amounts to mere fractions of a grain per gallon, 

 showing that soils have the power of absorbing and retaining 

 soluble phosphoric acid, which has been applied to them in the 

 shape of superphosphate or other readily soluble phosphates. 



I may observe, that as the quantity of phosphoric acid in 

 waters of land-drainage is very minute, it was necessary to 

 evaporate to dryness as much as half a gallon of water for each 

 determination. The phosphoric acid was determined in the 

 residue by the molybdate of ammonia process, and weighed as 

 phosphate of magnesia. 



8. The proportions of lime and sulphuric acid, it will be seen, 

 were much greater in some samples than in others ; as a rule, the 

 greater the proportion of lime, the more sulphuric acid occurred 

 in the water at the same time. 



The larger proportion of sulphate of lime in some of the 



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