PHOSPHORUS FERTILIZERS 135 



Should any new uses for sulphuric acid arise, the situation 

 might be improved. Among possible new agricultural uses 

 may be named the destruction of weeds. 



Dr. Winifred Brenchley reports : " SULPHURIC ACID. 

 This is the most potent substance utilized for weed destruc- 

 tion, and owing to its corrosive nature needs very special 

 precautions in handling. If properly dealt with, however, 

 it proves effective in cases in which the more usual sprays 

 are of little value. Sulphuric acid is one of the few sprays 

 that has been found to clear grass land of bracken. A 5 % 

 solution causes the leaves to wilt within a few hours, and some 

 days later the stems turn black and wither, because the acid 

 is gradually conducted along the midrib and down the stalk, 

 eventually reaching almost to the underground rhizomes. 

 A new growth springs up later, but a second spraying disposes 

 of this for the year and also weakens the plant for the 

 future. Where the growth of bracken is dense the canopy 

 formed by the bracken leaves protects the underlying 

 herbage from the harmful effect of the acid, and as the 

 following year the fern is later in appearing the grasses are 

 able to get ahead earlier, resulting in an improved pasture. 



"On the Continent, sulphuric acid is considered a safe 

 spray for cereals if used when the crop has only about five 

 or six leaves. It is much used in parts of France (IyOt-et- 

 Garonne) for destroying wild radish among wheat, 90-100 galls, 

 per acre of an 8 or 10 % solution being employed. 

 It is somewhat selective in its action, as certain weeds 

 escape, especially wild oat (Avena fatua), medicks (Medicago 

 sp.) and members of the lily family (as wild onion). It is, 

 however, deadly to most annual and biennial weeds as 

 poppies, charlock, corn buttercup, cornflower, wild carrot, 

 radish, vetches and vetchlings, and it is said to be very 

 effective in clearing these pests from badly infested fields. 

 For general use 60-70 galls, per acre of a 10 solution 

 is sufficient for oats, rather less being used for barley." 



Grinding Rock Phosphates. The other raw materials 

 besides sulphuric acid that are used for the manufacture of 

 superphosphates are some of the various rock phosphates, 



