754 



the waste water from wire factories usually eontains iron sulfate. Besides 

 this, the use of ferrous sulfate as a disinfectant in cesspools should also be 

 taken into consideration. Large amounts of iron sulfid are thus produced 

 which, through oxidation in the air, are transformed into iron sulfate and 

 sulfurous iron oxid. 



The ferrous oxid, like zinc from zinc sulfate, is retained by the soil and 

 changed to ferric oxid^ while a corresponding quantity of other bases, such 

 as calcium, magnesium, and potassium, combine with the sulfuric acid and 

 arc easily washed away. This impoverishment of the soil is accompanied by 

 an increase of magnetic oxid which initiates a souring and choking of the 

 ground. As soon as the bases for the transformation of the iron sulfate are 

 exhausted, the ferrous sulfate remains untransposcd, or appears also as free 

 sulfuric acid. 



However useful small amounts may be on rich soils (up to 150 kg. per 

 hectare, according to Konig^), since the sulfuric acid, thus set free, must act 

 as a loosening medium, just as injurious will be a continued addition of iron 

 sulfate with constant irrigation of pastures. Experiments show that if acid 

 compounds are given the plants instead of the basic salts which alone favor 

 their growth (iron sulfate is strongly acid) a deterioration of the hay results 

 and a decrease in the yield of milk. The different clovers and sweet grasses 

 (possibly with the exception of Glyceria flidtans) disappear gradually from 

 such pastures and sour grasses, the horsetails (Equisetum) and mosses take 

 possession of the soil. An addition of lime water causes the elimination of 

 ferrous hydroxid with the formation of gypsum and it will thus be possible 

 to purify waste water containing iron sulfate by the use of calcium. 



Waste Water Containing Copper Sulfate and Copper Nitrate. 



Waste water from silver factories and brass foundries is concerned 

 here. An insight into the composition of such water is given by an analysis 

 of solutions flowing from a brass foundry published by Haselhoff-. He 

 found in one liter : 



Copper sulfate, 51.619 g ; Copper nitrate, 5.298 g ; Zinc sulfate, 14.045 g ; 

 Ferrous sulfate, 2.422 g; Calcium sulfate, 1.943 g; Magnesum sulfate, 

 0.459 g; and free Sulfuric acid (SO;;), 30,376 g. This is, at any rate, a- 

 very extreme case, for it is one hundred times greater in the individual 

 elements than is the content of the water which flows from copper works 

 and silver factories. For the nature of the injury, however, the amount of 

 the elements is unimportant, since small quantities produce the same effect 

 when used in continual irrigation. The way in which the sulfate and nitrate 

 of the copper salts act on the soil is the same as with zinc and iron salts. 

 Copper oxid is retained in the soil and remains chiefly in the upper surface 

 of the pasture land. The sulfuric acid, which is set free, combines with the 

 calcium, magnesium, and potassium, and these salts, with irrigation, pass 



1 Denkschriit, p. 175. 



- Haselhoff, Landwirtsch. Juhrb. 1892, p. 263 and 1893, p. 848. Denksch., p. 176. 



