740 



manifested. This is shown in Wislicenus' experiments with the soot from 

 hard coal, Ugnite and benzine, as well as extracts from soot, by means of 

 which the leaves of the hornbean and linden and later also spruce needles 

 were slightly etched. Probably, as they dry up, the salts effect an osmotic 

 removal of w^ater and a drying of the cells. The same experiments also dis- 

 pelled the fear that a thick coating of soot absorbs the light, changing it into 

 heat and, therefore, acting disadvantageously. 



It is theoretically possible that the carbon dio.vid carried in the smoke 

 can act injuriously for even experiments with an extreme increase of this 

 gas above the normal 0.04 to 0.06 per cent, have proved the retardation of 

 assimilation but this can scarcely be spoken of in practical industry. The 

 same holds good for carbonic oxid. 



The metallic elements of the smoke from smelters (see table) also enter 

 into the question of the effect of fllying ashes. According to Freytag's inves- 

 tigations\ pure metallic oxids are usually non-injurious. Naturally, foliage 

 bearing such oxids cannot be used as food for animals, since they may easily 

 cause inflammator}- diseases. 



Also, these metallic elements such as insoluble oxids or carbonates and 

 silicates scarcely injure the aerial parts of the plants more than does the 

 street dust. Soluble compounds, on the other hand, such as arsenous acids, 

 sulfates, and chlorides {copper, zinc, and lead) are principally concerned 

 here and produce brown spots through the corrosion of the tissue, as soon as 

 they are deposited on moist leaves. They are said not to injure dry foliage 

 and a subsequent wetting from rain easily washes away the coating. Mer- 

 cury fumes in the air always act very injuriously. The compounds washed 

 into the soil by rain are absorbed by it and are usually non-injurious. A 

 large accumulation of arsenic (more than o.i per cent.) is disadvantageous. 

 Experiments made by Phillips- prove that healthy plants undergo no dis- 

 turbances in growth from the taking up of lead and zinc, while copper acts 

 as poisonously as arsenic and disturbs the root development. Klein-' and 

 numerous, more recent observers furnish proof of the presence of arsenous 

 acids in plants. Such poisoning of the soil may occur, for example, near 

 copper smelters and in the litigation against the Manns feld-Hettstadter 

 copper smelters Grouven refers especially to this point*. My own experi- 

 ence in the same region shows that, at present, large surfaces of the fields 

 have become poisoned and, despite very abundant fertilization, yield very 

 meager harvests. The experiments in which soil which had become unfer- 

 tile was carried from the vicinity of copper works to a region free from 

 smoke prove that the gases in the smoke are not alone the injurious factors. 



1 Freytag, in .Tahrb. fiir da.s BeiK- und Huttenwesen im Kclnigieich Sachsen 

 1S73, pp. 24 and 36, cit. in Hasenclever. — Landwirtsch. Jahrb. 1S82, p. 315-375. In 

 regard to the action of smoke, the author differs from Schroder inasmuch as he does 

 not consider the sulfurous acid as such to be the injurious agent, but only the sul- 

 furic acid which is being formed from it. 



- Phillips. The absorption of Metallic Oxides by plants; cit. Bot. Centralbl. 

 1883, Vol. XIII, No. 11, p. 364. 



3 Chemischer Ackersmann, 1875, Pai't 4. 



4 Fuhling's neue landwirtsch. Z. 1871, Part 7, p. 534. 



