§ 72. Influence of Hydrochloric Acid on Vegetation.—Hydrochloric acid fumes, if emitted from works on a large scale, injure vegetation much. In former years, before any legal obligations were placed upon manufacturers for the condensing of the volatile products, the nuisance from this cause was great. In 1823, the duty on salt being repealed by the Government, an extraordinary impetus was given to the manufacture of hydrochloric acid, and since all the volatile products at that time escaped through short chimneys into the air, a considerable area of land round the works was rendered quite unfit for growing plants. The present law on the subject is, that the maximum quantity of acid escaping shall not exceed 2 grains per cubic foot of the air, smoke, or chimney gases; and, according to the reports of the alkali inspectors, the condensation by the improved appliances is well within the Act, and about as perfect as can be devised.
It appears from the reports of the Belgian Commission in 1855, when virtually no precautions were taken, that the gases are liable to injure vegetation to the extent of 2000 metres (2187 yards) around any active works; the more watery vapour the air contains, the quicker is the gas precipitated and carried to the earth. If the action of the vapour is considerable, the leaves of plants dry and wither; the chlorophyll becomes modified, and no longer gives the normal spectrum, while a thickening of the rind of trees has also been noticed. The cereals suffer much; they increase in stalk, but produce little grain. The leguminosæ become spotted, and have an air of dryness and want of vigour; while the potato, among plants utilised for food, appears to have the strongest resistance. Vines are very sensitive to the gas. Among trees, the alder seems most sensitive; then come fruit-trees, and last, the hardy forest-trees—the poplar, the ash, the lime, the elm, the maple, the birch, and the oak.[92]
[92] Those who desire to study more closely the effect of acids generally on vegetation may consult the various papers of the alkali inspectors contained in the Local Government Reports. See also Schubarth, Die saueren Gase, welche Schwefelsäure- und Soda-Fabriken verbreiten. Verhandlungen des Vereins zur Beförderung des Gewerbefleisses in Preussen, 1857, S. 135. Dingler’s Journal, Bd. 145, S. 374-427.
Christel, Ueber die Einwirkung von Säuren-Dämpfen auf die Vegetation.
Arch. f. Pharmacie, 1871, p. 252.
Vierteljahrsschrift für gerichtliche Medicin, 17 Bd. S. 404, 1872.
§ 73. Action upon Cloth and Manufactured Articles.—On black cloth the acid produces a green stain, which is not moist and shows no corrosion. On most matters the stain is more or less reddish; after a little time no free acid may be detected, by simply moistening the spot; but if the stain is cut out and boiled with water, there may be some evidence of free acid. The absence of moisture and corrosion distinguishes the stain from that produced by sulphuric acid.