120 INSECTICIDES, FUNGICIDES, AND WEED KILLERS. 



a 5 per cent dose. To succeed, the dose used must be considerable ; 

 instead of using pure sulphate, the double salts from the mines, kainite 

 or carnallite are used, but these are less active than the pure salts. 

 Hollrung has observed that in big doses these salts are unfavourable 

 to the formation of sugar in the beet. There are no great advantages 

 in using potassium chloride or sulphate in massive doses to remedy 

 the exhaustion of the land, for the effect is somewhat illusory. This 

 practice has moreover been abandoned since, as the outcome of Aime 

 Gerard's researches, arable land may be sterilized by large doses of 

 carbon disulphide. 



Agriotes lineatus, L. (striped wire-v?orm). — Comstock and Slinger- 

 land ascribe insecticide properties to potassium sulphate against the 

 adults. Smith regards a 12 per cent solution of kainite as an excellent 

 insecticide. But Marlatt, who used big doses of kainite, against wire- 

 worm (Elaterides, click beetles), got no appreciable result. Mineral 

 manures such as potash salts injure certain parasitic larvae, e.g. : — 



Lachnoster'na fusca, Frohl (May beetle) ; Lachnosterna arctiata. — 

 Chittenden found kainite very active. Possibly the larvae of the 

 Elaterides which are very mobile flee from soils which have been 

 treated with big doses of potash manures. Opinions are too contra- 

 dictory to admit that potash salts kill them. 



Atjrotis sec/etmn, W. V. (common dart moth). — The grey worm, 

 the caterpillar of this butterfly, is driven off" or destroyed by watering 

 the infested spots by a 12 per cent solution of kainite. 



Jassiis sexnotatUH, Fall. — Steglich uses kainite in a composition to 

 combat this grasshopper: kainite 10 lb., carbolic acid 1 lb., soft soap 

 10 lb., in 100 gallons of water. 



Snails. — Kainite is a specific against snails (Taschenberg). 



3S. Nitrate of Potash, KNO^. — Occurrence. — Nitrate of potash, 

 or saltpetre, occurs in nature ; it is found in the great plains of China, 

 India, and P^gypt. It is extracted by removing the nitrated earth for 

 a few centimetres and lixiviating it. The liquor is then run into large 

 basins and evaporated in the sun. 



Preparation on the Large Scale. — By double decomposition of 

 sodium nitrate and potassium chloride. By hot concentration of the 

 solution the sodium chloride formed crystallizes, whilst the saltpetre, 

 much more soluble when hot than common salt, remains in solution 

 and does not deposit until after cooling. 



Properties. — Saltpetre is very soluble in water, 10 gallons of water 

 dissolve 15 lb. of saltpetre at 9° C, 85 lb. at 15° C, 246 lb. at 100° C. 

 (212" F.), 335 lb. at 118° C. At a great heat [igneous fusion] salt- 

 petre is a powerful oxidizing agent. 



Action on Plants. — Potassium nitrate like potassium chloride is 

 a plant food, and what has been said anent potash salts applies to 

 potassium nitrate.' Concentrated solutions injure plants. 



Action on Fungi and their Spores. — Wuthrich's researches on 

 the action of metallic salts on the spores of fungi also include potassium 



' Translator's Note. — But the nitric acid is the predominating agent of potas- 

 sium nitrate, and as a plant food pats it beyond comparison with other potash salti?,. 

 the phosphate excepted. 



