190 INSECTICIDES, FUNGICIDES, AND WEED KILLERS. 



contact be prolonged after nineteen hours the germination of the spores 

 becomes more difficult. 



Use. — Bust. — As a preventive against rust, Galloway tried bi- 

 chromate of potash. The seeds were immersed for twenty-four hours in 

 a 5 per cent solution of bichrome and the ground sown watered with 

 a, solution of the same strength. The use of the bichrome enabled him 

 to free the field from rust, but the yield was inferior to that on the check 

 plot infested with rust. Bichrome solutions act in as poisonous a 

 manner on the seeds as on the spores which contaminate them, and it 

 follows after this disinfection that the seeds do not spring up except 

 in small proportion. The watering of the sown ground is likewise 

 very prejudicial to the sprouting of the grain. 



Stinking Smut (bunt). — Kellermann and Swingle came to the same 

 conclusions as Galloway as to the action of bichrome on the spores of 

 fungi and on the grain of cereals. Although an immersion cf twenty 

 hours in a 5 per cent bichrome solution kills the spores of Tilletia 

 caries, Tul., the treatment cannot be utilized as the grains suffer too 

 much. 



Peronosjwra viticola, De By. (mildew of the vine). — Kaserer tried as 

 a substitute for bouillie bordelaise : (1) a mixture of 1 per cent of 

 bichromate and lime, (2) a mixture of 1 per cent of chrome alum and 

 lime; these two bouillies only gave absolutely negative results, but 

 whilst the bichromate of lime greatly damaged the leaves the hydrated 

 oxide of chromium did not injure them. 



Gonchylis ambignella, Hub. (cochylis). — Dufour tried against the 

 caterpillar of this butterfly a 3 per cent solution of bichrome, but he 

 found that it in no way disturbed the caterpillars, whilst it spoiled the 

 grapes. 



75. Permanganate of Potash, KMnO^. — Preparation. — By 

 heating in an iron crucible a mixture of 50 parts of manganese dioxide 

 with 50 parts of potassium chlorate and 60 parts of potash dissolved in 

 the smallest quantity of water. This mixture is gradually heated to 

 dull redness, then cooled and extracted with boiling water. A purple 

 liquid is thus obtained which crystallizes on evaporation in blackish 

 violet needles with metallic lustre. 



Properties. — Potassium permanganate dissolves in 15-16 parts of 

 cold water. It is a powerful oxidizing agent decomposing organic 

 matter in the cold. Owing to this property it acts as an energetic and 

 rapid disinfectant (Condy's fluid) ; its action is instantaneous, especially 

 la the presence of an acid. Weak permanganate solutions do not 

 keep in open vessels, and it is best to use these anticryptogamic solu- 

 tions immediately after their preparation. 



Action on Fungi. — The spores of fungi resist the action of this 

 oxidizing agent better than that of poisonous salts. Hitchcock and 

 Carleton found that the uredospores of the Paccinia graminis, Pers. 

 (linear rust) can germinate in a 1 per cent solution of permanganate 

 of potash. Arieti found that the dose required for the disinfection of 

 seed-corn was so strong that it killed the grain as well as the adherent 

 spores. It is otherwise with the mycelium of fungi. The tender 

 filaments of the mycelium are easily destroyed by permanganate solu- 



