114 INSECTICIDES, FUNGICIDES, AND WEED KILLERS. 



and the sulphuretted hydrogen given off by their decomposition, this 

 gas being for insects almost as poisonous as prussic acid. It is, more- 

 over, asserted in medicine that sulphides used in 5-20 per cent solution 

 in skin diseases, such as itch, act on the parasites by the sulphuretted 

 hydrogen formed in contact with the organic acids of the transpiration 

 and the carbonic acid of the air. 



Use against Bacteria. — Sulphides retard putrefaction and kill 

 microbes (Amsler). It has been tried to utilize this property to 

 treat plant diseases of bacterian origin, such as potato scab. The 

 bacteria which causes this disease of the potato is found, according to 

 Bolley, in the living tissues of the periphery of the tubers and never 

 penetrates deeply; it is aerobic. Bolley has submitted tubers so 

 attacked for twelve hours to the action of a 0"3-0"4 per cent 

 solution of potassium sulphide before planting them. At that strength 

 the causticity of the sulphide is not sufficient to injure the tubers. An 

 appreciable effect was obtained, but the sulphide has not the radical 

 effect of mercury bichloride. The results obtained by the sulphide are 

 still defective — 5 per cent of healthy tubers against 1 per cent in a 

 blank field. 



Gum Disease of the Olive (Mai di Gomma of the Italians). — Swingle 

 and Weber advise to combat this disease by potassium sulphide : 18 

 kilogrammes (39 "6 lb.) of potassium sulphide are dissolved in 15 litres 

 (3-3 gallons) of water; to this paste 12 kilogrammes (26-4 lb.) of 98 per 

 cent caustic soda are added and energetically stirred. The mass 

 heats, boils, and melts. As soon as boiling is over the bulk is made 

 up to 100 litres (22 gallons) with water. The cankers and wounds 

 formed by the disease are cleaned, diluted before use with an equal 

 bulk of water ; the roots, even sound ones, are stripped and watered with 

 a solution of this sulphide in 10 parts of water. 



Use against Fungi. — Pickling of Seed=Corn. — Dilute solutions 

 of potassium sulphide prevent the growth of fungi and their spores and 

 may kill them if of a certain strength. The action of the sulphide is 

 not the same on all spores, e.g. it is almost nil on the spores of 

 Phijtophthora Phaseoli, Taxter. (Lima bean mildew). Hitchcock 

 and Carleton remarked that a 1 per cent solution not only did not 

 destroy the uredospores of Pucciyiia graminis, Pers. (black rust) and 

 Puccinia coronata, Corda (coronated rust of oats), but rather acceler- 

 ated their germination. By numerous experiments on rusts Gallo- 

 way came to the same conclusion. The disinfection of grain in 0'75 

 per cent solution made no diminution in the rust. By spraying 

 winter wheat no appreciable result was obtained unless spraying 

 with a 0'5 per cent solution was repeated every ten days. Under 

 such conditions he obtained 1 diseased plant against 24 in the blank 

 plot. If twenty days' interval occurred between the sprayings the rust 

 did not diminish but the harvest was a little better. Kellermann and 

 Swingle were the first to observe the sensitiveness of the spores of 

 smut to sulphide, especially the loose smut of oats. Jensen tried if 

 grain could not be disinfected by sulphide against smut. The results 

 which he obtained were surprising, and he did not hesitate to advise it 

 in place of steeping in hot water recommended by him some years 



