40 INSECTICIDES, FUNGICIDES, AND WEED KILLERS. 



for five minutes. Scalding carefully done with water at the tempera- 

 ture indicated is always eflicacious, and has no injurious action on 

 the vines if care be taken to perform it before the appearance of the 

 bud. It is recognized that of all the treatments adopted against the 

 Pyralis, scalding is still that which succeeds best. But it must be 

 carried out with a certain regularity each year, otherwise the butter- 

 fly would again appear. This is the treatment which succeeds best 

 against the Cochylis, provided it be done from October to November. 



Margantia histrionica, Hahu (the red cabbage bug). — Murfeld has 

 shown that these small bugs do not stand water heated to 65'5° C. 

 (150° F.), a heat which does not alter cabbage leaves. Cochineals also 

 suffer much from treatment with hot water. Eeh found that 

 genex'ally they did not stand a great heat. Water at 54° C. (129-2° F.) 

 kills them in forty minutes and water at 55° C. (131' F.) in twenty- 

 two minutes ; water at 60''-65° C. (140°-149° F.) kills the apple cochineal, 

 Aspidiotus ostreaforviis, and the pear cochineal, Diaspis piricola, but 

 most cochineal stand a greater heat. The scalding of trees in winter 

 is, /therefore, an excellent method of freeing them from all these 

 parasites. 



Tetranychus telarius, L. (red spider). — In November this acarus 

 takes refuge under the bark of the stock. The hot-water treatment 

 can then be applied. The scalding executed as described above to 

 destroy Pyralis can at the same time get rid of the red spider. 



2. Hydrogen Peroxide, H._,Oo. — Preparation. — By decomposing 

 barium peroxide by hydrochloric acid in the cold and then precipitat- 

 ing the baryta by sulphuric acid. 



BaOa + 2HC1 = BaCl, + H,0, 



Barium Hydro- Barium Hydrogen • . 



peroxide. chloric chloride. peroxide, 



acid. 



Projjerties. — Hydrogen peroxide is a colourless syrupy liquid. A 

 heat of 27°-30° C. (80"6°-86° F.) and light decompose it into water and 

 oxygen. Aqueous solutions are very unstable but a small amount of 

 sulphuric acid gives them stability. 



Use. — The numerous applications of hydrogen peroxide in human 

 medicine led to the expectation of good results in the treatment of 

 plant diseases with this product. Hitchcock and Carleton tried 

 hydrogen peroxide in solution of different strengths on the uredo- 

 spores of Puccinia, but a solution of — 



TABLE IX. — Result of Treating Puccinia Uredospores with Hydrogen Peroxide 

 of Various Strengths. 



0-1 per cent acting during 7 hours on spores of Puccinia graminis, Pers. 

 1-0 „ ,, „ 17 „ „ Puccinia Bubigo vera, Wint. 



3-0 „ ,, „ 14 ,, „ Puccinia coronata, Corda. 



far from destroying these spores rather favoured their development 

 than otherwise. 



