298 INSECTICIDES, FUNGICIDES, AND WEED KILLERS. 



caterpillars of the common dart moth, the larvae of wire-worms, the 

 nematodes, and the larvye of the heet carrion beetle. It siiffices at the 

 time of tillini^ the ground to bury rags steeped in oil and petroleum 

 from the factories rather deeply underground. 



Gryllotalpa vulgaris (mole cricket). — Gemadius advises to destroy 

 the grasshopper by running petroleum into the tunnels which it bores 

 in the ground. A 25 per cent emulsion of petroleum is as effective 

 as pure petroleum. 



Culex pipiens (common gnat). — Two grammes of petroleum per 

 acre suffice to form on the surface of stagnant water a pellicular layer 

 which kills the gnats which live in the water. The larvae of the 

 common gnat, being amongst the number, it is easy to get rid of them, 



Lcpus europcBus, L. (hare) ; Lepus cuntculus (rabbit). — Taschenberg 

 points out the fact that trees treated by petroleum are respected by 

 hares and rabbits, and Hofer advises simply to stretch a cord steeped 

 in petroleum around the fields and gardens which it is desired to pro- 

 tect from these rodents. 



Use of Petroleum as Emulsions. — Petroleum is divided 

 mechanically into infinitely small particles by mixing it mechanically 

 with finely divided solid substances, sand, earth, or with liquids, 

 aqueous solutions, milk, or oil. The concentration and the com- 

 position of the emulsions vary greatly. Comparatively with pure 

 petroleum a well-prepared petroleum emulsion, that is to say, homo- 

 geneous, behaves in its effects on plants and insects like a dilute solu- 

 tion. According to the concentration of the emulsion its capacity for 

 injuring the plant as well as its insecticidal properties will be diminished 

 or increased. 



1. Petroleum mixed with Sand. — Perfect division of the petroleum 

 is obtained by mixing it with sand or earth as follows : Petroleum 

 1 litre, sand 4 litres (Ritzema Bos) ; petroleum 1 litre, sand 40 litres 

 (Husson). It is used especially when a small amount of petroleum 

 is to be spread over a large surface. The amounts given above suffice 

 for 25 square metres of soil, say 30 square yards. The action of the 

 petroleum in these conditions lasts ten to fifteen days. 



2. Petroleum Emulsion and Water. — Petroleum is insoluble in water 

 but it is capable of forming with it milky mixtures termed " emulsions," 

 which have the properties of a solution. It is, however, difficult to ob- 

 tain a perfect emulsion with these two bodies so different in density ; 

 even the special apparatus like that of Goff' accomplishes the end in view 

 with difficulty. Aqueous petroleum emulsions are very unstable, and 

 petroleum aggregates quickly to reform a layer on the surface of the 

 liquid. Petroleum and water emulsion is not perfect enough to allow 

 it to be used on the tender parts of plants, and it is now no longer 

 used except to disinfect trees in winter, to spread petroleum uniformly 

 over the fields, and to disinfect seed. Lossen designed a simultaneous 

 double jet of water and petroleum meeting with force in a common 

 space, and producing a perfect emulsion, but this emulsion likewise 

 dissociated on the surfaces touched, forming big drops of petroleum, 

 always injurious. 



3. Lime and Petroleum Emulsion. — Galloway recommends an 



