PETROLEUM (BURNING OIL). 295 



40" C. ; obtained by distillation of petroleum so long as it yields 

 volatile compounds, then by oxidizing the residue in the open, and 

 filtering through animal charcoal. 



Petroleum Oil or Burning Oil. — Petroleum oil or burning oil is 

 that t'ractioa from crude petroleum which is most used against insects 

 which ravage plants. It is used as such, or in different emulsions. 



Action of Petroleum on Plants. — Petroleum is very injurious 

 to plants. Spraying with petroleum emulsions is almost always pre- 

 judicial to the leaves and tender branches. The poisonous capacity 

 of petroleums of different compositions differ (Trott). The sensibility 

 of different plants is different ; whilst the cabbage stands a 5 per cent 

 emulsion, the vine only bears 2-5 per cent, and even that injures the 

 cucurbitacese. The action of emulsions depends greatly on their 

 preparation; perfect emulsions diffused through much water do not 

 separate drops of petroleum, that is to say, which do not split up have 

 a comparatively harmless action on the leaves of plants, whilst badly 

 prepared emulsions, allowing the petroleum to aggregate on the same 

 point, are in equal doses very injurious. In using petroleum to 

 destroy insects only perfect emulsions must be used. The prolonged 

 contact of petroleum on the trunk of a tree may become deadly and 

 must be avoided. The trunk and the branches coated, even in 

 winter, absorb suiftcient quantities of petroleum, which if they do not 

 cause the death of the tree, at least so far disturb its economy as to 

 retard the opening of the buds in the spring. Roots are likewise 

 very sensitive, and the absorption of petroleum through them causes 

 the death of the plant ; 20 cubic centimetres of petroleum spread in 

 4 litres of soil kill the vine, haricots, and weeds, such as Senecio and 

 Sondms. A soil di-enched with petroleum is no longer fertile, until 

 the petroleum is evaporated, but then there is produced, as after treat- 

 ment with carbon disulphide, a more intense vegetation resulting from 

 the perfect disinfection of the soil by petroleum vapours. Withelm 

 recommends steeping seed which it is desired to protect against 

 insects sixteen to twenty-four hours in pure petroleum. This pro- 

 longed contact only slightly lowers the germinative capacity of the seed. 



Action of Petroleum on Insects. — Petroleum acts on insects by 

 contact, and by its asphyxiating vapours. Contact with pure petroleum 

 causes the immediate death of all insects it is capable of penetrating, 

 even those with the hardest shells, and protects them from the insecti- 

 cides in aqueous solution. As an emulsion, petroleum is less energetic ; 

 eggs especially resist emulsions containing up to 30-35 per cent of 

 petroleum (Smith, Lintner, Forbes), whilst 2-5-6 per cent emulsions 

 kill all soft-skinned insects. The poisonous action of petroleum 

 vapour never manifests itself in the open air, only in a closed vessel, 

 or in the soil. In a closed vessel, Mouillefert destroyed the phylloxera 

 by placing a contaminated root for two days in a 2-litre vessel con- 

 taining at the bottom 5 cubic centimetres of petroleum. In the soil 

 the injurious action does not occur, except at a short distance from 

 the spot where the petroleum has been injected. From this point of 

 view, petroleum is inferior to carbon disulphide and cannot replace it. 



Use. — Burning oil has found the most varied applications in the 



