354 INSECTICIDES, FUNGICIDES, AND WEED KILLERS. 



is killed by an emulsion containing 2 per cent of nitrobenzene ; but of 

 that strength the insecticide is prejudicial to the vines (Zechina and 

 Silva). Dufour also found that the maximum strength of a soap 

 emulsion of nitrobenzene should be 2 per cent nitrobenzene and 3 per 

 cent of soft soap. 



Schizoneura lanigcra, Hausm. (woolly aphis). — Nitrobenzene 

 enters into the composition of an insecticide made in Switzerland, 

 " Knadolin," invented by Kraft and recognized by the Federal Depart- 

 ment of Agriculture for the destruction of the woolly aphis. It con- 

 sists of 2 lb. of nitrobenzene, 1 lb. of potassium xanthogenate, 40 lb. 

 of soft soap, and 60 lb. of amyl alcohol. It is not used in the com- 

 mercial condition but in aqueous solutions. With 1 lb. of Knadolin 

 one can, according to the effect desired, prepare 1-4 gallons of liquid 

 insecticide. It immediately moistens all the substances which it 

 touches, which renders it superfluous to clean the trunk mechanically 

 previously. To make sure of killing well-hidden insects, it is well, 

 against colonies of woolly aphis, to use the insecticide only diluted 

 with fifteen times its volume of water. Goethe remarks that Knadolin 

 does not attack the shoots and leaves of trees like sapocarbol and lysol. 



PJii/lloxera vastatrix, Planch, (phylloxera of the vine). — Papasogli 

 recommends a mixture of 5 lb. of nitrobenzene, 5 lb. of sulphuric acid, 

 9 gallons of water, for the destruction of this plant louse (1876-1880). 

 The mixture is run into channels 8 inches deep between the stocks, 

 and closed up forthwith. 



Cochineals of the Olive-tree. — Mottareale advises for their des- 

 truction an emulsion which he regards as very efficient, consisting of 

 nitrobenzene 0-25-0-5 per cent, soft soap 0-2o-0-5 per cent, water 

 99-50-99-75 per cent. 



132. Carbolic Acid, C,.H.OH. — Preparation. — Carbolic acid or 

 phenol is obtained from coal tar, in which it is present to the extent of 

 3-12 per cent. When tar is heated carbolic acid distils, at the same 

 time as middle oils, between 150° and 200° C. Strong caustic soda is 

 -added to these oils, in which carbolic acid and its homologues dissolve. 

 The liquid is treated by five times its weight of hot water ; the phenols 

 -dissolve in the water, whilst the hydrocarbides remain insoluble. To 

 •obtain carbolic acid it suffices to treat this liquor by dilute sulphuric 

 .acid, and to decant. Crude carbolic acid, containing its homologues, 

 is thus obtained. To purify it, it is washed with water, dried, then 

 •distilled in cast-iron retorts, collecting the portion which passes beween 

 180° C. and 190° C, and crystallizing. Eectification is not required 

 in the case of carbolic acid used as an insecticide, for the homologues 

 of carbolic acid are as insecticidal as itself. 



Properties. — Carbolic acid is a solid body, colourless in the pure 

 state, crystallizing in long needles. The slightest trace of water lique- 

 fies it. It is soluble in twenty times its weight of water, and volatile 

 at the ordinary temperature. It possesses a special odour and a burn- 

 ing taste. Carbolic acid is a powerful antiseptic, but it is also poisonous 

 and caustic. It coagulates albumens. 



Action on Plants. — Injurious. — Nessler has shown that young 

 plants die if an amount of carbolic acid more than 0*012 per cent be 



