130 INSECTICIDES, FUNCtICIDES, AND WEED KILLERS. 



of its solutions on bacteria and ferments do not commence except at 

 the temperature at which this salt decomposes, and that it only there- 

 fore possesses the disinfectant action of carbon disulphide. But this 

 does not in any way detract from its valuable properties as an antiseptic, 

 since carbon disulphide acts on bacteria in aqueous solution at Oo per 

 cent and that this product contains 47 per cent of carbon disulphide. 

 In medicine xanthogenate of potassium has found different uses. 

 Lewin recommends it against helminthiasis and for different affections 

 of the skin. 



Use. — Xanthogenate of potassium may be used in all cases where 

 carbon disulphide and sulphocarbonate of potash have been found 

 useful. Its solubility in water is greater than that of carbon disulphide 

 and its stability in air more perfect than that of sulphocarbonate of 

 potassium. Its properties would have assured it a much higher place 

 in agricultural medicine if its price were not higher than similar com- 

 pounds. Yet in spite of its high price xanthogenate of potassium is 

 used in disinfection and enters into the composition of certain insecti- 

 cides. 



Phylloxera vastatrix, Planch, (phylloxera of the vine). — Dr. 

 Koenig, director of the Agronomical Station of Nice, has made very 

 extended trials of the action of this salt on phylloxera, and found that 

 compared with carbon disulphide and sulphocarbonate of potash its 

 value as a disinfectant of phylloxera-infected vines was greater and 

 more certain. The eggs and phylloxeras are killed without exception 

 by submitting them to the action of solutions of xanthogenate of potas- 

 sium or to that of the vapours which its solution emit on heating. 

 To disinfect the roots Koenig recommends the use of aqueous solu- 

 tions. The disinfection of ornamental plants suspected of phylloxera 

 and intended for export is carried out at the Nice station by Koenig's 

 process alone. 



Scliizoneura lanigera, Hausm. (woolly aphis). — Muhlberg recom- 

 mends to combat the woolly aphis an insecticide known as knadolin, 

 which whilst preserving the properties of Nessler's contains two most 

 active substances, nitrobenzene and xanthogenate of potassium. Amyl 

 alcohol 60 lb., soft soap 40 lb., nitrobenzene 2 lb., xanthogenate 1 lb., 

 water 6 gallons. Knadolin in 2 per cent solution kills the greater 

 number of insects injurious to plants. To «.pply it the wounds and 

 cankers caused by the American woolly aphis are coated with a solu- 

 tion of 1 part of this insecticide in lo parts of water. 



37. Potassium Cyanide, KCN. — Preparation. — Potassium 

 cyanide is formed each time that carbon and nitrogen come in contact 

 at a high temperature with an alkali or an alkaline carbonate. Com- 

 mercially potassium cyanide is prepared by submitting nitrogen or 

 organic bodies rich in nitrogen to the action of carbon impregnated 

 with potash and heated to redness. Prussic acid or hydrocyanic acid 

 is generated by the action of an acid on potassium cyanide. The 

 latter, however, does not cede all the hydrocyanic acid which it con- 

 .tains. 



Properties. — Potassium cyanide crystallizes in deliquescent cubes ; 

 it is found in commerce as fused white plates which must be kept out 



