POTASSIUM CYANIDE (PBUSSIC ACID). 135 



cyanide ; the phylloxeras and their eggs were all dead when it was 

 lifted out. 



Experiinenis on Phylloxera : Fumigation. — Five milligrammes of 

 potassium cyanide, yielding by decomposition 1*7 cubic centimetres of 

 prussic acid vapour, were placed in a flask of 2100 cubic centimetres, 

 then a phylloxera-infected root. When the action was complete the 

 atmosphere of the flask consisted of 8 parts of prussic acid vapour 

 per 10,000 parts of air. After fifteen hours there were no living 

 insects. It follows that potassium cyanide is about ten times more 

 poisonous than potassium sulphocarbonate, for it suffices for an 

 atmosphere to contain 0'08 per cent prussic acid gas to obtain the 

 same result as with 0"75 of a mixture of equal parts of sulphuretted 

 hydrogen and carbon disulphide, disengaged from potassium sulpho- 

 carbonate. Under a cloche 0-000240 of potassium cyanide kills plant 

 lice. 



Experiments on Phylloxera : Action by Poi&oning. — A phylloxera- 

 infested root was immersed by its extremities in a 0-125 per cent 

 solution of potassium cyanide with the precautions necessary to hinder 

 the phylloxera being exposed to prussic acid vapours. After ten 

 minutes' treatment the adult phylloxera, the nests of which were sunk 

 in the tissues of the root, were dead, the greater number of the larvae were 

 alive. The cyanide can thus poison the sap, and in that way reach 

 the phylloxeras fixed on the roots. Mouillefert having shown that 

 potassium cyanide acted in a very poisonous manner on the phylloxera, 

 and that an infinite quantity killed these insects either by contact or 

 by poisoning the sap, the substance may be regarded as of great 

 service in agriculture. 



1. Experiments on Phylloxera-infected Vines, in pots containing 

 3 litres of earth, on 10 July. A dose of 150 milligrammes of KCy 

 in 400 cubic centimetres of water (a 0"0375 per cent solution) gave a 

 complete result without injuring the vine, whilst a dose of 500 milli- 

 grammes in 500 cubic centimetres water caused it to suffer greatly. 

 A dose of 1 gramme in .the same amount of water killed it. 



2. Experiments on Vines in Vineyards, made on 6 July. The 

 stocks were stripped to a depth of about 15 centimetres, with a radius 

 of 30-35 centimetres (12-14 inches), the soil being rather dry. After 

 pouring on the potassium cyanide solution the soil was replaced at the 

 foot of the stocks and strongly packed. The dose used varied from 

 20-50 grammes (307-767 grains) per stock, dissolved in 10 litres (2-2 

 gallons) of water. Wherever the solution had penetrated, the phylloxera 

 and their eggs were dead. But at a depth of 40-45 centimetres (16- 

 18 inches), as well as between the stocks in a radial direction, even by 

 using five times more water the result was incomplete. Trials with 

 the pal-hole method gave no better results, and Mouillefert concluded 

 that potassium cyanide was incapable of producing a complete result 

 in agriculture on the large scale, because its action is only felt where 

 the solution can penetrate. The prussic acid disengaged in the soil 

 cannot diffuse through its layers like carbon disulphide, neither does 

 F. Guerreri believe it possible to use this substance against the phyl- 

 loxera, for he found that the plant did not resist the doses required 



