POTASSIUM CYANIDE (PEUSSIC ACID). 131 



of contact with air because that decomposes it rapidly into hydrocyanic 

 acid and carbonate of potash — 



2KGN + H.O + CO. = K.COg + 2HCN. 



The commercial product is never pure, it always contains a greater 

 or less amount of carbonate of potash. Prussia acid is a colourless, 

 very volatile liquid having the odour of bitter almonds. It is, like its 

 salts, a dreadful poison. The vapours given off by decomposition in 

 contact with air kill the insects and animals which breathe it in a few 

 minutes. Its action is the same in whichever way it be intro- 

 duced into the body, by digestion, respiration, or introduced into the 

 blood through a wound. A drop of hydrocyanic acid placed on the 

 eye of a dog causes it to -die in a few seconds a dreadful death. The 

 respiration of the vapours of this acid induce giddiness, then death. 

 The mortal dose for a man is 0-06 gramme, say 1 grain, of prussic 

 acid and 0*15 gramme, say 2^ grains, of potassium cyanide. According 

 to Preyer, prussic acid acts through the compounds which it forms 

 with the haemoglobin and the oxyhaemoglobin of the blood. 



Action on Plants. — All cyanogen compounds have a poisonous 

 action on plants, but it is prussic acid which possesses this property 

 in the highest degree. As far back as 1827, Goppert remarked that 

 prussic acid prevented the germination of grain, and absorbed by the 

 plant it killed it in one to three days. When a plant is watered with a 

 dilute solution of cyanide the latter is absorbed and distributed through- 

 out all parts of the plant by the sap ; the leaves turn yellow, then brown, 

 and the turgescence of the cells of the parenchyma is abolished. 

 Perosino succeeded in injecting a very dilute solution of potassium 

 cvanide into the trunk of a tree without hurting it, and after two days 

 all trace of this product had disappeared in the sap, but the dose to be 

 withstood was, it is true, infinitesimal. Berlese has shown that trees 

 withstand these injections badly, even in small doses. Mouillefert made 

 a very complete examination of the action of potassium cyanide on 

 vines and adventitious plants. 



Exijeriments made in July on Healthy Vines, variety Saint Emilion. 

 — Placed in pots, each containing 3 litres of soil, three vine stocks 

 were watered with (1) 170 milligrammes of cyanide, say a 0-142 per 

 cent solution ; (2) 250 milligrammes of cyanide in 140 cubic centi- 

 metres of water, say a 0-18 per cent solution ; (3) 500 milligrammes of 

 cyanide dissolved in 180 cubic centimetres of water, say a 0-28 per 

 cent solution. In six days vine No. 3 was dead, that carrying No. 2 

 was greatly inconvenienced, and No. 1 seemed to suffer. As will be 

 seen from these results the substance is highly poisonous to the vine, as 

 a dose of 0-008 per cent of potassium cyanide in the soil kills this plant. 

 Guerrieri estimates that a dose of 1 gramme suffices to kill an adult 

 vine, and that it is impossible to kill the phylloxera by this method, the 

 vine being as sensitive as the parasite. The fact that the phj-lloxeras 

 of a vine treated with cyanide die mainly by the absorption of the 

 poisoned juice, shows that this method of treatment must be as per- 

 nicious to the vine as to the phylloxera ; Chittenden considers that it 

 is impossible to treat all plants by hydrocyanic acid vapours to free 



