POTASSIUM SULPHIDE (LIVER OF SULPHUR). 113 



Liver of Sulphur is a mixture of polysulphides, but it contains 

 especially the pentasulphide of potassium. It is preferably obtained 

 by heating to redness in a crucible equal parts of sulphur and car- 

 bonate of potash. By the action of heat the carbonic acid is disen- 

 gaged and the sulphur combines with the potassium. When the 

 disengagement of carbonic acid is finished, the liquid is run on to an 

 iron plate where it solidifies immediately ; it is then broken up and 

 preserved out of contact with air. It forms a reddish- brown solid 

 which smells of rotten eggs. 



Properties. — The sulphides are very deliquescent and soluble in 

 water in all proportions. They must be kept out of contact with air ; 

 carbonic acid in presence of moisture rapidly decomposes them into 

 potassium carbonate and hydrogen sulphide. Solutions of the mono- 

 sulphide are colourless, those of polysulphides, on the other hand, are 

 yellow. Sulphides retain the alkaline properties of caustic potash, 

 attenuated by sulphur. In medicine, sulphides 'are used to treat skin 

 diseases due to acarium. Plants do not stand spraying with sul- 

 phide solutions, these being generally used very dilute. The sul- 

 phuretted hydrogen given off by decomposition is poisonous to the 

 plant in a 0-75 per cent dose, but it is only formed gradually, so that 

 the amount in contact with the plant is not sufficient to cause any 

 ill effect. Leaf burning is less frequent than with sublimed sulphur. 



Use. — Sulphides are used to combat : (1) Ch-yptogamic diseases, 

 either by spraying the plants or by immersion to disinfect the seed 

 against anthracogenic parasites. (2) To kill insects. To impart more 

 adherence and a longer action, a soap and glycerine emulsion is used. 

 Polysulphides of potassium are used in the same proportion as sulphur, 

 for they decompose under the action of cavbonic acid and air and or- 

 ganic acids into potash salts, hydrogen sulphide, and sulphur : — 



K^Sg + CO., -1- K,0 = K.,C03 + H,S + 4S. 



The sulphur is pi'ecipitated in a fine state of division, and thus its 

 anticryptogamic properties are at a maximum. It can thus be said 

 that the action of polysulphides is appreciably identical with that of 

 sulphur, and especially of precipitated, impalpable sulphur if used in 

 the same temperature conditions. In studying their application it 

 will be seen that they have entered into current practice as substitutes 

 for sulphur in killing numerous Erysiphece and to stop the develop- 

 ment and extension of certain fungi by the destruction of their coni- 

 diophores. In sulphides the caustic action aids that of sulphur. Not 

 only do sulphides have a decided action on fungi and their spores, 

 but the potassium carbonate formed by their decomposition has a de- 

 cided action on fungi, whose growth it prevents. The growth pi conidia 

 of phytoplithora and of peronosjjora is stopped by a 0'7 per cent solu- 

 tion, their zoospores being no longer able to develop. The spores of 

 Ustilago Carbo and of Claviceps 'purpurea as well as the uredospores 

 of Puccinea are more resistant than the former, for a 0'7 per cent solu- 

 tion hardly hinders their growth, whilst a 3-5-7-5 per cent solution 

 stops it. 



As insecticides, sulphides act in virtue of their caustic properties, 



