CALCIUM SULPHIDE. 149 



proportions. Moistened with water and in contact with air they are 

 rapidly converted into carbonate of lime and sulphuretted hydrogen. 



CaS, + CO, + H,0 = CaCO^ + H.S + S. 



But simultaneously with this decomposition they undergo partial 

 oxidation into hyposulphite of lime. Calcium sulphides are neutral. 

 They act by the amount of sulphvir which they contain. To prevent their 

 too rapid decomposition in moist air, various substances have been incor- 

 porated, such as glycerine and milk of lime, in the proportions given 

 by Mohr (p. 148), molasses, soft soap, in the proportion of 1-2 per cent. 

 These substances also cause the bouillies to adhere better to plants. 



Action on Plants. — -Calcium sulphides are less injurious to the 

 green parts of plants than potassium sulphides, because their solutions 

 are not caustic. Solutions of glycerinated monosulphide may dry on 

 the leaves without injuring them. But in spite of that it is necessary 

 to avoid the too rapid decomposition of these sulphides for the 

 sulphuretted hydrogen produced is very injurious to the plant ; 0'75 

 per cent of this gas diffused through the air may poison certain plants. 

 The use of glycerine to form bouillies, and of water and lime to dilute 

 them prior to use, helps greatly to attenuate the effect of this gas ; by 

 delaying the decomposition of the sulphides, too large an amount of 

 sulphuretted hydrogen is prevented from being formed at one time. 

 The damage caused by different plants, as well as on the roots 

 treated, are likewise caused by hyposulphite of hme often present in 

 impure calcium sulphides ; hyposulphites scorch the leaves especially 

 during strong summer heat. Owing to their reducing action sulphides, 

 and particularly calcium sulphides, are injurious to the roots which 

 come in direct contact with it. The experiments of Fithbogen, 

 Schiller, and Forster have proved this effect. 



Action on Fungi. — The action of calcium sulphide on the 

 mycelium of fungi is in principle the same as that of sulphur, but 

 poly sulphides, which are in a way solutions of sulphur, may be looked 

 upon as more active than sulphur, even used in its most impalpable 

 form. Whilst sulphur has no radical action on the Eri/siphecE, the 

 mycelium of which is exposed without any protection on the surface 

 of plants, calcium sulphides act on fungi which live in the plant itself. 



Action on Insects. — Generally insects are not disturbed by solu- 

 tions of calcium sulphide. It is otherwise with acari, plant lice, which 

 are easily destroyed by this preparation. Sulphides are, so to speak, 

 specifics against the PhytojHides which produce the different erinoses 

 of plants and the most diverse galls. Used against these lice their 

 action, otherwise very imperfect, is solely due to the sulphuretted 

 hydrogen given off, which is exceedingly poisonous to these insects. 



Use against Fungi. — Calcium sulphides form an efficacious and 

 economic means for the destruction of the most various parasites. They 

 are practical substitutes for sulphur. They have in themselves a re- 

 markable action ; but it is well to incorporate in their solutions sub- 

 stances capable of protecting them against moist air which renders 

 them inactive too soon and causes them to poison plants. Mohr 

 advises their use against cryptogamic diseases. 



