POTASSIUM SULPHOCAEBOKATE. 123 



and the chitia so as to let the toxic substances reach the parasite and 

 act on it more rapidly. 



Wood ashes are also utilized to kill slugs, using preferably that from 

 lime-kilns, as it still contains lime, the action of which aids the carbon- 

 ate of potash. After a rain in the evening the ashes are spread broad- 

 cast on the seed beds of whatever nature ; it exerts no injurious action 

 on the plant but kills snails instantly on touch. It is well to water 

 the plants next morning and recommence the treatment after sunset. 

 In vineyards where slugs are dreaded vines are heavily dusted with 

 ashes. 



35. Potassium Sulphocarbonate, K,CS3H.O. — Preparation. — 

 By agitating potassium monosulphide K^S, with an excess of carbon 

 disulphide. If a pure product be not desired liver of sulphur may also 

 be used. 



Properties. — Carbon disulphide acts as an acid towards alkaline 

 sulphides and forms compounds therewith analogous in constitution to 

 the alkaline carbonates K„SCS^. 



But these compounds are unstable ; the moisture and carbonic 

 acid in the air decompose them thus — 



K._,CS3 + CO., + H,0 = K.COg + CS., + HoS 



into alkaline carbonate, carbon disulphide, and sulphuretted hydrogen. 

 Organic acids act in the same way. This decomposition goes on 

 slowly in the air and in the soil, according to the moisture of the sur- 

 rounding media and the richness in carbonic acid. The dry crystals 

 contain 38 per cent of carbon disulphide and can disengage 17 per cent 

 of sulphuretted hydrogen ; 100 grammes of 40° B. commercial solution, 

 which tests 55 per cent of pure potassium sulphocarbonate, can give 

 off on decomposition 20 per cent of carbon disulphide, say 6 litres, and 

 9 per cent of hydrogen sulphide, say 6 litres. Potassium sulpho- 

 carbonate is in the solid condition a yellow crystalline very deliquescent 

 body. But it is very difficult to obtain in that form, and the commercial 

 article is liquid and marks 35°-40° B. It is soluble in water in all 

 proportions. [Alkaline sulphocarbonates treated by hydrochloric acid, 

 then taken up immediately by water, yield a reddish-brown insoluble 

 liquid which represents sulphocarbonic acid ; it is used in therapeutics. 

 It readily decomposes into CS., and H,S. The sulphocarbonates which 

 chemically contain carbon disulphide have no analogy with the sulphide 

 mixed with tar, vaseline, oil, or soap, the use of which has been pro- 

 posed to replace the pure sulphide.] 



Action on Plants. — Sulphocarbonate when concentrated is a 

 violent plant poison. The two gases [CS^, and H,Sj which it liberates 

 are likewise poisons, but their action is less energetic than that of the 

 sulphocarbonate itself. Trials on healthy vines in 3-litre pots at 

 different seasons of the year show that the vine is more sensitive in 

 summer during the activity of the sap than in winter. Thus in 

 August, vines do not stand a dose of 12 cubic centimetres of 10° B. with 

 or without water, whilst a dose of 15 cubic centimetres may be given 

 in winter, and even in April when already the vine has big buds. Now 

 15 cubic centimetres of sulphocarbonate of 40° B. can only disengage 3 



