INORGANIC POISONS 247 



cheapest of the sulphide class. It is made by boiling 50 Ibs. 

 of lime, 100 Ibs. of sulphur and 100 galls, of water 

 for about three hours. The resulting liquid is allowed 

 to settle, which it does very quickly, and the clear orange- 

 coloured liquid is syphoned off into well-corked bottles. The 

 liquid has a gravity of ri6 and contains 97-9*8 % sulphur 

 precipitable by mineral acids and 2'8 % lime alkaline to 

 methyl orange. Some brands on the market are double 

 the above strength. The stock solution is diluted ten or 

 twenty times for spraying. 



The quantities of material used and found in the product 

 show that the reaction during manufacture is : 



3CaO + 128 = 2CaS 5 + CaS 2 O 3 



On adding hydrochloric acid all the sulphur is precipitated 

 and after boiling may be filtered off on a Gooch crucible 

 and weighed. On titrating with methyl orange only the 

 CaS 6 reacts. On passing carbon dioxide into the spray 

 liquid the CaS 2 O 3 is not decomposed but the CaS 6 gives 

 CaC0 3 4-H 2 S+S 4 . 



Liver of Sulphur, Potassium Sulphide. This well- 

 known insecticide is made by heating potassium carbonate 

 and sulphur and pouring the fused mass on to a cold surface. 

 The material easily dissolves in water to make a solution 

 of about | %. To this is usually added an equal amount 

 of caustic soda, sodium carbonate or soap. Strong solutions 

 can be prepared, but must be well corked and bottled until 

 they are needed for dilution. 



The potassium in the above can be replaced by sodium 

 without any decrease in power. The advantage of using 

 sodium or potassium in preference to calcium only occurs 

 when it is desirable to add some alkali or soap to the poly- 

 sulphide. The admixture of alkali or soap is particularly 

 useful for destroying the waterproofing of the wax coated 

 cuticle of the insect (see pp. 246, 251). L,ime sulphur wash has 

 little power in this respect and hence insects shed the fluid 

 off their backs like the proverbial duck. Strong solutions 

 of liver of sulphur can also be made by boiling 70 Ibs. of 



