Insecticides and Related Substances. 307 



an earthen- ware vessel. Potassium sulphate is formed and the 

 poisonous hydrocyanic acid is rapidly liberated as an invisible 

 gas. This is an extremely powerful poison, a single breath being 

 fatal, and by no means should it be inhaled by the operator. 

 To retain the gas and secure efficient action, it should be applied 

 in tightly closed rooms or buildings, or in tents specifically pro- 

 vided for the purpose, allowing it to act for an hour or more. 

 The enclosure should then be opened from the outside and thor- 

 oughly aired before being entered, and the strongly acid residue 

 from the reaction should be carefully disposed of. 



Carbon bisulphide is a colorless, volatile liquid formed by pass- 

 ing sulphur vapors over red hot charcoal. The gas evolved from 

 the liquid is heavier than air, inflammable and fatal to insects 

 breathing it. Its chief use is for the destruction of weevils in 

 grain. One teaspoonful for each cubic foot of space should be 

 placed in a shallow dish at the surface of the grain, and one hour 

 allowed for the evaporation of each teaspoonful used. The heavy 

 vapors sink through the grain to the bottom of the bin, where 

 they may be released by boring holes through the wall. Ants, 

 moles, prairie dogs and similar pests are exterminated by placing 

 cotton saturated with carbon bisulphide in the heaps or runs and 

 covering tightly. Carbon bisulphide should never be brought 

 near flames. 



Fungicides are materials utilized for the destruction of para- 

 sitic plants. Hyposulphite of soda, lime-sulphur and sulphur 

 alone were used in this capacity as early as 1885 against apple 

 scab and leaf blight. 



Bordeaux mixture has been the premier fungicide since 1883, 

 when Millardet used it against the downy mildew of the grape. 

 It was accidentally discovered by observing the flourishing con- 

 dition of vines to which lime and copper salts had been applied 

 to prevent the theft of grapes in the province of Bordeaux, 

 France. Several formulae have been superseded generally by 



