82 INSECTICIDES, FUNGICIDES, AND WEED KILLERS. 



Sitotraga ccreallela (grain mite). — So that the S0._, may penetrate 

 well into the heap of wheat and kill all the grubs, Bernard Saint 

 Ubery burns the sulphur in chafing dishes around which the grain is 

 piled in heaps. To destroy butterflies the process used against the 

 Colander gives good results. It suffices to place 1 inch to 1-^ mch of 

 sulphured wick on slates laid on the heap of wheat, and to set fire to 

 the wick. By analogy it was thought possible to destroy by the same 

 gas the grubs which live in flour. 



Asopia farinalis (flour mite). — The process recommended by 

 Debray consists in burning in closed vessels 60 grammes of sulphur 

 per cubic metre of flour ; the method was regarded as obnoxious, the 

 flour being rendered unfit for bread-making ; Balland found this flour, 

 whilst presenting no visible alteration, is appreciably altered in contact 

 with sulphurous acid. The gluten has lost the valuable properties re- 

 quired in baking. It is recognized, in fact, that gluten gains in value 

 by contact with alum, common salt, or blue vitriol, but that it cannot 

 stand the action of sulphurous acid, SO.,, nor sulphuric acid, SOg, 

 nor sulphuretted hydrogen, SH^. To destroy the tinea of grain, SOg 

 must not be used, but insecticides like CSo. 



Tortrix or Pyralis vitana (pyralis of the vine). — The grubs hiber- 

 nating in the fissures of the bark of the vines can be killed by SO^. 

 The process employed in the South of France is known by the name 

 of dockage, or sulphuring of the vine. After pruning the vine, each 

 stock is covered by a zinc cloche, or half a petroleum barrel, under which 

 20-25 grammes of sulphur (say f oz.) are burnt in a saucer. The 

 SO2 formed soon saturates the air under the cloche, and stifles the 

 grubs sheltered in the interstices of the bark. The operation should 

 not last longer than five to ten minutes, a more prolonged action having 

 a deadly effect on the vine. A workman provided with twenty cloches 

 can sulphur 1000 stocks per day. The cost is 48 francs per hectare 

 if brimstone be used and 75 francs if wicks be used, say 15 and 24 

 shillings per acre. It is thus cheaper to use brimstone. It is a very 

 delicate operation, which may well be replaced by scalding, but its use 

 is still widespread. So that it may succeed, it must not be done 

 when the soil is moist, for the SO.,, instead of saturating the air, would 

 be absorbed by the humidity in the soil. Clochage kills at the same 

 time as the pyralis the vine cochineal and the red spider. Eeh found 

 that all coccides shielded Homoptera, such as Diaspis, Aspidiotes, 

 Lecanium, Ceroplastes, and cochineals, which resist all insecticide spray- 

 ing, may be destroyed by SO.^ fumes. The fruit trees are covered 

 with a tent, and sulphur burnt therein, observing the same precautions 

 as in the clochage of the vine. 



7. Sulphuric Acid, H^,SO^. — Sulphuric acid is obtained by passing 

 a mixture of oxygen and sulphurous acid over spongy platinum or pla- 

 tinized asbestos, heated to between 250° C. and 500° C. (482"-932° R). 

 The vapours of SO3 disengaged are led into a receiver surrounded by 

 a freezing mixture, where they condense. The process of manufacture 

 usually adopted is to oxidize sulphurous acid by nitric acid vapours and 

 to hydrate the vapours in lead chambers. The necessary SO3 is 

 obtained by "burning" iron pyrites in presence of an excess of air. 



