88 INSECTICIDES, FUNGICIDES, AND WEED KILLERS. 



not be exceeded, for there would be the risk of too small a crop which 

 would be as great an evil. 



Use of Sulphuric Acid against Insects and Worms. — 



Tylenclms Tritica [Bastian] (eel-worm of wheat). — This is a microscopic 

 worm which causes the blight known in France as Nielle de Froment 

 [and in Great Britain as "Ear Cockles," "Purples," "False Ergot," 

 " Galls of Wheat Eel- worms "]. Davaine in 1889 recommended steep- 

 ing the affected grain in 0-5 per cent sulphuric acid for twenty-four 

 hours, but this method has the drawback of injuring the grain. 



Tortrix Vitana (pyralis of the vine). — The winter treatment 

 against anthracnose of the vine by sulphuric acid, not only destroys 

 the spores of the most formidable cryptogamic parasites, but according 

 to Debray it also destroys the grubs of this butterfly which pass the 

 winter in the interstices of the bark. According to the same observer 

 the vine cochineal Dactylopius Vitis, which passes the winter fixed 

 against the wood, may be desti'oyed by spraying with 10 per cent 

 acid after the fall of the leaf. The acid employed under like con- 

 ditions to destroy the Schizoneura lanigera, Haus, did not give the 

 result expected. To kill ivasjjs it suffices to pour 10-20 per cent acid 

 into the nest. 



8. Chlorine, CI.,. — Chlorine is an element widely distributed in 

 nature in combination with certain metals — sodium, potassium, 

 magnesium. 



Preparation. — -By the action of aqueous hydrochloric acid on 

 manganese dioxide. 



MnO^ + 4HC1 = MnCl, + 2H,0 + CI, 



Mangan- Hydro- Mangan- Water. Chlorine, 



ese chloric cue 



dioxide. acid. chloride. 



Use.— This gas, of some use to kill fungi, is so poisonous to plants 

 that its use is limited to saprophytic fungi, such as^ 



Meruliiis lacryinans, Schm. (dry rot of wood). — As a remedy 

 chlorine is the subject of a German patent, D.E.P. 76877, accoi^ding 

 to which good results are obtained by piercing boards with holes into 

 w^hich chlorine is introduced ; these holes are then stopped up hermeti- 

 cally. 



Q. Hydrochloric Acid, HCl. — Preparation. — The industrial pre- 

 paration of this acid is subsidiary to the manufacture of sulphate 

 of soda, intended for the production of soda ash. It is produced by 

 decomposing common salt by sulphuric acid. 



2NaCl + H._,SO, = Na,,SO, -f 2HC1 

 Sodium Sulphuric Sodium Hydro- 



chloride, acid. sulphate. chloric 



acid. 



The salt is introduced into capacious cast-iron cylinders, luted with 

 clay, and then sulphuric acid is run on to it. The hydrochloric acid 

 which escapes is dissolved in earthen carboys containing water. Com- 

 mercial HCl marks 22° by Baume's hydrometer. 



Use. — The searching examinations which have been made into the 

 action of this acid on fungi have shown that its use is not advisable. 



