ARSENIOUS ACID. 95 



Gillette found that in a much weaker dose arsenic is still injurious, 

 and that, in this respect, different plants are not equally sensitive. 



These doses being often insufificient to kill the insects, arsenic 

 solutions were completely abandoned, and replaced by neutral bouillies, 

 in which the arsenic is generally in the insoluble condition, and thus 

 in a form which does not injure the plant. Arsenious acid has also 

 a very decided action on the spores of fungi. This action was long 

 known and utilized to disinfect cereal grains, when, in 1856, Boussin- 

 gault recommended the use of arsenite of soda for the disinfection of 

 grain. This process was, in his opinion, the best for freeing farm crops 

 from smut, bunt, rust, caries and ergot ; it, moreover, had the advan- 

 tage of protecting the grain from the ravages of injurious animals 

 after sowing. 



Use. — The French Ordinance of 1846, Article 10, " The sale and use 

 ot arsenic and its compounds are interdicted for the pickling of grain, the 

 embalming of corpses, and the destruction of insects," has prevented 

 its use in France, but in other countries the valuable properties of this 

 product have earned for it numerous applications. The first trials 

 were made in America in 1867, when Markham used arsenic to com- 

 bat an insect very deadly to the potato, the Leptinotarsa decemlineata or 

 Doryphor of Colorado (the Color-ado beetle). The use of arsenic 

 became general in 1871, but especially in the form of neutral bouillies, 

 with an emerald green or Scheel's green basis, London purple or 

 arsenite of lime, or in admixture with different anti-cryptogamic salts. 

 Gillette also recommended, in the form of powder, mixed with much 

 flour. In this form it has 'been recognized as less injurious to the 

 leaves than in solution, and is thus recommended every time that spray- 

 ing cannot be adopted. To-day white arsenic is hardly used except to 

 poison the pastes for the following insects : Agriotes Imeatus or Elater 

 segetis, L. (wire worm), injurious to cereals ; Agriotes or Elater 

 sputator, L. (spitting click beetle), injurious to lettuce ; Agriotes or 

 Elater obscurus, L. (dusky click beetle), injurious to carrots. It is 

 very difficult to get at the larvae, as they live hidden. Comstock re- 

 commends to destroy them by pastes poisoned by arsenic. For this 

 purpose small bundles of lucerne are prepared towards July, of which 

 the larvae are very fond ; they are dipped in a 1 per cent solution of 

 arsenious acid, they are then placed in the infected fields, taking care 

 to cover them with flower-pots so as to keep the lucerne moist which 

 should always appear as if fresh cut. 



Gryllotaljja vulgaris (mole- cricket). — To poison this insect Leh- 

 mann spreads in the spots frequented by it preparations made thus : 

 thyme, sweet marjoram, sweet basil, with ground arsenic, earth, or 

 sand. The mole-crickets, very fond of these seeds, come to eat them 

 and are poisoned. 



Acrydium migrator mm (Gviquet migrateur) ; Acrydium p)eregrinum 

 (Criquet pelerin). — Chemicals are only rarely used to combat these 

 locusts ; battues and Cypriot's apparatus are preferred. However, 

 Coquillot recommends the use of poisonous preparations. One lb. of 

 sugar is dissolved in enough water to form a syrup, there is then 

 stirred in 1 lb. of arsenic and 6 lb. of bran. This paste is divided into 



