90 INSECTICIDES, FUNGICIDES, AND WKKD KILLERS. 



lo. Nitric Acid. — Preparation. — The commercial acid is prepared 

 by introducing into a cast-iron pan 330 kilogrammes (726 lb.) of nitrate 

 of soda and 420 kilogrammes (964 lb.) of sulphuric acid of 62^ 

 Baumo ; the lid is luted with clay and heated. The nitric acid vapours 

 disengage through an earthen pipe, condense in big carboys, also of 

 eai-thenware, placed one after the other, and each containing a little 

 water. There are thus obtained 440 kilogrammes (968 lb.) of nitric 

 acid of 36° Baume. 



Properties. — Nitric acid is a colourless liquid, sometimes yellow 

 from the presence of nitrous acid. Its density is 1'02, its boiling- 

 point is 86" C. It is very corrosive; in contact with organic matters 

 it first produces nitrated compounds, then an oxidation which proceeds 

 so far as destruction. It is quite as dangerous as sulphuric acid, and 

 should be handled with many precautions. 



Action of Nitric Acid on Plants. — The following are the results 

 of the examination of nitric acids on plants : 0"05 gramme of this 

 acid in a cubic metre of air produces poisonous effects on plants 

 analogous to those produced by sulphurous acid ; spots and brown 

 borders on the leaves ; yellow points on the needles of the conifers. 

 The normal dose of nitric acid in the air is '00003 per cubic 

 metre ; it therefore requires a dose almost 2000 times stronger to pro- 

 duce pathological symptoms in the plant such as occur in the neigh- 

 bourhood of factories which allow the vapour of these acids to escape. 



Use. — Nitric acid is not only corrosive but poisonous to insects. 

 This latter property is manifested, more especially, in organic com- 

 pounds containing one or more nitro groups. Nitric acid, like sulphuric 

 acid, has been recommended especially to combat insects in winter. 

 Its action on fungi is especially injurious. Hitchcock and Carleton 

 found that the uredospores of Puccinia coronata, Corda (crown rust of 

 oats) are killed in twenty-four to twenty-six hours in nitric acid of 0"68 

 per cent, but an acid of 0*068 per cent has no action on these spores. 



The spores olPhytophthora and Peronospora, according to present 

 knowledge, are destroyed by an acid of about 0"05 per cent. Nitric 

 acid is not used to combat fungoid parasites except black rot, although 

 it has been tried against several other cryptogams. 



Guignardia Bichvells, Viala et Ravaz (black rot). — Viala, the learned 

 professor of Grignon, proposes to replace sulphuric acid in the winter 

 treatment of the vine by_ nitric acid, which destroys the spores of this 

 fungus. Against insects the first experiment dates as far back as 1872. 

 Lemoine recommended for the treatment of the phylloxera the coating 

 of the stems with a mixture consisting of 1 kilogramme of nitric acid 

 of 60 per cent, 2 grammes of spirits of turpentine, and 4 grammes of 

 chrome yellow, the whole diluted in 5 litres of water. Examined by 

 the commission who investigated the chemical products proposed to 

 combat this insect the above mixture was pronounced defective. 



At the present time it is recognized that nitric acid is very injurious 

 to grubs and may be used wherever these are not on the vegetative part 

 of the plant. By this method the grubs of the Tortrix Vitana (pyralis 

 of the vine) and the Conchylis Ambignella, Hubn (cochylis of the 

 vine), which pass the winter in the fissures of the bark of the stem. 



