858 INSECTICIDES, FUNGICIDES, AND WEED KILLERS. 



Psylla Mali, Forst. (chermes of the apple-tree). — It is overcome 

 by a solution of carbolic acid O'O per cent and soft soap 0-5 per 

 cent. 



EriopJiye'< ribis (phytoptus ribis, currant gall mite). — It may 

 be overcome by a mixture of carbolic acid 3 gallons, s':ft soap 30 

 lb., in 500 gallons of water. Fiist spraying in spring, second in 

 autumn. 



/NO, 



^33- Trinitrophenol or Picric Acid, C„H,(^ <^ ^^- . Prepara= 



\0H 

 tion. — -Picric acid is the most important of the nitrated deriv- 

 atives of phenol (carbolic acid). It is obtained by heating carbolic 

 acid with an excess of fuming nitric acid or by pouring nitric acid drop 

 by drop into carbolic acid dissolved in sulphuric acid. Crude picric 

 acid, which separates from the liquid after cooling, forms crystals 

 which are collected. After draining they are dissolved in caustic soda ; 

 the picrate so formed is crystallized and decomposed by sulphuric acid. 



Properties. — Picric acid crystallizes in yellow plates of a bitter 

 taste soluble in 86 parts of water at 15° C. and in 26 parts of water 

 at 77° C. It dissolves better in alcohol. Its salts are explosive. 

 Picric acid is used in medicine against intermittent fever (Dujardin- 

 Beaumetz and Clark). It has been recommended against trichinosis 

 and the solitary worm. It is of current use in treating burns. Picric 

 acid precipitates albumen in the same way as powerful insecticides ; it 

 is highly antiseptic.^ 



Action on Plants. — Experiments on this point are few; however, 

 trials on the vine show that the vine supports with impunity coatings 

 and washings of its roots. With a dose of 40 grammes per stock (616 

 grains) there is as yet no poisoning. 



Use. — Picric acid has been tried in Germany as " Eeflorit," com- 

 paratively with blue vitriol, but w thout success, for the disinfection of 

 seed-corn against TiUetia and Ustilago (Sigmund, 1896 ; Burmester, 

 1908). The corn was too sensitive to its action. The results obtained 

 by its use against mildew, oidium, cochylis, and chlorosis were negative 

 (Colmar Experimental Station, 1908). 



Action on Insects. — The action of picric acid much resembles 

 that of " Antinnonine ". The first experiments on phylloxera were 

 made by Eommier. He found that by watering a vine in pot with 

 150 cubic centimetres of water containing 2 grammes of picric acid, 

 all the phylloxera were killed in a few days. Experiments on the 

 large scale did not give such a satisfactory result. Although each 

 stock received 40 grammes of picric acid in solution, although this 

 operation was followed by rains favouring the diffusion of the insecticide, 

 and although the earth was soaked with it to such an extent that it 

 tasted bitter, the phylloxera of the lower layers were still living eighteen 

 days after treatment. 



^ Trannlator's Note. — All nitro derivatives and their metallic salts, moieesi)eci- 

 ally picric acid and picrates, are highly exp'osive, and tlaeir storage is attended with 

 extremely great danger. A special licence is required. 



