198 iNSECTifn)];s, fungicides, and weed killers. 



Properties. — Silver nitrate is soluble in half its weight of water 

 and in the tenth of its weight of boiling water ; it dissolves also in 10 

 parts of cold alcohol and 4 parts of boiling alcohol. Fused and run 

 into sticks silver nitrate yields the infernal stone used in medicine. 

 Silver nitrate decomposes readily ; it is slowly reduced by light and 

 organic matter to silver oxide. In medicine it is used to cauterize 

 wounds and remove false membranes (proud fiesh) ; internally it is 

 used in doses of 1-4 centigrammes ; in greater doses it is poisonous. 

 It is an antiphlogistic and sedative. Silver nitrate combines with 

 albumen, forthwith forming a precipitate of an albumen salt soluble 

 in excess of albumen and in solutions of common salt. Nitrate of silver, 

 therefore, behaves towards albumen like many powerful antiseptics. 

 Its powerful action on spores and microbes results from these pro- 

 perties and its action on the living plasma. In very dilute solution 

 it interferes with the vitality of the plasma which on contact therewith 

 blackens owing to the metallic silver formed. 



Action on Plants. — It suffices to water plants with a very dilute 

 solution of nitrate of silver to kill them infallibly. To prevent wheat 

 from germinating it suffices to steep it in a bath containing 0-029 

 gramme of nitrate of silver per litre, that is, 29 lb. in 10,000 gallons. 



Action on Fungi. — Nitrate of silver is as injurious to fungi as to 

 plants. It only requires an infinitesimal dose of this substance, which 

 analysis cannot detect, to prevent the spores of the saprophytic fungus, 

 Aspergillus niger, from germinating (Eaulin). 



Use. — Silver nitrate is not used as an anticryptogamic in the 

 struggle against the diseases of plants, its action on the latter being 

 too deadly. A process recommended in 1872 by Petit for the destruc- 

 tion of the phylloxera gave no result. 



85. Silver Chloride, AgCl. — Preparation. — By precipitating a 

 solution of silver nitrate by a solution of common salt, a white curdy 

 precipitate forms, soluble in ammonia and hyposulphite of soda. 



Properties. — Silver chloride is insoluble in water. Its properties 

 are the same as those of the nitrate, that is to say, it decomposes 

 readily in light and in presence of organic substances. 



Use. — PeronosjJora viticola, De By. (mildew of the vine). — Pauli 

 advised a mixture of silver chloride and hyposulphite of soda tinted 

 with eosin, and sold as "Puknos," against the cryptogamic diseases of the 

 vine, tomatoes, potatoes, rose-trees, and fruit-trees. The good anti- 

 cryptogamic effects produced in general have been observed in a large 

 number of vineyards treated. Unfortunately the use of this solution 

 was followed, especially after great heat, by serious burning of the 

 leaves. Its two components being too toxic for plants the use of 

 " Puknos " was abandoned. 



