INORGANIC POISONS 243 



The deep blue liquor obtained by adding ammonia to 

 copper sulphate contains the compound CuSO^NH^.H^O 

 called cuprammonium sulphate. When dried on the leaves 

 of the plants to which it has been applied by spraying, some 

 of the ammonia is evaporated and ammonium sulphate 

 and basic copper sulphate is left behind. The ammonium 

 sulphate washes off with ease and the basic copper sulphate 

 does not possess the same power of adhesion that is to be 

 found in the lime and soda varieties of basic copper sprays. 



Arsenic. White arsenic, arsenious acid, As 2 O 3 , is 

 used in sheep dips. From 2-10 Ibs. of sulphur, i Ib. of 

 arsenic and J Ib. of washing soda are ground up. The 

 washing soda may be replaced by " dry soap," a mixture 

 of soap and soda. The mixture rather improves on keeping, 

 as the arsenic slowly combines with the soda to form arsenite 

 of soda. The quantity stated makes 50 galls, of dip. 

 Whilst any sunk bath might be made to serve, special 

 dipping baths are on the market which are very economical 

 to use both as regards material and labour. Sodium arsenite 

 slowly oxidizes to sodium arsenate. Sunlight, aeration and 

 the presence of water increases the speed of the reaction. 

 Very old dips containing soda and arsenic may, therefore, 

 be partly oxidized to arsenate. As the arsenates are less 

 poisonous than the arsenites, old dips may have less value 

 than new ones. It is for this reason that a mixture of sodium 

 carbonate and arsenious acid is better than ready-made 

 sodium arsenite, as it takes much longer to deteriorate. 



Lead Arsenate. A very effective and safe remedy for 

 caterpillar attacks is a spray of J or % lead arsenate. 

 To prevent scorching the leaves of fruit trees, it is essential 

 that no marked excess of either lead or arsenic acid should 

 be present. As all the materials used are of varying compo- 

 sition and very poisonous, it is better to have the lead 

 arsenate in the form of a paste that can readily be diluted. 



Arsenious acid can be oxidized by nitric acid or, in the 

 presence of water, with chlorine. Sodium arsenate can be 

 then prepared and crystallized. The resulting crystals consist 

 of Na 2 HAsO 4 .7H 2 O ; but if crystallized at low temperatures 



