INORGANIC POISONS 245 



Zinc Chloride. The process commonly called " Burnet- 

 tizing " from the name of the inventor, consists in preserving 

 timber by a 2 % solution of zinc chloride, forced in under 

 pressure. A strong solution of 50 % of zinc chloride is made 

 by dissolving scrap zinc in hydrochloric acid and evaporating 

 to a density of 1-56. The excess of hydrochloric acid is 

 given off and may be condensed. This strong solution can 

 be diluted as required. 



Potassium and Sodium Permanganate. These dis- 

 infectants work by oxidation. They are made by heating 

 the carbonate of the appropriate alkali metal with manganese 

 dioxide and some oxidizing substance such as potassium 

 chlorate or potassium nitrate. The mass is boiled with 

 water and enough acid added to turn the solution pink. 

 The solution is then crystallized. Potassium permanganate 

 is easier to crystallize than the corresponding sodium salt 

 The permanganates can also be made electrolytically. 



Barium Carbonate. This insoluble substance occurs as 

 a mineral and only requires grinding. Ten parts of barium 

 carbonate, 10 parts of sugar, 10 parts of oatmeal and 

 i part of aniseed, make a good poison for rats. The poison 

 should be placed where dogs, hens and pheasants are not 

 likely to find it. Barium carbonate is insoluble in saliva, 

 but dissolves readily in gastric juice. 



Alkali Salts. Potassium and sodium nitrates are used 

 in pork pickle. Sodium chloride is a well-known weed 

 killer. The purity of the salt for weed killing is of no 

 consequence. 



Sodium bicarbonate is used sometimes in butter 

 manufacture. When only a few cows are kept at a farm, 

 cream is allowed to accumulate for a few days before churning. 

 In summer weather the cream so stored may be over-ripe, 

 butter be difficult to make satisfactorily and the product 

 be rancid to taste and smell. The bitter flavour and rancid 

 smell are due to butyric and other similar acids. Butyric 

 acid is more soluble in fat than in water, hence washing 

 with water only removes it slowly. If, however, sodium 

 bicarbonate be added, sodium butyrate is formed which is 



