36 



which has already been three-fourths filled with water, and stir 

 thoroughly. For a stock solution to be kept on hand and used when 

 needed, add no tar, but, after the solution of arsenic and soda has 

 become entirely cold, make it up to 25 U.S. gallons (20-82 Impl.), stir 

 well, let it settle, and draw off into containers which can be well closed. 

 This constitutes " low-strength boiled arsenic stock," and its use in a 

 diluted dipping bath calls for a " tar stock " prepared by dissolving 

 I lb. of dry caustic soda or concentrated lye (or 1 lb. of dry caustic 

 potash) in 1 U.S. quart of water, add 1 U.S. gallon of pine tar. and 

 stir thoroughly with a wooden paddle until the mixture, which at first 

 looks streaked and muddy, brightens to a uniform thick flmd 

 somewhat resembling molasses. A teaspoonful dropped into water 

 in a glass and thoroughly stirred should mix perfectly with the water. 

 Globules of tar seen by looking at the glass from underneath and which 

 cannot be blended with the water by repeated stirring, indicate that 

 more caustic soda solution is needed, and this should be added, not 

 more than a pint at a time, and with thorough stirring, until the desired 

 effect is produced. If a glass- vessel for making the test is not at hand, 

 a Httle of the mixture may be taken between the fingers, which should 

 then be dipped in water and the tar rubbed off. It should leave the 

 fingers perfectly clean after a Httle rubbing. If an oily coating remains, 

 more caustic soda solution is needed. The tar stock should be kept 

 in closed containers. High-strength boiled dip or stock is prepared 

 in the same way as the low-strength, except that 25 lb. of washing, 

 soda and 10 pounds of arsenic are used for 500 U.S. gallons of high- 

 strength bath. The " self-boiled " arsenical dip was devised in order 

 to meet certain drawbacks to the boiled dip, namely : ( 1 ) The necessity 

 for boihng large amounts of hquid and (2) the impossibihty of preparing, 

 highly concentrated stock solutions. It has been so named owing to 

 the fact that the heat necessary to prepare the dip is wholly derived 

 from chemical action between the raw materials. It has been 

 thoroughly tested in practical dipping in the field and differs from 

 the boiled dip merely in the formulae and methods of preparation, the 

 composition of the diluted dipping bath being practically the same 

 in both cases. The S.-B. dip is prepared in two parts, which must not 

 be mixed except in the diluted dipping bath : (1) arsenic stock, (2) 

 tar stock. The tar stock is prepared as stated above. To prepare 

 S.-B. arsenic stock the following materials are required : Caustic soda, 

 at least 85 per cent, pure, dry, granulated, 4 lb. (or 5| lb. dry caustic 

 potash of equal purity) ; white arsenic, 99 per cent, pure, in fine 

 powder, 10 lb. ; washing soda, crystals, 10 lb. (or 4| lb. of mono- 

 hydrated sodium carbonate). In a 5-gallon kettle or metal pail, place 

 the 4 lb. of caustic soda, add 1 U.S. gallon of cold water, and stir with 

 a stick until the soda is practically all dissolved. Without delay 

 begin adding the arsenic, in portions of a pound or two at a time, as 

 fast as it can be dissolved without causing the solution to boil, stirring 

 all the time. If the hquid begins to boil, stop stirring and let it cool 

 shghtly before adding more arsenic. The secret of success is to add 

 the arsenic fast enough to keep the solution very hot — nearly, but not 

 quite at the boihng point. The result should be a clear solution. 

 If the hquid persistently remains muddy or milky, it may be because 

 the operation has been conducted so fast that much water has been 

 boiled out and sodium arsenite is beginning to crystalhze, in which case- 



