442 SANITARY ENTOMOLOGY 



animals are to be treated, or if complete destruction of ticks is to be 

 accomplished. 



Dipping vats of various designs and built of several kinds of material 

 have been utilized. The size of course is dependent somewhat on the num- 

 ber of animals to be treated. The question of vat construction is dis- 

 cussed in several bulletins of the Department and these should be consulted 

 by those contemplating vat building. 



In the early days of tick control work crude petroleum was utilized 

 almost entirely against the cattle tick, but this had many disadvantages. 

 At present arsenicals are relied upon exclusively. These consist of either 

 sodium or potassium arsenite. The usual formula used in making up 

 the dip is as follows: Sodium carbonate (sal soda) 24 pounds, arsenic 

 trioxide (white arsenic) 8 pounds, pine tar one gallon, and water to make 

 500 gallons. Under certain conditions a stronger dip, consisting of 25 

 pounds of sal soda and 10 pounds arsenic, is used. A concentrated or 

 stock solution is made by dissolving the sal soda in about 25 gallons of 

 water, adding the white arsenic and boiling until it is all combined ; then 

 after cooling the dip to about 140° F. the pine tar is slowly added while 

 stirring. 



Several modifications of this dip and methods of making it have been 

 introduced, among them the addition of caustic soda to produce the com- 

 bination of the arsenic and sal soda without boiling. The self-boiled 

 dip is prepared in two parts which should not be combined except in the 

 diluted condition in the vat. These are the arsenic stock and the tar 

 stock. The arsenic stock is made as follows: Caustic soda (at least 85 

 per cent pure, dry, granulated) 4 pounds, white arsenic (99 per cent 

 pure) 10 pounds, sal soda (crystals) 10 pounds. In a large metal con- 

 tainer place the 4 pounds of caustic soda, add one gallon cold water and 

 stir until the caustic is practically all dissolved. Immediately begin add- 

 ing white arsenic, a pound or two at a time as fast as it can be dissolved 

 without causing boiling. If the mixture begins boiling stop stirring and 

 cool slightly before adding more arsenic. If the proper kind of chemi- 

 cals are used a clear solution, except for dirt, should result. When the 

 solution is cool add cold water to make 5 gallons. This stock solution 

 may be uspd immediately or kept indefinitely. The tar stock is prepared 

 by dissolving % of a pound dry caustic soda in 1 quart of water, add 

 1 gallon pine tar and stir until a uniform fluid resembling molasses 

 results. It should mix perfectly with water. In filling the vat, first add 

 the necessary amount of water then add the concentrated dip in a thin 

 stream in various parts of the vat. The tar stock should be mixed with 

 several times its volume of water before being added to the vat. Stir the 

 mixture in the vat thoroughly. 



Another modification of this dip which should be mentioned is the 



