6 farmers' bulletin 603. 



A by-prtxluct of the actiou of sodium carboiuite uu white arsenic is the gas 

 (•arbon dioxid. The esoajie of this gas is attended by considerable fonniing 

 of the solution, so the kettle must be generously large, and the oiieratiou of 

 boiling must have c<»nstiinl wateliing to prevent the liquid from frothing over 

 the edge of the kettle. 



The kettle or tank, utensils, and materials must be perfectly free from all 

 greasy or oily substances, since a small quantity of such matter is sufficient li> 

 form a coating over the arsenic and thus to prevent or delay its solution. 



The boiled dip may be made perfectly well with very hard water, but. in 

 that case, some residue of a fine white or gray powder will be left undissolved 

 after boiling. This residue carries no arsenic, but arises from the action of the 

 sodium carbonate upon compomids, chiefly of lime, in the water. Examination 

 of the liquid after boiling for a few minutes with the soda before the arsenic 

 has been added will show how much residue may be expected from this source. 



MAKING THE S-B DIP.' 



The S-B arsenical dip was developed by the present -writer about 

 two years ago to meet certain drawbacks to the boiled dip, namely, 

 (1) the necessity for boiling large amounts of liquid, and (2) the 

 impossibility of preparing highly concentrated stock solutions. 

 Bureau employees in the field have given the preparation a thorough 

 test in practical dipping. The difference between the S-B dip and 

 the boiled dip is merely in the formulas and methods of preparation, 

 the composition of the diluted baths used for dipping being prac- 

 tically 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. 



S-B arsenic stock requires the following materials ready to hand 

 before starting: 



Pounds. 



Caustic soda,^ at least 85 per cent pure, dry, granulated 4 



White arsenic, 99 per cent pure, in fine powder 10 



Sal soda,' crystals 1 10 



In a H-gallon kettle or metal * pail place the 4 pounds of caustic 

 soda, add 1 gallon of cold water, and stir with a stick until the caustic 

 soda is practically all dissolved. Without delay begin adding the 

 white 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 liquid begins to boil, stop stirring tmd let it cool slightly 

 before adding more arsenic. The secret of success is to work in the 

 arsenic fast enough to keep the solution ver\' hot — nearly but not 



^Abbreviated from " self boiled," the name beiug suKKestcd by the fact that the hcnt 

 nt'coKsary to proparc tho dip Is wliolly derived from chemlctil action between the raw 

 materials. 



-Or .''ij iionuds dry caubtie potuuh of eipial purity. 



^ Or 4 J pounds nionoliydrati'd sodium eariionnte. 



* 'Pile chendcals employed have no elTeel upon Iron. They will, however, actively cor- 

 rode zinc, tin, or Holder ; hence a sol(lere<l pall must be watched for leaks and Is far 

 Inferior to a aeamlesM pall, stamped from a sluKle sheet of Iron. A tinned pall Is pre- 

 ferri'd lo a t.'<ilvaid/ed one, but u plain Iron aeamlPHH pall or an iron kettle should lie 

 obtiilned If possllile. 



