MATERIALS 33 



weight of " crude " potash, that is, of potassium car- 

 bonate or potashes : this is a great mistake ; as the 

 carbonate has little or no detergent or insecticidal 

 value, and the use of it means so much waste of 

 money, and a reduction of the strength of the wash 

 below that at which it is efficient. 



The efficiency of a caustic winter wash as an in- 

 secticide has been found to be much increased by the 

 addition of paraffin, and such mixtures are to be re- 

 commended in preference to the simple caustic wash. 

 The mixture is known as the Woburn Wash. The 

 substances used for incorporating the paraffin with 

 the soda are either soap, basic sulphate of copper, or 

 basic sulphate of iron. 



When soap is used attention should be paid to the 

 brand, for with some soaps the addition of soda will 

 cause the entire separation of the paraffin, and with 

 others, the soap will separate in big clots, which clog 

 the nozzles of the machines. The Chiswick Soap Co. 

 sell a brand (The Woburn Soap) specially adapted for 

 the purpose. The recipe for this waste is — 



(10/;) Soft soap . . . \\h. 



Paraffin (solar distillate). 5 pints. 



Caustic soda . . . 2 to 2J lbs. 



Water .... 9^ galls. 



Dissolve the soap in the water (hot or cold) : churn 

 the paraffin up with it (p. 46), and then shake the 

 soda into it. 



The soda converts the soft soap (potash soap) into 

 hard soap (soda soap), and this, together with the 

 paraffin, tends to rise to the surface, so that the 



