MATERIALS 51 



separated as soon as the soft soap is destroyed ; but 

 this separation is often prevented to a greater or less 

 extent by the presence of minute solid particles in 

 the liquid, these being themselves capable of produc- 

 ing cmulsification. This is the reason why, when a 

 caustic emulsion is made with soap (10^), the results 

 vary with the character of the particular soap used, 

 rendering it advisable always to use a soap specially 

 prepared for the purpose. 



Soft soap by itself possesses considerable insecticidal 

 properties, partly due to the free alkali and glycerin 

 present in it, and partly to its blocking up the breath- 

 ing apparatus of insects. It is too feeble in its action, 

 however, to be of any use, except for summer spray- 

 ing, and, even then, it is generally better to supplement 

 the action of the soap by adding to it some more 

 deadly material, such as paraffin {i. e. using an emul- 

 sion), or nicotine or quassia, in cases where paraffin 

 would do harm — e.g. in the case of hops, roses, etc. 



When soft soap is used alone, the proportions taken 

 may be varied between i and 5 lbs. to every 10 gallons 

 of water. Soft water should be used, as hard water 

 destroys some of the soap, converting it into an 

 insoluble calcium soap. 



For the same reason, soap should never be mixed 

 with insecticides containing lime or other mineral 

 substances : potassium sulphide is the only mineral 

 insecticide which will not decompose it. 



18. Sodium cJiloride i^Coimnon salt). — This is never 

 used by itself as an insecticide, but it forms one of 

 the constituents in the lime-salt wash already men- 

 tioned under 12, and in other washes described below. 



