INSECTICIDES, PREVENTIVES, AND MACHINERY. 447 



clogging the spiracles, and so choking the insects. It follows 

 that, as a rule, only those insects with exposed openings can be 

 reached, and that the application must be so made as to cover 

 completely. Soaps that are sticky and lather freely, leaving a 

 scum when dry, are better than those that are clean. Therefore, 

 fish-oil soaps are more useful than those made from animal fats. 

 Sometimes soaps serve only as carriers for petroleum, quassia, 

 tobacco, or carbolic acid ; but more usually only enough of such 

 materials is added to give a distinct odor, and nothing is gained 

 except a larger price by the makers. 



There are several good fish-oil soaps on the market, — usually 

 called whale-oil, though there is no whale-oil in them, — and 

 these, whether emulsified with soda or potash, .sell for from two 

 and one-half to five cents per pound according to the quantity 

 ordered ; in single pound lots for even a higher price. At a 

 strength of from one pound in four to one pound in six gallons of 

 water they reach most plant-lice and larval scales. One pound 

 in six is usually the extreme dilution that is effective against in- 

 sects, and when stronger it becomes necessary to watch for injury 

 to foliage. Mature foliage suffers less than such as is immature, 

 and in late summer most fruit trees will stand one pound in one 

 or two gallons when it is necessary to check scale development. 

 A very satisfactory soap can be made according to the following 

 formula, first suggested by the New York (Geneva) Station : 



Caustic soda, 75 per cent, or over 6 pounds 



Water 6 quarts 



Fish-oil 22 pounds 



Dissolve the caustic soda in warm water until it is thoroughly 

 fluid ; then pour in the oil slowly, stirring thoroughly and con- 

 stantly until the combination is complete. Complete and thor- 

 ough stirring is essential to success, and the oil should be warmed 

 to eighty degrees Fahrenheit, or thereabouts, so as to make it 

 thoroughly fluid before adding to the soda solution. Almost any 

 kind of fish-oil will answer, and the amounts above given will make 

 about forty pounds of soap. For smaller quantities, one-sixth of 

 the amount may be used, and one pint of oil may be reckoned as 

 a pound. This makes a cheesy mass when cold and is stronger 

 than the commercial article, so that one pound in seven gallons 

 of water will do as well as one pound in six gallons of the latter. 



