480 FRUIT INSECTS 



and should be used in place of them upon ripening fruit. It is 

 used for various leaf-eating insects, particularly for the currant 

 worm and rose slug. 



Soaps 



Soap solutions are often used as contact insecticides for kill- 

 ing plant-lice and other small, soft-bodied insects. The so- 

 called whale-oil or fish-oil soaps are most widely used for this 

 purpose. The commercial brands are usually by-products 

 from the manufacture of other products, and contain many 

 impurities; furthermore, many of them contain an excess of 

 free or uncombined alkali and are consequently very likely to 

 injure young and tender foliage. An excellent fish-oil soap may 

 be easily prepared at home by the following formula : 



Caustic soda 6 pounds 



Water | gallon 



Fish-oil 22 pounds 



Completely dissolve the caustic soda in the water, and then add 

 the fish-oil very gradually under constant and vigorous stirring. 

 The combination occurs readily at ordinary summer tempera- 

 tures and boiling is unnecessary. Stir briskly for about twenty 

 minutes after the last of the oil has been added. 



A good insecticide soap can be prepared in a similar way from 

 cotton-seed oil soap-stock or from the more impure grade 

 known as pancoline. In fact, there is on the market a good 

 insecticide soap made from similar materials. 



Sulfur 



Sulfur is commonly sold in two forms, — flowers of sulfur and 

 flour of sulfur. Flowers of sulfur or sublime sulfur is a fine, 

 impalpable yellow powder insoluble in water, and is formed by 

 condensing sulfur vapor in a large chamber of brick work. If 

 the sulfur vapor is condensed to the liquid form in a cold re- 



