INSECTICIDES, PREVENTIVES, AND MACHINERY. 435 



The advantages of the home mixtures are their low cost and 

 their known strength. If carefully made, they are always uniform 

 in composition and similar effects may be expected from similar 

 applications. Care in securing a proper combination is essential ; 

 otherwise serious injury is certain to result. 



Paris green is the most widely used of all the arsenical poisons, 

 and is a combination of arsenious oxide, about sixty-eight per 

 cent. , with copper oxide, about thirty per cent. The percentage 

 of arsenic may range from fifty to seventy without necessarily 

 proving adulteration ; but carelessness in the manufacture may 

 make a product unreliable, and may lead to material differences in 

 effect on foliage as well as insects. In its usual form Paris green 

 is crystallized, and the size of the particles has a great influence 

 upon its effect. When coarse, they sink readily, necessitating 

 constant stirring, and are unevenly distributed on the leaves ; 

 when fine, they remain in suspension longer and spread more 

 evenly on the sprayed surface. Only a small percentage of the 

 arsenic is soluble, and at strengths ordinarily used no addition of 

 lime is necessary ; but when the mixture is strong and the sun is 

 hot it will be better to add one pound of lime to each pound of 

 green, slaking the lime to a thin wash and then adding the 

 poison, which is better first made into a thin paste with just 

 enough water to do so. 



As Paris green is the most generally used material, all others 

 must compare with it in the amount employed. Against young 

 larvae and most slugs one pound in two hundred gallons of water 

 is effective ; but so great a dilution is rarely used except on sensi- 

 tive foliage. On peach this poison should never be used at all. 

 As against codling-moth, one pound in from one hundred and 

 fifty to one hundred and seventy-five gallons of water is used, and 

 that forms a good average strength for most leaf-feeding insects, 

 rarely injuring the foliage unless used in excess or allowed to 

 settle so as to make the sprayed solution irregular in its effect. 

 On potato beetles, one pound to seventy-five gallons is usually 

 effective, but some farmers use it at the rate of one pound in fifty 

 gallons, or even stronger, and claim good results as well as safety 

 to foliage. 



Crystallization of Paris green is not necessary to its usefulness 

 as an insecticide, but a positive detriment, because it increases 

 the weight of the particles and the cost of making. There has 



