1902.] DISEASES AND INSECTS, ETC. I43 



Paris green long- held front rank as an arsenical insecti- 

 cide. It is decidedly more expensive than other arsenical 

 poisons, and some of these are now being substituted for it in 

 many places, and in increasing quantities. Prominent among 

 these may be mentioned a green arsenite of copper which 

 represents about the same amount of arsenous oxide as 

 Paris green, and is used pound for pound in place of that 

 substance as an insecticide. It has the advantage of being 

 much cheaper than Paris green, and it is also better adapted 

 for use in a spray mixture, because, 1:)eing an amorphous, im- 

 palpable powder instead of crystalline, it stays much longer in 

 suspension in liquid mixture than does Paris green. 



A good many of you can remember back to the time when 

 the potato beetle started from its home in the Rocky Moun- 

 tains and commenced its travels across the intervening 

 stretch of territory 1,800 miles to the Atlantic coast. You 

 will remember how its progress was heralded from time to 

 time. I remember well the first specimens that were passed 

 around. The farmers were very much alarmed, and naturally 

 so, but it resulted in putting into our hands Paris green as 

 an insecticide against leaf-eating insects generally, and from 

 the use of Paris green we have passed to the use of other 

 arsenical poisons, and so from what appeared at that time to 

 be a calamity has come a blessing, as has been shown over and 

 over again in our experiments. 



I have already spoken of the green arsenite of copper, but 

 there is a still cheaper and equally efficient arsenical insecti- 

 cide in a homemade preparation of sodium arsenite. It is 

 made by boiling white arsenic in sal soda (sodium carbonate) 

 until it dissolves. It may then be bottled or otherwise kept 

 from evaporating, and may be used in all formulae in place 

 of Paris green. So much of the liquid as represents one 

 pound of white arsenic is taken in place of two pounds of 

 Paris green. Milk of lime should be added to prevent injury 

 to the foliage unless it is combined with Bordeaux mixture. 



The experiments of the Massachusetts gypsy moth com- 

 mission have established arsenate of lead as one of the most 

 desirable of arsenical insecticides. It is less liable to injure 

 the foliage than Paris green. Its color is such that it shows 

 plainly where it has been applied. It remains in suspension 

 in water so well that there is no difficulty in applying it at uni- 

 form strength. 



