154 REPORT 4, UNITED STATES ENTOMOLOGICAL COMMISSION. 
SULPHUR. 
A machine for the application of the vapor of this mineral is described 
in Chapter XIII ; but, so far as we can see, the machine has not been used 
to any extent. Nor is it probable that sulphur vapor will destroy the 
worms, when applied in the open air. 
RED LEAD. 
The following account of experiments with this substance is from Mr. 
Schwarz's report : 
At the suggestion of Professor Barnard I made a few experiments with red lead. 
September 4 I dnsted five worms slightly with the powder and placed them in a glass 
jar together with a few fresh leaves. No effect visible after twenty-four or forty- 
eight hours. Placed a few worms in a glass jar and fed them with leaves thickly 
dusted with red lead. After eight hours no effect visible, but the worms did not seem 
to have eaten of the leaves. After twenty-four hours three of the worms were dead, 
two others showed the col'or peculiar to those poisoned by Paris green or London 
purple and died in the course of the day. 
September 19. — Red lead diluted with five parts of flour and the mixture thrown on 
some plants which were fairly alive with young worms. Twenty-four hours after- 
wards some poisoned worms were found ; thirty-six hours after application some more 
dead worms, but in the mean time most of the mixture had been washed away by a 
heavy rain,' and the remaining worms were sufficient to defoliate the plants. I fully 
believe, however, that this mixture would have been efficient to protect the plant if 
the rain had not interfered. 
September 22. — Applied a mixture of one part red lead to ten of flour. Within 48 
hours I noticed a few dead young worms, presumably killed by the poison, but most 
of the worms were not affected, or, if so, not seriously affected. I had no further op- 
portunity to experiment with this substance, but do not believe it can be advanta- 
geously used as a substit ute for Paris green or London purple, as it evidently does not act 
so powerfully as either of the two. Further experiments are, however, necessary to 
obtain a definite opinion regarding its value as an insecticide. Its price (so far as I un- 
stood) is cheaper than Paris green, but more expensive than London purple. Its 
value as an insecticide will, of course, depend also upon its influence on the plant, a cir- 
cumstance to which I omitted to pay attention, though there was certainly no marked 
injurious influence in my experiments. 
ROAD DUST AND ALLIED SUBSTANCES. 
The protection from the attacks of the worm and the prevention of 
the ovipositing of the moth accomplished by thickly dusting the leaves 
on both sides has already been mentioned on page 126. It still remains 
here to speak of the property of road dust to drive off or kill the worms. 
If a powerful jet of water is directed on the soil at the base of the plant 
so as to splash the softened mud on the lower leaves, the worms on 
them will be covered with the soil and many of the young ones are 
unable to remove it. They fall to the ground and exhaust themselves 
in frantic and fruitless efforts to clean themselves. The same result can 
be accomplished by throwing dry dust on the plant during or shortly 
after rainy weather, or after the plants have been thoroughly wetted 
with a sprinkler. 
Not every kind of dust is suitable for this purpose, and for utilizing 
