USE OF DESTRUCTIVE AGENTS — PARIS GREEN. 401 



Siilpho-carhonaie of lioiass'mnu— This salt was prepared from impure bisulphide of car- 

 bon, obtained in Denver (and contaiuiog naphtha), and an alcoholic saturated solution 

 of hydrate of potassa. .When sufficiently dilute, so as not to be injurious to plants, I 

 think it is equally harmless to the insects. A strong solution (nearly saturated) causes 

 the locusts to fall over and apparently kills them, but in fifteen minutes they revive, 

 and in half an hour are able to hop off. A solution of 1 to 10 or 15 has to be repeatedly 

 applied to have any apparent efiect, and, as far as I could observe, this effect soou 

 disappeared. The strong solution is sure and speedy death to plants, and yet does not 

 appear to kill the insects, so that with a dilute solution, one sufficiently so not to hurt 

 plants, no good effect can be had. 



Naphthaline. — The impure specimens I was able to obtain at the gas-works in DeniiTur^. 

 which contain many impurities, do not warrant me in reporting upon the effeet: of 

 naphthaline as such. The effects I observed were far less satisfactory than tlliose. I , 

 obtained with coal-tar. Naphthaline, like bisulphide of carbon, can only work whea 

 kept in contact with the insects for some time. It gives off its vapors slowly,, and. is 

 not, therefore, capable of successful application where locusts are concerned. I have 

 watched a locust for three-quarters of an hour moving about over the impure naph- 

 thaline left in the oil-barrel by pouring out the oil (oil from coal-tar), whereaaS.a single 

 drop of the crude oil itself causes almost immediate death. 



The above and Paris green are the principal substances experimented with,, others 

 being counted out, either for the reason that they are applicable only to, the protec- 

 tion of i^lants against feeding insects which did not appear during my stay in Colorado ; 

 that their ineffectiveness is well known, or that chemical considerations (e. </, in the 

 case of sulphuric acid) forb id their use, or demonstrate its impracticability. 



lu conclusion, I will say that I am a witness of the speedy action of coal-oil upon 

 young locusts, an action which is certain and immediate. I have taken astraw, dipped 

 in the crude oil distilled from coal-tar, shaken off the pendent drop, and touched the 

 insects with the residue. Treated with this minute quantity they died in from eight to 

 ten minutes. I have seen substantially the same effect with kerosene. As^only a small 

 quantity of oil need be employed it is perhaps unnecessary to point out the difference 

 in price between kerosene and crude coal-tar oil, but the attention of farmers may use- 

 fully be drawn to the fact that such difference exists. They have, chemically speaking, 

 certainly discovered the cheapest and most effective remedy against the ravages of the 

 unwinged locusts. No known chemical is at once so deadly in its^ action and at the 

 same time so cheap as "coal-oil." Its manijpulation is simple aad unattended with 

 any danger which cannot be easily guarded against by a little care. This fact, together 

 with its comparative cheapness and freedom from danger of adulteration, are the ad- 

 vantages it possesses which recommend its use as an active poison. This point is, I 

 think, clearly settled. 



The other questions of protection to plants, and of the chemical value of the immense 

 quantities of locusts which annually die in the West, considered as fertilizers, as well as 

 the further question (interesting in a scientific point of view) as to what is the chemical 

 nature of those secretions of the mature locusts which are said to be deleterious to 

 fowls and even to affect the human skin, must as yet remain unanswered. 



The deadly effect on animal life of carbonic-acid gas is well known. 

 In 1875 we used it from a Babcock extinguisher, and gave it a thorough, 

 trial under many different circumstances and conditions, but without 

 any satisfactory results. It had very little effect upon them even when 

 played upon them continuously and at short distance. They often be- 

 came numbed by the force of the liquid, but invariably rallied again. 



Paris green. — This, though it kills those insects which partake of it, 

 is yet no protection to plants, because those which go off to die after 

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