RABBIT POISONS.

New Zealand Mail, Issue 1201, 8 March 1895, Page 6

RABBIT POISONS.

THE USE OF ARSENIC STRONGLY RECOMMENDED. By F. Weight, Lecturer in Materia Medica to the Technical College, Sydney.

During the past ten years the attention of chemists has been directed to the importance of discovering a safe and easily administered poison for the extermination of the rabbits which infest so many of our country districts. Experienced hands in rabbit destruc tion have tried many experiments with various vegetable and mineral poisons, and it is a remarkable fact that a poison which answers admirably in the hands of some men appears to fail in the hands of others; while an exterminator which has been largely and successfully employed in one colony has met with but little favour in another.

Let me briefly define what is required in order to meet the requirements of ; our squatters who are suffering from j the ravages of this pest. It is a poison, I rapid and certain in its action, easily obtainable, and at a low price, not • readily destroyed by the influence of the sun, or air, or water. It should have comparatively little taste or smell, and should be free from danger in manipulation. In enumerating the various poisons which have been employed let us first consider bisulphide of carbon and its application. Carbon bisulphide is a compound of sulphur and carbon, prepared by heating charcoal to redness in a suitable vessel and dropping upon it from time to time particles of sulphur, the air being excluded and proper means being adopted to condense the vapours arising from the combination. The result is that a heavy colourless liquid is produced from the combination of these two solids. This liquid has a specific gravity of 1‘269, has a very disagreeable odour, and is'very volatile, boiling at about 115 deg. F. This liquid produces heavy, inflammable vapours, and when poured down a rabbit burrow, it displaces the air and suffocates the animal. The first action of the vapour upon the animal is not dissimilar to chloroform, but it is impossible for a rabbit to breathe the fumes for more than a few minutes without causing its certain death. The drawbacks to the use of this substance are that in hot weather there is great loss by evaporation, the vapours are very explosive when mixed with the air, and the continual inhalation of air impregnated with even a small percentage of the vapour will in the course of a few months produce a serious derangement of the intellect of persons engaged in a distribution of the carbon in the rabbit burrows.

Among the schemes proposed, one inventor patented a process for generating arsenuretted hydrogen gas in the rabbit burrows." llis apparatus consisted of a squat bottle holding about a quart of dilute sulphuric acid. This was to be placed in the mouth of the burrow, and into it was to be inserted a rod of metal made of an alloy of zinc and arsenic. On contact with the acid the metal would be gradually dissolved, giving off arsenuretted hydrogen gas, one of the most deadly fumes known. Unfortunately this gas will «ot sink into the burrow (being lighter than the air), and it is much more probable that the would be “destroyer ” would poison himself than that he would poison the pests. Another man inquired if I could supply him with arsenide or cyanide of cacodyl, as he had a plan to place a bomb in the burrows which upon explosion would give off such poisonous fumes as to destroy all animal life in the neighbourhood But this plan was never tried, being highly dangerous and impracticable. A w'el 1 -known Wesleyan minister proposed to me the plan ol making a biscuit of ergot of rye and pollard, the object being to cause the premature birth of the young rabbits, and hence to diminish the rate of increase, but I pointed out to him that the great uncertainty of the result and the perishable nature of the poison proposed would prevent its effect being reliable and observable, and people always want to see some positive proof that the poison is efficacious, not merely in the case of a few animals in cages, but in the millions of wild rabbits which swarm over our back country. A farmer proposed the cultivation of the Stavesacre plant (Delphinium etaphisagrin ), and the use of the seeds as well as the herb as a food for rabbits, but the danger of poisoning other animals is a serious drawback from the employment of this plant. The use of phosphorus as a poison

: has been very largely and very success fully employed. At first the grain to be phosphorised was merely placed in a cylinder made of galvanised iron. Hot water and phosphorus were added, and thowhole were rotated together until the phosphorus was finely divided and spread over the outside of the grain. Phosphorus will notdissolve in water, it' will only melt under the hot water ; and as the water cools the agitation minutelydivides the phosphorus, and causes it to adhere to the outside of the grain. Nor can the poison penetrate into the grain to any extent. When phosphorised grain is exposed to the action of the sun and the air, the phosphorus' will rapidly oxidise and become inert. Some makers of phosphorised grain adopted a different plan—viz., they dissolved the poison in bisulphide 'of carbon, with which had been added a small quantity of fat or wax; this assists in the diffusion of the phosphorus over the grain, without the aid of hot water, and at the same time protects the phosphorus from the action of the air. The advantages were that dry instead of wet grain was used, and the product was less liable to become inert after it had been laid only a little while. A later method, which seems to be very efficacious, is to substitute bran or pollard for grain, and to treat the phosphorus with hot water as already described.

The process of dissolving phosphorus in carbon bisulphide is very dangerous, and unless great care is exercised the mixture will spontaneously take fire. But a modification of the two processes might be adopted which would combine the good features of both. Lard and phosphorus can be intimately mixed together by the aid of heat, and this mixture again may be diluted with meal in any proportion desired. Again the poisonous compound thus formed may be made specially tempting by the addition of aniseed or some of the tempting foods which rabbits are known to be partial to, and the baits will be greedily devoured. The poison which I think should answer the purpose better than any other is arsenic or its compounds. A gardener, who was troubled by the destruction caused by the pests, came to me for some arseniate of ammonia, and using this on cabbage leaves he quickly got rid of the rabbits. The advantages of arsenic over other poisons may be briefly summed up as follows : —Arsenic is a very cheap poison, and there is always a plentiful supply of it; although volatile, it is not readily so. It is less easily destroyed than other poisons, and hence arsenical baits may be exposed to the sun and air without their efficacy being diminished. But arsenic is sparingly soluble in water. This may, however, in some cases be an advantage, as the poison will not be dissolved by rain, and the baits may thus be made to resist all weathers. If, however, a soluble form is desired, arsenic may bo dissolved in washing soda or caustic soda solution, and in this form may be applied to anv material which may be deemed advisable Care should be taken not to use morealk ali tlianisjust enough to dissolve the arsenic, ay an excess of alkali renders the baits unnecessarily nasty, and the rabbit; will refuse to ('at more as soon as it has tasted the poison. Of late many inquiries have been addressed to me as to the possibility of employing prussic acid as an exterminator. The difficulties in. employing this poison are very great in consequence of the liability to decomposition when exposed to sunlight I recently prepared some biscuits emits ining 10 per cent of cyanide of potassium, thinking that this form would be moio stable than any other, but found that shortly after the biscuits became dry the prussic acid in them had all been decomposed into ammonia, and hence the baits were harmless.

The dangers arising from phosphorus are the liability of the substance to spontaneous combustion, and the fact that the workers with this substance are liable to necrosis of the lower jaw. The danger of bisulphide of carbon arises from the explosive nature of its vapours and the mental depression which it. produces upon those who inhale its fetid vapours for any length of time. But with arsenic the only danger arises from using the vessels for other purposes before they have been thoroughly cleansed; but with proper precautions and careful manipulation lam convinced that arsenic will be found the most stable and effective of all the poisons in the eradication of the l’abbits. —Sydney Mail.