This section is from the "Henley's Twentieth Century Formulas Recipes Processes" encyclopedia, by Norman W. Henley and others.
(See also Turpentine.)
Poisons for rats may be divided into two classes, quick and slow. Potassium cyanide and strychnine belong to the first, and phosphorus and arsenic to the second. Both should be kept away from children, dogs, and cats, and this is best done by putting them in places too narrow for anything larger than a rat to squeeze into. If the poison is too quick, the effect of it is visible to the same rats which saw the cause, and those which have not eaten of the bait will leave it alone. On the other hand, if it is too slow, the poisoned rat may spread it to edible things in the pantry, by vomiting. Slow poisons generally cause the rat to seek water, and when they are used water should not be left about promiscuously.
The substances most useful as rat poisons, and which are without danger to the larger domestic animals, are plaster of Paris and fresh squills. Less dangerous than strychnine and arsenic are the baryta preparations, of which the most valuable is barium carbonate. Like plaster of Paris, this substance, when used for the purpose, must be mixed with sugar and meal, or flour, and as a decoy some strong-smelling cheese should be added. In closed places there should be left vessels containing water easily accessible to the creatures.
One advantage over these substances possessed by the squill is that it is greedily eaten by rats and mice. When it is used, however, the same precaution as to water, noted above, is necessary, a circumstance too frequently forgotten. In preparing the squill for this purpose, by the addition of bacon, or fat meat of any kind, the use of a decoy like cheese is unnecessary, as the fats are sufficiently appetizing to the rodents. It is to be noted that only fresh squills should be used for this purpose, as in keeping the bulb the poisonous principle is destroyed, or, at least, is so modified as to seriously injure its value.