Next to the 'cyanide,' the bruised laurel takes the first rank for permanency; but you must not expect this to last many days. For a few days' continuous work one charge will suffice, but if the laurel box has not been in use for some time you must have a fresh supply. The liquid poisons, such as ammonia, chloroform, and benzole, are so volatile that they are very powerful for a short time, but so much vapour is lost each time the box is opened that it is absolutely necessary to carry a bottle of the one you use into the field with you. Also see that you have sufficient of the blotting paper or other absorbent to prevent the liquid from leaking through the perforations of the partition. If you choose ammonia--a substance that is not regarded as a poison, and is therefore easily obtained from any chemist--always get the strongest, and see that it is labelled 'Liq. Ammonia, S.G. .880' as a guarantee. A small bottle such as you can conveniently carry in the waistcoat pocket will contain sufficient for a day's work. Use only a few drops at a time, but renew frequently. Although the ammonia corrodes cork, yet a good cork is far preferable for the pocket to a glass stopper, for its elasticity prevents it from losing its hold, and the liquid from saturating your pocket and its surroundings; but a glass stopper is certainly better for the stock solution kept at home. Most of the above remarks apply equally well to benzole and to chloroform, but the latter is so powerful a poison that a very little is required for a day's work, and consequently a very small bottle is more convenient. The dealers in naturalist's appliances supply metal 'chloroform bottles' with screw stoppers and a small nozzle that will allow the liquid to run out only in drops. This is a very good arrangement, since it enables you to avoid the 'drop too much' which is not only unnecessary and therefore wasteful, but saves you from experiencing the disappointment of an empty bottle before your work is half done. [Illustration: FIG. 45.--THE CHLOROFORM BOTTLE.] Some entomologists recommend the solid carbonate of ammonium instead of liquid ammonia, but this is not so powerful. It must be remembered that we have the butterflies to consider, as well as our own convenience, in the selection of the poisons we use. It is the opinion of many well-known entomologists that 'insects cannot feel pain,' and that we are therefore at liberty to deal with them in any way we please. Still it is as well to save all possible suffering, and be satisfied with no killing box that is not practically instantaneous in its effects.