On opening the lid of the biscuit-tin containing the ammonia and pill-boxes, be careful to keep your face well away, or the puff of vapour may be very painful. There is no danger whatever to be feared from the use of ammonia in this manner, but still it may lead to temporary discomfort, such as pain in the eyes and loss of breath for a moment.
Having removed the lid proceed in the following manner: First place on the table before you a sheet of white paper or a blotting-pad. By your side on the table have a small tea-tray, or other flat receptacle. Take out of the tin one of the top pill-boxes, open the lid, and shake out the butterfly on the sheet of paper in front of you. Then put the lid of the pill-box with its top turned downwards, on the tea-tray, and place the remainder of the pill-box, _sideways_ within the lid. The object is to let the air get to the inside of the boxes, so as to evaporate the ammonia still remaining about them, or the next butterfly to occupy the box will object to the stale fumes of "smelling salts," and probably knock itself about in consequence. The boxes may be thus all emptied and left to air, which will not require much more than an hour, or even less, if the tray be placed in the sunshine near an open window. By placing each box sideways in its lid, the boxes and lids all fit one another, and do not get tiresomely mixed.
In shaking out the butterflies place them in rows neatly on the paper, so that you know which was the first to leave the boxes, for that row should be the first pinned, having been exposed longer to the fresh air, to permit the ammonia attached to them to evaporate. If pinned too soon, the ammonia is apt to affect the metal of the pin and make it brittle where it passes through the body of the insect. The action of this gas is most peculiar on the colours of some insects, especially on that of the small heath butterfly, marbled whites, or some of the blues. When seen for the first time one is horror-stricken, and apt to exclaim that the specimens are ruined with the nasty stuff. This, however, soon all passes away as the ammonia evaporates and the normal colours reappear in all their former beauty. Some collectors rail against ammonia, using themselves some worse killing medium. There is no other such medium which will allow of one, after pinning the insect, to move it up and down quickly in the air with the effect that the wings are as flaccid as though the specimen were alive. It leaves not the slightest trace of rigidity, which is of the highest importance for quick and successful setting out.