2. A cork that will fit the bottle tightly and is long enough to handle easily. 3. Two cents' worth of cyanide of potassium. 4. One cent's worth of plaster of Paris. These latter materials may be procured from any drug store. Place the lump of cyanide of potassium in the bottle and pour in enough water to cover it. Add immediately enough plaster of Paris to soak up all the water; leave the bottle open in a shady place for an hour and then wipe the dry plaster of Paris from its sides, put in the cork, and it is ready for use. The plaster of Paris forms a porous cement, which, while it holds the cyanide fast in the bottom, also allows the fumes of the poison to escape and fill the bottle. It should be labelled "poison," for cyanide of potassium is very poisonous. If kept corked when not in use, a killing bottle made like this will last a whole season. The first rule in using the killing bottle is this: do not kill any more insects than you need for your collection. The second rule is: do not breathe the fumes of the bottle, for they smell badly and are not good for you. When you uncork the bottle to put an insect in it, hold it away from your face and cork it up again as quickly as possible. Some insects may be caught from flowers, etc., directly into the bottle by holding it uncorked beneath them for a moment; the fumes of the poison soon overcome them and they drop into the bottle. In taking insects from the net, hold the bottle in the right hand and the cork in the left; insert the bottle into the net and place the mouth of it over an insect crawling on the inside of the net, then put the cork on the outside of the net into the mouth of the bottle, net and all, for a moment until the insect falls into the bottom of the bottle; then remove the cork and take the rest of the imprisoned insects in the same way. Insects should be left in the bottle at least an hour, and may be left in there over night without injury to the specimens. INSECT PINS. FIG. 130. [Illustration: _Fig. 130. Insect pins, 1, 3, 5, are German insect pins. 2 is a steel mourning pin._] After the insects are caught they should be pinned so that they may be arranged in the collection in an orderly manner. Common pins are not good for pinning insects; they are too thick and they corrode very soon, covering the specimens with verdigris. Regular insect pins are desirable as they are very slender and do not corrode so quickly. These may be obtained of any dealer in entomological supplies at a cost of fifteen cents per hundred. Ask for the German insect pins Nos. 1, 3 and 5. If these pins are too expensive you can use the black steel mourning pins. These come in shallow boxes one by two inches square and have round glass heads and the boxes are labelled "Germany;" these may be procured from any dry goods store. However, insects pinned with any beside regular insect pins cannot be sold or exchanged.