Suppose a room to be 12 by 15 by 8 feet. It will contain 12 × 15 × 8, or 1440 cubic feet. For convenience the writer always works on the basis of complete hundreds; in this case he would work on the basis of 1500 cubic feet, and thus be sure to have enough. The foregoing room, then, would require 15 ounces of cyanid, 15 ounces of sulfuric acid, and 45 ounces of water. The room should be made as tight as possible by stopping all the larger openings, such as fireplaces and chimney flues, with old rags or blankets. Cracks about windows or in other places should be sealed with narrow strips of newspaper well soaked in water. Strips of newspaper two or three inches wide that have been thoroughly soaked in water may be applied quickly and effectively over the cracks around the window sash and elsewhere. Such strips will stick closely for several hours and may be easily removed at the conclusion of the work. While the room is being made tight, the ingredients should be measured according to the formula already given. The water should be measured and _poured first_ into a stone jar for holding at least two gallons. The jar should be placed in the middle of the room, with an old rug or several newspapers under it in order to protect the floor. The required amount of sulfuric acid should then be poured rather slowly into the water. _This process must never be reversed; that is, the acid must never be poured into the jar first._ The cyanid should be weighed and put into a paper bag beside the jar. All hats, coats, or other articles that will be needed before the work is over should be removed from the room. When everything is ready the operator should drop the bag of cyanid gently into the jar, holding his breath, and should walk quickly out of the room. The steam-like gas does not rise immediately under these conditions, and ample time is given for the operator to walk out and shut the door. If preferred, however, the paper bag may be suspended by a string passing through a screw eye in the ceiling and then through the keyhole of the door. In this case the bag may be lowered from the outside after the operator has left the room and closed the door. The writer has most often started the fumigation toward evening and left it going all night, opening the doors in the morning. The work can be done, however, at any time during the day and should extend over a period of five or six hours at least. It is said that better results will be obtained in a temperature of 70° F., or above, than at a lower degree. At the close of the operation the windows and doors may be opened from the outside. In the course of two or three hours the gas should be dissipated enough to allow a person to enter the room without danger. The odor of the gas is like that of peach kernels and is easily recognized. The room should not be occupied until the odor has disappeared. FUMIGATING A LARGE HOUSE