The gas is generated from the salt potassium cyanid, by treating it with sulfuric acid diluted with water. Potassium cyanid is a most poisonous substance and the gas emanating from it is also deadly to most, if not all, forms of animal life. The greatest care must always be exercised in fumigating houses or rooms in buildings that are occupied. Before fumigation a house should be vacated. It is not necessary to move furniture or belongings except brass or nickel objects, which may be somewhat tarnished, and butter, milk, and other larder supplies that are likely to absorb gas. If the nickel and brass fixtures or objects are carefully covered with blankets they will usually be sufficiently protected. There may be danger in fumigating one house in a solid row of houses if there is a crack in the walls through which the gas may find its way. It also follows that the fumigation of one room in a house may endanger the occupants of an adjoining room if the walls between the two rooms are not perfectly tight. It is necessary to keep all these points in mind and to do the work deliberately and thoughtfully. The writer has fumigated a large college dormitory of 253 rooms, once a year for several years, without the slightest accident of any kind. In order to fumigate this building about 340 pounds of cyanid and the same amount of sulfuric acid were used each time. In addition to this, the writer has fumigated single rooms and smaller houses with the gas. In one instance the generating jars were too small; the liquid boiled over and injured the floors and the rugs. Such an accident should be avoided by the use of large jars and by placing old rugs or a quantity of newspapers beneath the jars. THE PROPORTIONS OF INGREDIENTS Experiments and experience have shown that the potassium cyanid should be ninety-eight per cent pure in order to give satisfactory results. The purchaser should insist on the cyanid being of at least that purity, and it should be procurable at not more than forty cents per pound. The crude form of sulfuric acid may be used. It is a thickish, brown liquid and should not cost more than four or five cents a pound. If a room is made tight, one ounce of cyanid for every one hundred cubic feet of space has been shown to be sufficient. It is combined with the acid and water in the following proportions: Potassium cyanid 1 ounce Commercial sulfuric acid 1 fluid ounce Water 3 fluid ounces A SINGLE ROOM AS AN EXAMPLE