Potassium occurs in various forms of combination, one of the most common being muriate of potash; another form is sulphate of potash. Kainit is another fertilizer which contains potassium, and wood ashes contain a small percentage. In all of these the potassium is generally spoken of as potash and the first two are said to contain the equivalent of 50 per cent. potash. Kainit usually contains 12 to 14 per cent. Wood ashes may contain about 3 to 6 per cent. Kainit and muriate of potash have an acid effect upon the soil, and it is wise to apply them some time before the crop is to be sown, even the fall previous, if the soil retains plant food fairly well. The commonest kind of calcium is quick-lime or lump lime. When this is “air-slaked” it becomes what is called carbonate of lime. Fifty-six pounds of lump lime contain the same amount of calcium as 100 pounds of air-slaked lime, and in using these it makes very little difference whether we apply the quick-lime or the air-slaked, provided we apply equal amounts of calcium and that the particles are equally small in both cases. In other words, 56 pounds of quick-lime or 100 pounds of air-slaked lime may be used, but both should be in as fine powdered form as possible before they are sown. Like every other fertilizer, lime is of no use until it is dissolved, and the finer it is ground before it is applied the further it may be spread and the sooner it will dissolve. It is seldom wise to apply more than from one-half ton to a ton of quick-lime per acre at any one time; and it is safer to apply this quantity every three or four years rather than larger quantities at shorter periods. Lime should be applied to the land when there is a crop upon it which can use it with advantage. A crop like clover or alfalfa, which covers the land completely, will make the best use of lime. It may injure potatoes, because it makes the land more favorable for the growth of scab, a disease which attacks potatoes. Much money can be lost by the unwise use of fertilizers, and the best way one can positively know whether it is wise to use them is to try it thus, say, with radishes, lettuce, or beans; a patch containing two or three rows may be fertilized in one way, the next one in another, others with various mixtures and, in order to determine the values of these it will be wise to leave untreated “check plats” between some of the strips. The following outline will show how to make such an experiment on about half an acre: