In the first place, if land is unusually sour, you can determine this fact by a simple test. Buy a pennyworth of blue litmus paper from a drug store. Mix some of the suspected soil with a little water and bury the litmus paper in the mixture. If the paper turns red the soil is sour. In the second place, the leguminous crops are fond of lime. Clover and vetch remove so much lime from the soil that they are often called lime plants. If clover and vetch refuse to grow on land on which they formerly flourished, it is generally, though not always, a sign that the land needs lime. In the third place, when water grasses and certain weeds spring up on land, that land is usually acid, and lime will be helpful. Moreover, fields adjoining land on which cranberries, raspberries, blackberries, or gallberries are growing wild, may always be suspected of more or less sourness. Four forms of lime are used on land. These, each called by different names, are as follows: First, quicklime, which is also called burnt lime, caustic lime, builders' lime, rock lime, and unslaked lime. Second, air-slaked lime, which is also known as carbonate of lime, agricultural lime, marl, and limestone. Third, water-slaked, or hydrated, lime. Fourth, land plaster, or gypsum. This form of lime is known to the chemists as sulphate of lime. Do not forget that this last form is never to be used on sour lands. We shall therefore not consider it further. Air-slaked lime is simply quicklime which has taken from the air a gas called carbon dioxide. This is the same gas that you breathe out from your lungs. Water-slaked lime is quicklime to which water has been added. In other words, both of these are merely weakened forms of quicklime. One hundred pounds of quicklime is equal in richness to 132 pounds of water-slaked lime and to 178 pounds of air-slaked lime. These figures should be remembered by a farmer when he is buying lime. If he can buy a fair grade of quicklime delivered at his railway station for $5.00 a ton, he cannot afford to pay more than $3.75 a ton for water-slaked lime, nor more than $2.75 for air-slaked lime of equal grade. Quicklime should always be slaked before it is applied to the soil. As a rule lime should be spread broadcast and then harrowed or disked thoroughly into the soil. This is best done after the ground has been plowed. For pastures or meadows air-slaked lime is used as a top-dressing. When air-slaked lime is used it may be spread broadcast in the spring; the other forms should be applied in the fall or in the early winter. SECTION LXVII. BIRDS What do birds do in the world? is an important question for us to think about. First, we must gain by observation and by personal acquaintance with the living birds a knowledge of their work and their way of doing it. In getting this knowledge, let us also consider what we can do for our birds to render their work as complete and effective as possible.