Spontaneous combustion does not occur very often, but it is a possibility, and it is well to bear in mind that hay may be put in the barn too green. Observation teaches that it never takes place unless the hay has been put in the barn while containing a large amount of moisture, and piled too deep. Alfalfa and other clover hays may safely be put in the barn when they contain not to exceed 30 per cent of water. If, however, they contain much more than this there is considerable danger, especially where large quantities are put together, as is the case in large, deep mows and sometimes in large stacks. A practical test which may be safely followed is to take a handful of hay, twist it as hard as possible, and if no juice can be wrung out of its stems, it is dry enough to be put in the mow. Bunches of wet hay mixed with dry hay have often caused combustion. Such should always be discarded. It is poor policy to haul clover hays into a barn after sundown, as at that time it absorbs moisture from the atmosphere very rapidly. It is a good plan for the haymaker to go into his mow every morning while the hay is curing and observe the conditions, but he should not, however, become alarmed if he finds that the top of his hay is very damp. This will always be the case, even if it was comparatively dry when put in; considerable heat develops during the night, which in turn evaporates moisture. The following morning, when the air is cool, a large percentage of this, especially if the mow is not well ventilated, is condensed and settles back on the hay. If the moisture, however, is excessive, it is a good plan to scatter a load of dry straw over the top. This will absorb the moisture in part, after which filling may be continued. In case a load has been put in the barn too wet, it should be spread to the outer edges, as there is much less danger of combustion at these places than in the center. In fact, the greatest heat is always developed in the center, where the so-called craters form, and from which moisture and gases are given off as a result of heating and oxidation below. From the fact that spontaneous combustion cannot take place until the water has all been evaporated, there is no danger until three to four weeks after the hay has been stored. During the first week or so, if the hay heats to such an extent that there is danger of combustion, it is well to open up the center as much as possible and allow some of the heat to escape. If, however, the heating has continued much longer, it is dangerous practice to open the hay at all, because all that is needed, after the water has been evaporated, is air, or oxygen to support combustion, and the mass will at once burst into flames. Sometimes combustion takes place without flames, in which case the center of the mow gradually chars, leaving the hay there as black as charcoal, and without value.