The construction of silos has been for many years one of the principal lines of investigation followed by the Agricultural Engineering Section of the Iowa Experiment Station. Its results were first published in Bulletin No. 100, which was distributed in July, 1908. This was revised and republished, owing to the unusual demand for it, in July, 1909. In addition to describing the more common types of silos then in use, this second bulletin presented a . design of a new type of silo with walls of hollow clay building blocks. In June, 1910, after the success of this silo had been carefully observed and the methods of construction developed, Bulletin No. 117 was prepared and distributed. This described in detail the construction of this type of silo and although it was published in a large edition it has been out of print for some time. This new Bulletin No. 140, covers briefly the field of both former bulletins as far as possible and adds a description of several other types of silos developed recently.

The Agricultural Engineering Section does not favor or recommend any one type of silo above all others. Different types have different merits and the cost of materials varies widely, which clearly indicates that the selection of a silo depends upon individual conditions and circumstances.