This section is from the "A Complete Dictionary of Dry Goods" book, by George S. Cole. Also available from Amazon: A complete dictionary of dry goods and history of silk, cotton, linen, wool and other fibrous substances,: Including a full explanation of the modern processes ... together with various useful tables.
Sizing. Cotton is never woven in its natural state. It always receives a dressing or coating of some kind of liquid size which is allowed to dry before the operation of weaving begins. The size usually consists of a preparation of wheat flour made into a thin paste. The early cotton weavers of this country found that the threads soon became injured and frayed by contact with the machinery; and the warps frail even at first, became so fragile by rubbing against reeds and shuttles that breakages became so frequent as to cause serious loss of time, through stopping the loom to pick up and join anew the broken ends. This difficulty was in some measure remedied by rubbing the yarn with a mixture of paste and grease, the weaver leaving off now and again to dress a fresh length of yarn. After the establishment of the power-loom the inconvenience and loss were still felt, even to a greater degree, and several attempts were made to meet the difficulty, but without effect, until a dressing machine for preparing the whole length of warp before weaving was produced. The object of this machine is to apply the size in such quantity that it will diminish the roughness on the fibrous surface of the warp, and increase its strength, thereby facilitating the weaving. The yarns from several rollers are unwound and made to pass through the size and then between rollers which squeeze the glutinous composition into the very heart of the thread. Thence the yarn passes over drying cylinders, made of sheet iron and copper, heated within by steam. This quickly dries the size, and prepares the yarn to be wound upon the weaver's beam, a roller which receives uniform layers of warp from end to end.