The Bulletin Of The Airplane Engineering Department PDF Download

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1918 edition. Excerpt: ...constituents by the hot water. More raw material is added from time to time, until a sample of the liquid shows it to be of the right strength. When the desired density is obtained the liquor is clarified in the same way as described for bone glue. Flnal Treatment of Bone and Hide Glues Concentration, drying and bleaching are the final steps in the manufacture of glue by any of the above methods. The liquor, after being obtained by any of these processes, is concentrated in a vacuum pan heated by steam. Solutions of glue are very susceptible to change by prolonged boiling at atmospheric pressure, and if the glue liquors were evaporated in an open vessel at 100 G. (212 F.), the product would be of inferior quality and dark in color. For this reason it is necessary to evaporate the liquors at a lower temperature than the boiling point of water, which is achieved by lowering the pressure. Multiple evaporators are employed in which the steam from one pan is used to heat the next, and so on. The concentrated gelatin liquor is allowed to cool, and when it sets to a jelly is cut into sheets of any desired thickness. The processes of cooling and drying the glue require great care. Frequently whole batches will be spoiled, due to causes which are not always clearly understood. The liquor must be cooled quickly, as the liquefying bacteria will rapidly injure the glue if the cooling process is prolonged. Refrigerating machines are therefore used, so as to obtain a temperature of about 0 G. This is about the lowest temperature it is safe to use, as below this point the jelly becomes too hard and difficult to cut. After being cut into_ sheets, the solidified jelly is dried by spreading the sheets on metallic netting, preferably of galvanized iron...