"Treated pine blocks shall weigh as much as water. Treated gum blocks shall weigh as least 59 lbs. per cubic foot and any other wood at least 20 lbs. per cubic foot more than the recognized weight of such untreated blocks.
"Blocks cut from the several classes of timber allowed under these specifications will require different manipulation and treatment, and for this reason the exact methods of applying the mixture to the several timbers named will not be specified, it being understood that whatever method is used the process must conform in every respect to the best and most advanced knowl edge of the art, the purpose of the city being to allow the contractors to manufacture specification blocks by following any preferred detail and by the use of any particular plan or machinery which may be properly adapted to secure the results herein required.
"The creosote oil is to conform to the following specifications when tested, as follows: " The gravity at 68° F. shall be not less than 1.12. When distilled in a retort with a thermometer sus pended not less than one inch above the oil, it shall lose not more than thirty-five (35) per cent up to 315 degrees Centigrade, and not more than fifty (50) per cent up to 370 degrees Centigrade. The oil is to be free from adulteration; it must not be mixed with or contain any foreign material.
"The resin is to be solid resin obtained from pine. It is to be reduced to a fine dust by grinding and then incorporated with the hot creosote oil in a suitable mixing tank until the proper proportions are secured." The specifications employed in St. Louis in 1908 are as follows: "After the blocks have been inspected and found satisfactory they shall be placed in an air tight chamber where by means of superheated steam and the use of a vacuum pump, all sap in the blocks shall be vaporized and the moisture in them removed. When the blocks are thoroughly dry, and while the cylinder is under vacuum of fifteen to twenty inches of mercury, heavy creosote oil, of the grades known as Kreodone, or Republic Creosote Paving Oil, especially prepared for paving purposes, shall be admitted to the cylinder and pressure added until the pressure in the cylinder shall be at least sixty pounds to the square inch. The blocks shall remain in the cylinder until they have absorbed twelve pounds of oil per cubic foot of timber and until the creosote oil shall have impregnated the timber through the entire thickness of the block, and to the satisfaction of the Board of Public Improve ments and the Street Commissioner."