TESTS FOR WOOD BLOCKS.
Specification requirements for wood blocks vary widely in different places throughout the country and no systematic method has been adopted for the inspection and testing of the blocks. A number of tests have been proposed for use both at the plant where the blocks are treated and after the blocks have been delivered at the site of the pavement. Inspec tion of the blocks is frequently made before treatment, as well as tests of the oil to be used in the treatment, an inspector being kept at the plant for the purpose while the blocks are being prepared. The thoroughness of the treatment is determined by the difference in weight of treated and untreated blocks.
For the examination of wood blocks after their delivery at the point of use, several tests are in use or have been proposed: a. The blocks are inspected as to their size, shape, and freedom from defects.
b. Blocks may be split and examined as to the thoroughness of the treatment, and a weight test applied to determine whether a sufficient quantity of oil has been absorbed by the block.
c. Tests of absorption are made by first drying the blocks and then soaking them in water, thus deter mining the amount of water that may be absorbed.
d. The character of the oil with which the block has been treated is tested by extracting the oil with carbon bisulphide and then subjecting it to tests to determine whether it conforms to the specifications for oil to be used in the treatment. The separation of the creosote oil from the solution is effected by. distillation, the sol vent being first removed at a temperature of about 120 degrees Centigrade and the creosote oil below about 370 degrees Centigrade.
e. It has been proposed * to test the resistance to abrasion of the blocks by grinding them upon a disk machine, but no records are available as to results obtained in such tests.
The following extracts show the tests imposed by Mr. Tillson in specifications for work in New York
City in 1908: " After treatment the blocks are to show such waterproof qualities that after being dried in an oven at a temperature of 100 degrees for a period of twenty four hours, weighed and then immersed in clear water for a period of twenty-four hours and weighed, the gain in weight is not to be greater than three and one-half (31) per cent.
"Fine turnings from the block shall be placed in a suitable extraction apparatus and the oil completely extracted therefrom with ether or carbon bisulphide. The oil so extracted shall be placed in a suitable still and distilled. The portion up to 120 degrees Centi grade, consisting of the solvent, is to be collected apart. The oil shall then be distilled up td 370 degrees Centi grade. The creosote oil thus obtained must conform in all respects to the requirements of paragraph 39 (see p. 269).
"The Engineer shall have tests and examinations made at the contractors' works of the materials and blocks proposed to be used, and reject any or all of such materials and blocks as he may consider not to be in compliance with these specifications. The Borough President shall appoint an inspector at the expense of the contractor, who shall inspect the lumber and other materials used in the manufacture of the blocks, and the treatment of the blocks; and he shall reject any of such materials and blocks as he may consider not to be in compliance with these specifications.
"The blocks shall be carefully inspected after they are brought on the line of work, and all blocks which in quality and dimensions do not conform strictly to the requirements will be rejected and must be imme diately removed from the line of work."