General. - Each proposal must be accompanied by a letter from one or more wood block manufacturers, each letter giving the location and capacity of his plant or plants and stating that.the said manufacturer is familiar with and understands these specifications, and that he is ready and willing to furnish to the bidder if the contract be awarded to same, wood blocks manufactured in strict accordance with these specifications and in sufficient quantity to complete the improvement within the required time.

After the opening of bids, the successful bidder, if bo requested by the Engineer, shall within five (5) days after such request, furnish for testing samples of all materials desired. Should the material which the Contractor proposes to use be found for any reason unsatisfactory, then the Contractor must supply other material which will be acceptable. Failure to do so will be deemed cause for rejection of his bid and forfeiture of bidding bond or deposit.

The successful bidder must also within five days from opening of bids send a letter to the Engineer stating the plant from which he proposes obtaining the blocks, and which of the three below mentioned methods of separation he proposes to use. No change in the above will be permitted without the written permission of the Engineer.

Timber. - The wood to be treated shall be Southern yellow pine, Norway pine or Tamarack, only one kind of wood, however, to be used in any one contract. The blocks must be cut from what is known as prime timber, namely: All timber must be sound, well manufactured, sawbutted, all square edge, and shall be free from the following defects: unsound, loose and hollow knots, worm holes and knot holes, through shakes and round shakes that show on the surface.

The number of annual rings in the one inch which begins two inches from the pith of the block shall not be less than six, measured radially, provided, however, that blocks containing between five and six rings in this inch shall be accepted if they contain 33 1/3 per cent. or more summer wood. In case the block does not contain the pith, the one inch to be used shall begin one inch away from the ring which is nearest to the heart of the block. The blocks in each charge shall contain an average of at least 70 per cent. of heartwood. No one block shall be accepted that contains less than 50 per cent. of heartwood.

Size of Blocks. - The blocks shall be six to ten inches long, but shall average eight inches; they shall be three and one-half inches in depth and three inches in width. A variation of one-sixteenth of an inch shall be allowed in the depth, and one-eighth of an inch in the width of the blocks from that specified.

In case blocks with integral lugs are used, the specified width shall be interpreted to be to the outside edge of the lugs, and in such case the allowable variation in width shall be only one-sixteenth of an inch.

The blocks used may be the ordinary rectangular blocks of the above dimensions, or they may be blocks with special provisions for spacing. Under head of Special Requirements will be specified the kind of blocks to be used. If blocks with special provisions for spacing are required, the following shall be observed.

Provision for Spacing. - The blocks shall be provided with satisfactory means of separation, so that, when laid, they shall be firmly held apart all around a distance of not less than three-sixteenths (3/16) inch nor more than one-quarter (1/4) inch. This separation may be obtained by any one of the three following methods:

1st - There shall be driven four (4) nails on one side and two (2) nails on one end of each block. The nails shall penetrate the blocks approximately three-quarters (3/4) inch and shall project uniformly one-quarter (1/4) inch. To insure the uniformity of this projection the nails must be double headed or conical headed with exactly one-quarter (1/4) inch from the base to the outside of head. The diameter of the base against the wood shall be approximately one-quarter (1/4) inch. The nails in end of the block shall be in the vertical center line and three-quarters (3/4) inch from top and bottom. The nails in the side shall be in pairs one (1) inch from ends and three-quarters (3/4) inch from top and bottom.

2nd - Each block shall have two vertical lugs on one side and one vertical lug on one end. The lugs shall be V-shaped, shall extend the full length of the block and shall be an integral part of the wood. The lugs shall project three-sixteenths (3/16) inch from the body of the block and shall be approximately one-quarter (1/4) inch wide at the base. The end lug shall be in the center line of the block and the side lugs shall be spaced five (5) inches apart equally distant from the center line.

3rd - Three creosoted strips or spacers may be nailed to each block. These strips shall be of same cross-section and length as the lugs above described, and shall be fastened to the blocks in the same position. Each strip shall have two small wire nails penetrating three-quarters (3/4) inch into body of block.

Preservative. - The preservative to be used may be either a coal-tar distillate oil "A" or a coal-tar paving oil "B" as herein specified.

Oil "A" Coal-Tar Distillate. - The oil shall be a distillate of coal gas tar or coke oven tar, and shall comply with the folowing requirements:

1. It shall not contain more than 3% of water.

2. It shall not contain more than 0.5% of matter insoluble in benzol.

3. The specific gravity of the oil at 38 degrees C. shall not be less than 1.06.

4. The distillates based on water-free oil shall be within the following limits: Up to 210 degrees C, not more than 5%.

Up to 235 degrees C, not more than 15%.

The residue above 355 degrees C, if it exceeds 10%, shall have a float test of not more than 50 seconds at 70 degrees C.

5. The specific gravity of the fraction between 235 degrees C. and 315 degrees C. shall not be less than 1.02 at 38°/13.5° C.