Each bid shall be accompanied by a certified check, or cash, to the amount of ten (10) per cent of the total amount of said bid figured on the quantities given herewith, the lowest alternative total being allowed. Said amounts deposited with bids, shall be held until all of the bids have been canvassed and the contract awarded and signed. The return of said check or cash to the bidder to whom the contract for said work is awarded will be conditioned upon his appearing and executing a contract for the work so awarded and giving bond satisfactory to said Board of Trustees, for the fulfillment of each contract in the amount of fifty (50) per cent of the amount of each contract. The said Board of Trustees reserves the right to reject any or all bids. Accompanying the contract form are plans which, together with the specifications, show the work on which said tenders are to be made. The proposal must not be detached herefrom or from the contract by any bidder when submitting a bid. =112. Proposal.=—The proposal is a blank printed form on which the bidder is required to enter the prices for which he proposes to do the work. The proposal blank is necessary in order that the bids may be sufficiently uniform for proper comparison. Sewers are often paid for, particularly for small sizes, per foot of completed sewer as measured along the center line of the pipe parallel to the surface of the ground with the exterior length of manholes and other structures deducted. Sometimes, under other conditions, a different rate is allowed for each additional two feet of depth of sewer, and special structures, such as manholes, catch-basins, flush-tanks, etc., are paid for at a unit price according to the depth. Water connections to flush-tanks are paid for per foot of length of service pipe laid. In especially large or difficult work, materials are paid for at a unit-price, for example, per cubic yard of excavation, per cubic yard of concrete, per thousand feet board measure of lumber, etc. The following example is taken from the contract for the North Shore Intercepting Sewer previously quoted, to indicate the type of Proposal used: PROPOSAL FOR THE CONSTRUCTION OF THE NORTH SHORE INTERCEPTING SEWER To the Honorable, the President and the Board of Trustees of the Sanitary District of Chicago: Gentlemen:__The undersigned hereby certi____ that ____ ha____ examined the specifications and form of contract and the accompanying plans for the construction of the North Shore Intercepting sewer, and ha____ also examined the premises at and adjacent to the sites of the proposed work, as herein described, and the means of approach to the said sites.