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    POLYPROPYLENE
    November 12, 1999 - Bartlesville, Oklahoma, U.S.A.

    In Bartlesville, Oklahoma, a plaque was placed on the site of the laboratory where the polymer polypropylene was invented, designating it a National Historic Chemical Landmark by the American Chemical Society. The first commercially successful use of the new material was in the Hula Hoop®. In 1951, J. Paul Hogan and Robert L. Banks, research chemists working for Phillips Petroleum Company, discovered the polymer unexpectedly during experiments with catalysts while trying to convert the natural gas components ethylene and propylene into compounds useful for gasoline. Later, they also developed a new catalytic process for making high-density polyethylene. Phillips soon invested in new plastic manufacturing plants.

    PITOT TUBE
    November 12, 1732 - Academy of Sciences, Paris

    Henri Pitot read a paper to the Royal Academy of Sciences in Paris about an instrument he had invented to measure the flow velocity at different depths of water in the River Seine. It had a scale and two open vertical glass tubes on a wood frame. The lower end of one pointed down, the other bent at 90 facing the flow. The belief of the time was that flow velocity at a given depth was proportional to the mass above it, meaning increasing velocity at greater depth. Recording the difference in liquid levels in the two tubes, he showed the opposite was true. Henri Darcy improved the design, with the support of Henri Bazin. Today, the Pitot tube has an important application in aerodynamics for the measurement of the airspeed of aircraft.

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Evaluating A Roof Repair :

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Evaluating A Roofing Replacement:

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Having the opportunity to estimate the amount that it may cost to replace a roof is often a fragile calculation. For a roofing contractor, they often keep in mind various factors directly to ensure about whether or not a straightforward repair needs to be done, or total replacement.

Usually, a roof should last more than two decades. The longevity of the roof is usually dependent on how well it was actually maintained over the years. Climatic conditions can also be a factor.

For example, water can get underneath shingles after which become ice. This may cause leaks, plus a considerable amount of damage. When the sun is especially intense, it can cause shingles to blister.

If your roof does find yourself needing to be replaced, step one will be to have a contractor measure your entire home. They'll measure the time no matter what the roofing system by its height up to the peak. They'll determine the length of time the whole system's ridges are, and decide how much of the cover needs to be replaced.

The entire roofing structure is calculated in squares which equals 100 ft² or 10 feet times 10 feet. For instance, a 1400 ft roof would contain 14 roofing squares. While these square help contractors to figure out their pricing estimate, other reasons, like costs of tearing off the present roof, should also be calculated.

Determining the number of squares on any roof aids the homeowner after they try to figure out what their most suitable choice is in relation to replacements. However, its not all roof is strong enough to accommodate all kinds of roofing material. The weight of an asphalt shingle is considerably less when compared to a concrete tile, and to discover the roofing system may not be devised to handle the extra weight.

The total price in estimating the price of a roof replacement is usually highly depending on the amount that the roofing contractors charge per square. That is why you will need to receive at least 3 - 4 bids from reputable contractors in the community. Further, they'll have the opportunity to try your roof, discover your material preferences, and come up with a reasonable estimate of the volume of a brand new roof shall be cost.

Understand that its not all factors of a roofing replacement can be found up front. For instance, there could be a damage besides the substrate, or a pest problem. However, based upon just how much a contractor charges per square in addition to materials chosen, the homeowner can certainly estimate how much it may cost to swap out the roof.

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