that the kyanized specimens are virtually sound in every part, while the specimens left in the natural state have become rotten and entirely worthless. The specimens shown in these plates, both kyanized and unkyanized, have been exposed to decay, with about one-half of each post buried in the ground, for upwards of twenty-eight years. Plate V. is a view of a portion of Pawtucket Street Bridge, over the Northern Canal at Lowell, built in 1849. The timber is northern white pine, and is all kyanized. No repairs were made upon it, except the surface planking, until April, 1882, when three of the stringers were found defective from dry rot, and they were replaced with new ones. Also, the lower ends of some of the braces showed signs of decay where they came in contact with the stone masonry, and the decayed parts were then cut off and replaced with new timber. repairs have been made except to the railings. now in good order, and will wear for some years yet before any extensive repairs will be needed. Since 1882 no The bridge is Plate VI. is a view of a portion of the picket fence, eight feet high, which was built around a reservoir of water on Lyndes Hill, in Lowell, in 1850. The posts are about six by eight inches, and were planted to a depth of about three and one-half feet in light, gravelly soil. The spruce timber of which the posts are made was purchased two years previous, in 1848, being a portion of a large lot originally purchased for another purpose. After seasoning the timber for two years, the posts were made into the form in which they were to be placed in the ground, and then kyanized. Six years ago, in 1885, an examination of the posts was made, when many of them were found to be more or less decayed below the surface of the ground, and a number of them were nearly rotted off at the ground surface, while a few of them were remarkably well preserved, and are so now. Occasion was then taken to strengthen the decayed posts by spiking pieces of kyanized two and one-half inch spruce plank, six and one-half feet long, to Pawtucket Street Bridge over Northern Canal, Lowell, built in 1850 of Northern White Pine, kyanized. No repairs made, except renewing surface plank, until 1882, when the lower ends of some of the braces were found so much decayed as to require renewal of that part of the lower ends which rested on the masonry. Photographed in 1891. |