Elements of civil engineering: by Millington John

Author:Millington, John. [from old catalog]
Language: eng
Format: epub, pdf
Tags: Civil engineering
Publisher: Philadelphia, J. Dobson;
Published: 1839-03-25T05:00:00+00:00

surface becomes more disposed to rapid decay. Many varieties of brick and stone, that is, such as absorb moisture readily, and are tardy in parting with it again, ought therefore never to be selected for outside or foundation work.

66S. The same reasoning explains why external brickwork and masonry, as well as plastering, should not be done in frosty weather; for if the water necessarily introduced into the mortar should freeze before the mortar sets, it will afterwards fall to powder, and never make a strong or adhesive joint.

669. Nothing resists the effects of spontaneous decay more effectually than charcoal, and it is on this account that the bottoms of wooden posts are frequently burnt before inserting them in the ground. The error generally committed is in not burning the surface of the wood to a sufficient depth; because when advantage is to be taken of the preservative quality of charcoal, it ought to have a considerable thickness.

670. The salt of mercury, called corrosive sublimate, {bichloride of mercury,) has a wonderful power in resisting decay, as well as in preventing the occurrence of dry rot, one of the greatest enemies the builder in wood has to contend with. On this account this salt is now extensively used in ship building, and it is believed that its adoption will be attended with very beneficial consequences. Corrosive sublimate is a strong poison, and therefore requires great care and circumspection in its use. One pound of the salt is dissolved in five gallons of water, or in that proportion; and this lye or pickle being made in a brick or other close tank, the timber intended to be preserved is soaked in it until it becomes fully saturated, when it is taken out, dried in the air, and may be used.

671. The dry rot is a disease that attacks converted timber, but which seldom makes its appearance unless that timber is put in a damp situation, or is deprived of free access of air. It is therefore of common occurrence in the ends of joists or girders, that are let into walls, or in wainscotting applied against a damp wall, and is very common in ships which consist of strong ribs boarded on both sides, so as to confine air and humidity between them. Although humidity seems necessary to the production of dry rot, yet its effects and appearances are quite different from those of rotting by water. In general, it causes the surface of the wood to swell up in an appearance like blisters, with cracks between one blister and another, but without any appearance of humidity; and the wood not only looses all strength, but will crumble to a brown dust or powder on the smallest touch. The colour of the wood is always much darkened by dry rot, and it acquires a smell similar to that of mushrooms. Dry rot has the

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