[5] Messrs. Vauquelin and D’Arcet state that they have seen in soap-works the soldering of vats lined with lead crumble in a few days to a powder. The same has been remarked of leaden pipes passing through certain soils. [6] The solder often sticks without uniting and the workman may be quite ignorant of his imperfect work; and thus gas, water, or dangerous liquids, may be allowed to escape. CHAPTER IX. THE INTERIOR--PLASTERING AND PAPER-HANGING. As men rise above the rude condition of uncivilized nations, they are not satisfied with the mere _necessaries_ of life. Their standard of comfort becomes elevated. Those things which are luxuries to the lowest class are comforts to the next higher class, and necessaries to the class which is higher still in the social scale; so that the interpretation given to the words, “luxuries,” “comforts,” and “necessaries,” becomes a sort of index whereby to mark the grade which an individual occupies. A roof to cover the dwelling, a glass window which may exclude the wind and the rain, while it admits light,--a fire-place, with appliances for carrying off smoke and the products of combustion--however far above the standard of the uncivilized man--are not sufficient for the Englishman of middle station. He must have his rooms nicely squared and neatly fitted; the roof must be concealed from view by a smooth white ceiling; the rough brick walls must be covered not only with plaster, but with an ornamental covering of paper or paint. Hence arises occupation for many artisans whose sole business is to make the dwelling agreeable to the eye, after the more necessary and indispensable parts of the structure have been finished. Plastering Walls and Ceilings. The occupation of the plasterer is generally united with that of the bricklayer. The business of the plasterer, as such, is to cover over the rough walls and ceilings of a building with _plaster_, which is the name given to a better kind of mortar, made of lime only. When this plaster is of the coarser kind for the under or first coating, cow-hair is mixed with it to make it bind better. When a plain brick wall is to be plastered, the surface is at once covered with the plaster, this adhering readily to the rough brick-work: but for ceilings or partitions, a groundwork of laths is required to receive the first coating. Laths are of different sizes and qualities, according to the various work for which they are intended. Those used by the plasterer are termed _single_, and are about from two to three feet long, an inch broad, and a quarter of an inch thick. They are split out of a coarse kind of deal. _Double_ laths are considerably longer and thicker, and are sawn out: they are therefore regular in their size. They are used for better work in plastering, but chiefly by tilers or slaters.