Dr. Buchanan, in his Journey front Madras through the countries of Mysore, &c. gives a description of the Saymbrumbacum tank near Madras, which ap pears to us well deserving of the attention of persons interested in the construc tion of water-works, as there are probably situations in this country where similar advantages might be taken of the natural configuration of the hilly districts. The Saymbrumbacum tank has not been formed by digging, like those in Bengal, but by shutting up, with an artificial bank, an opening between two natural ridges of ground. The sheet is said to be seven or eight miles in length, and three in width, and in the dry season is let out in small streams, as wanted, for Irrigation. In the rainy season it receives a supply of water from the river Chir nadi, and from several small streams that are collected by a canal. It is provided, in different places, with sluices or weirs, of stone, which are from 20 to 30 feet wide, and some feetjower than the other parts. On the surface they are strongly fortified by large stones, placed in a sloping direction, so that the water rushes over with out undermining the bank, and is conveyed away from the fields by a canal. This is a matter of the utmost importance, as there are instances where, the banks of these large tanks having given way, whole villages have been destroyed ye the torrent. In order, however, that when there is plenty of rain the tank may be completely filled, a row of stone pillars is placed on the top of the sluices (weirs); and on the water rising to a level with their base, a temporary wall is formed of mud, sticks, and straw, placed between the pillars so as to con fine the water till it rises as high as the top of the bank. People watch this night and day, in order to break down the temporary bank should any additional rain endanger the whole. The water is let out to supply the fields, by a sluice lined with cut stone or bricks, formed through the bank, on a level with the country. The inner end of this sluice is covered by a fiat stone, in which is cut a conical opening, that can be shut or opened by a conical plug or valve, fixed to a bamboo staff, and which is secured in its place by passing through holes made in cross guiding-bars, let into two pillars of stone, which rise above the level of the water in the tank. This tank is said to be sufficient to supply with water the lands of thirty-two villages, for eighteen months, should the rains fail ; such a reservoir is therefore of inestimable value.
WAX. An oily concrete matter, usually considered to be gathered by bees from plants; though Huber, who was a close observer of nature, and the habits of bees in particular, asserts that wax is an artificial production, made by the bees from the honey they collect; that they cannot procure it, unless they have honey or sugar for the purpose ; and that raw sugar affords more than honey. Wax was long considered to be a resin, from some properties which it possesses in common with resins. Macquer found that wax resembles resin only in being an oil, rendered concrete by an acid ; but that it differs essentially from these in the kind of the oil, which, in resins, is of the nature of essential oils, while in wax, and other analogous oily concretions, (as butter of cocoa, butter of milk, fat of animals, spermaceti, myrtle wax,) it is of the nature of mild unctuous oils, that are not aromatic, and not volatile, and are obtained from vegetables, by expression. Dr. Ure considers it probable, that the acidifying principle, or oxygen, and not an actual acid, may be the leading cause of the solidity, or low fusibility of wax ; but it has been observed, that by digesting the nitric or muriatic acid upon fixed oils, the oils pass into a state resembling wax. The natural colour of wax is yellow, and it is whitened by exposure, in thin laminae, to the air and sun. Alkalies dissolve wax, and render it miscible in water. In
China and North America, wax is procured directly from plants, and is then called vegetable-wax. In order to obtain bees, wax in a pure state, what remains of the combs, after separating the honey, is put into a copper, with a quantity of water, which is made to boil over a slow fire, and stirred frequently with a stick. When the wax has been thus thoroughly melted, it is strained through canvas bags, and the residue in the bags is forced out by a press, whilst hot, and received into a vessel of water. When all the wax has been thus cleared of the r impurities, it is again melted over water, and the scum which arises in grosser is carefully skimmed off; after which, it is poured into pane or moulds of the size required, to solidify. Wax keeps better in large cakes than small ones : any sediment that may remain at the bottom of the cakes is scraped off before bleaching.
The ordinary process of bleaching wax, consists in first melting it at a low heat, in a cauldron, from whence it is allowed to run out by a pipe at the bottom, into a capacious vessel filled with cold water, in which is fitted a large wooden cylinder, that is made to turn round continually on its axis, upon which the melted wax falls. The surface of the cylinder being constantly wet, the wax does not adhere to it, but lays solid and flat, acquiring the form of ribbands. The continual rotation of the cylinder carries off these ribbands as fast as they are formed, and distributes them through the tub. The wax is then put upon large frames covered with linen cloth, which are supported about eighteen inches above the ground, in situations exposed to the air, dew, and the sun. The thick ness of the several ribbands, thus placed upon the frames, ought not to exceed an inch and a half, and they ought to be removed from time to time, in order that they may all be equally exposed to the action of the air. If the weather be favourable, the colour will be changed in a few days. It is then to be re-melted, formed into ribbands, and exposed to the air as hefore. These opera tions are to be repeated, until the wax is rendered perfectly white ; after which it is to be melted into cakes, or formed into candles.
Of late years, the sulphuric acid, and other chemical agents, have been pro posed for shortening the process of bleaching wax, but we are inclined to believe i that they have not been successfully carried into practice, as the manufacturers, we are informed, adhere to the old process above described. To what extent chlorine has been applied to this purpose, or in what manner, we are Jot in formed ; but the process employed by Mr. Davidson, of Glasgow, and recently patented by him, is stated, in the specification, to be as follows :— " The wax or tallow is heated to about the temperature of boiling water, in an iron vessel lined with lead, when the oxymuriate of lime, (chloride of lime,) or the oxymuriate of magnesia, (chloride of magnesia,) is to be added, either in solution with water, or in the dry state, and then intimately mixed and well stirred up with a wooden spatula. When these materials have acted upon each other a sufficient length of time to discharge the colour from the wax or tallow, the lime or magnesia is to be removed, by adding dilute sulphuric acid, or some other acid possessing a greater affinity for those earths than chlorine. The whole is then to be boiled, until the earth employed is separated." For the bleaching of wax, the solution of the chloride is to be in the propor tion of from 14 to 28 pounds of the salt, to 112 pounds of water; and an equal quantity by weight, of the solution and of the wax, to be employed in the pro cess. The sulphuric acid should be of the specific gravity 1.8485, and be diluted with from twenty to thirty times its weight of water.