CHUNAM.
Chunna; Chunnam, HIND. I Sunamu; Choonnoo, TEL. Chunambu,. . . TAIL I Chuna or Chun= is a term applied to quick lime made from nodular limestone, from lime stone rock, from marble, or from calcined shells; also applied to plaster and mortar. The chunam plaster of Madras, long famed for its marble-like polish, is prepared either from shells or lime stone. The shells generally used at Madras are both recent and fossil, but the latter, of recent species, aro found in extensive beds a few feet below the surface, on the banks of the Pulicat lake and other low marshy placo on the sea coast, which are covered by the sea at high water.
The shells are calcined with charcoal, one parali of charcoal being allowed to every two parahs of chunam. The kilns generally used are calculated to hold altogether 60 parabs, that is, 40 of shells and 20 of charcoal. A small arch, 1 foot 3 inches in height, the saine in breadth, and raised 5 feet above the surface of the ground, runs longitudi nally through the kiln ; the top of this arch is a grating of brick on edge, which is partially covered with broken tiles, so that neither the shells nor charcoal can drop through them, but small apertures are left for the escape of the ashes .and for the necessary circulation of air. Over this bed a layer of charcoal is first placed throughout, about 3 inches in thickness, and fire applied. When sufficiently kindled, the mixed shells and charcoal are laid in small heaps of not more than k of a parah each at about 1 foot 6 inches apart, and when the fire bas been com municated to them, the intermediate spaces must be filled up with more shells and charcoal to a level; and when the fire has thoroughly extended to them also, another row is to be laid in a heap upon, this mass, 3,9 was done in the first instance ; and in the subsequent operations are to be repeated in the same manner until the kiln is filled. The transverse arches are to promote the requisite current of air, and the windward ones are invari ably to be kept open, whilst those on the opposite side must be closed. The kilns used at Madras are built of brick or clay, and require renewal every three years. The shells will be sufficiently calcined in 12 hours, and 24 more are required to cool them, so as to admit of their being moved and the charcoal sifted from them. It is found that chunana thus- prepared and slaked to a powder is increased to double its original bulk when in the form of shells.
For plastering with chunam at Madras, if for one coat, the plaster is composed of one part of chunam and one and a half of river sand, thoroughly mixed and well beaten up with water. This operation is usually performed by women, who stand round a small stone trough prepared for the purpose, into which the ingredients are thrown and gradually moistened with water, as the process of mixing proceeds. The women use wooden pestles shod like a rice-pounder. The plaster, when mixed, is taken out of the troughs and made int,o conical heaps, where it remains till required, and may be kept without injury for several months ; but when left, for any time, a small cistern or hollow is made at the top of the heap, into which water is oce,asionally poured. Before applying the plaster, the wall is trimmed with a trowel and swept per fectly clean, and then slightly sprinkled with water. The wall being ready, the plaater is put into small wooden boxes at convenient places among the bricklayers, by whom it is mixed up with jagari water, lb. of jagari or coarse sugar being allowed to every parah of quicklitue, until it is brought to the required consistency ; it is then laid on with a trowel above half an inch thick. and levelled with a flat wooden rule, being afteswards smoothed with a wooden rubber till it acquires an even surface. During the process of rubbing, the plaster is occasionally sprinkled with a little pure white lime mixed with water, to give it a hard surface. If for two coats of chunarn, the, first coat is applied as already described, with the exception that the surface is left rough, and no pure lime is applied during the process of rubbing. A day or two after the first coat is applied, and while moist, the second is laid on. The plaster used for the second coat consists of three parts of litne and one of white sand. These are mixed as before, and afterwards ground by women on a flat stone with a small stone roller, till they are reduced to a fine paste. This is laid on a wooden rubber, and applied with care over the first coat about of an inch thick. It is then rubbed down perfectly smooth with a small trowel, and afterwards polished with a crystal or smooth stone rubber, and as soon as it has acquired a fine polish, a little very fine potstone (Ballapum) powder is sprinkled on it to increase the white ness and polish, and the polishing continued. The second coat ought to be applied and finished in one day, for it usually hardens too much during the night to be polished the following day, except in damp weather. The practice is to continue polishing the plaster until it is quite dry, and a number of bricklayers are employed, in order that it may be well polished the first day. Moisture continues to exude from the plaster for some days after it is completed ; this must be carefully wiped off with a soft cloth, and the wall kept perfectly dry till the moisture entirely ceases. For three coats of chunam, the first coat is as above, but it is left a fortnight or three weeks to dry before the second coat is applied. The plaster for the second coat consists of one part of lime and one of fine river sand, freed from the coarser particles and clay by sifting. It is well mixed and beaten up in a clean trough, and applied over the first coat about of an inch in thickness, the first being previously inoistened with a little water. It is next rubbed down in the same manner as the first coat, but acquires a much smoother surface, the plaster being of a finer quality. A day or two
afterwards, when it has had tinie to dry, the third coat is applied. It consists of four parts of lime and one of fine white sand. These, after being well mixed, are reduced by grinding to a very fine paste, quite free from grittiness. This is put into a large earthen jar, of the size nearly of half a hogshead, aud mixed with the white of eggs, sour milk (tyre), and ghi, in the proportion of 12 eggs, measures of tyre, and lb. of ghi to every parah of plaster. These are all thoroughly mixed, and rubbed between the bands till the ingredients are thoroughly incorporated, and the composition reduced to a uniform consistent paste a little thicker thau cream, and perfectly free from grittiness. The plaster is now fit for use, and is put on with a wooden rubber about of an inch thick, and gently rubbed till it becomes perfectly smooth. Immediately after this, another coat of still finer plaster is applied, consisting of pure lime ground to a very fine powder, and after wards mixed with water in a clean tub, till it is of the consistency of cream. This is put on about Ile of an ine,h thick with a brush, and rubbed gently with a small trowel till it acquires a slight degree of hardness. It is then rubbed with a rock-crystal or stone rubber till a beautiful polish is produced, not forgetting to sprinkle the wall with fine potstone (Ballapum) powder during the process of polishing. If the plaster is not entirely dry on the second morning, the operation of polishing ought. to be continued until it is quite dry. The moisture, as above directed, must be carefully wiped off, and the wall kept quite dry till all appearance of moisture cease. The result of the process depends chiefly on the plaster for the upper coat being reduced to a very fine Taste perfectly free from grittiness, and on its being, after it is applied to the wall, rubbed con stantly with great care till it is quite dry and has acquired a very fine polish. The Ivan ought then ,to be frequently wiped with a fine clean cloth to remove the moisture, and it may be occasionally (hutted with Ballapum powder. The stone used in polishing it is rock-crystal or a white quartz pebble about 3 inches long aud 11 broad, the face of which has a very fine polish. The wall is rubbed -with this for one or two days, the tuoisture being carefully wiped off every morning, and potstone (Ballapum) powder sprinkled on it several times iluring the day. When the lime is prepared from sea!shells, these are first cleaned and washed, and then calcined with charcoal, care being taken to exclude everythiug likely to injttre the whiteness of the lime ; very white sand only is employed, as common sand destroys the brilliancy of the plaster. When white sand, is not procurable, white rock- crystal or quartz pebbles reduced to a fine powder may be substituted. Mortar for building consists of one part of dun= and two of sand. Imme diately before being used, the mortar is mixed with ja,gari water, 1 lb. of jagari being allowed to every parah of lime. It is used in a much more fluid state than is the practice in Europe. When shell-lime is used in situations requiring a hydraulic content, it should be mixed with burnt clay in Fowder ; fresh burnt tiles more or less broken are in general conveniently procured. In building the pier at Masulipatam, Captain Buckle employed a cement consisting of one part of lime, one of the tile dust, and two of sharp river sand, and it appeared to answer well. Jagari was used in the usual proportion of one pound to a parah of chunam. Limestone abounds in most districts of Southern Asia, but the qualities of the different varieties are best ,aseertained by experiment. When found in large blocks of very compact stone, the breaching of it forms a consider able item in the expense. Such stone as yields very hydraulic lime is not suited to the purposes of ordinary building, unless the precaution is taken of keeping the work constantly wet. The best form of kiln for burning stone with charcoal is given by Captain Smith in his translation of Vicat, plate 1, fig. 11 and 12. When wood is used, the spheroidal form of kiln is recommended. It will be found to facilitate the expulsion of carbon, if the stone is well moistened in water previous to placing it in the kiln. It should be remarked that nothing but clean sand should be added to the hydraulic limes; such limes should be used immediately after slaking. 1Vhen used in situations requiring hydraulic cement, no raore water should be used iu slaking it than is sufficient to reduce it to a fine dry powder. Magnesian limes have been found at Salem and in the Tanjore district, where it Walt used with suc cess by,Captain Cotton in forming the anicuta ; the cement formed with it was stronger than that formed with other lime. It should not be im mersed immediately on being used. Much con troversy has ocCurred in regard to the advisability of using the lime while hot ; the generally re ceived opinion is that it should be so nsed ; but in' regard to the pare limes, free from clay and iron, that is, without hydraulic properties, Ulla course is questionable. It was not permitted in Rome ; and lime mortar kept moist has been found suitable for building after the lapse of several hundred years ; lime used hot is seldom thoroughly slaked. A common practice in India is to mix the slaked lime and sand, form it into heaps, on the summit of which is formed a hollow, which is kept constantly filled with water. Shell-linte, so kept and subjected to the usual beating when used, seemed to Mr. Rohde at least as good as when at first burned; hydraulic limes, including of course all which become hard under water, ought no doubt to be used hot. At Ternate, and other coral islands, coral is largely burned into nine for mortar.—lialtde, 111,58,