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 the 17th century, and received municipal institutions in 1779; but within a very few years it became a wealthy town, owing to its situation in a very fertile district. Since it was brought into railway communication with Ryazhsk (81 m. west on the railway between Moscow and Ryazan) it has become the chief centre for the trade in wheat raised in the governments of Tambov, Penza, Saratov and in the eastern districts of the government of Ryazan. There are also extensive dealings in flour, hemp-seed, tallow and potash.

MORTAGNE, a town of northern France, capital of an arrondissement in the department of Orne, 24 m. E.N.E. of Alençon by rail. Pop. (1906), 3383. A vaulted entrance (15th century), relic of an old stronghold, and the church of Notre-Dame (15th and 16th centuries) with a fine northern portal are of interest. The town is the seat of a sub-prefecture and of a tribunal of first instance, and is a celebrated market for horses of the Perche breed. Mortagne, once capital of the Perche, dates from the 10th century.

MORTAIN, a small town in the department of La Manche, France, the chief town of an arrondissement and seat of a sub-prefect. It is beautifully situated on a rocky hill rising above the gorge of the Cance, a tributary of the Sélune. The parish church of St Évroult is a magnificent example of the transitional style of the early 13th century, with a massive tower of the 14th and a Norman doorway dating from the original collegiate church (1058). Close to the town is the Abbaye-Blanche, founded as a Benedictine convent in 1105 and soon afterwards affiliated to Cîteaux. The church is a perfect example of a Cistercian monastic church of the late 12th century, and portions of the 12th-century cloisters also survive. The population is between 2000 and 3000.

Mortain was, in the middle ages, the head of an important comté, reserved for the reigning house of Normandy. In or about 1049 Duke William took it from his cousin William, “the warling,” and bestowed it on his half-brother, Robert, thenceforth known as “count of Mortain,” whose vast possessions in England after the Conquest (1066) gave name to “the small fees of Mortain,” which owed less (knight) service than others. Robert was succeeded as count by his son William, who rebelled against Henry I., was captured at the battle of Tinchebrai (1106) and forfeited his possessions. Some years later, Henry bestowed the comté on his nephew Stephen, who became king in 1135. On Stephen’s death (1154) his surviving son William became count of Mortain, but when he died childless in 1159 the comté was resumed by Henry II. On the accession of Richard I. ( 1189 ) he granted it to his brother John, who was thenceforth known as count of Mortain till he ascended the throne (1199). With his loss of Normandy the camté was lost, but after the recapture of the province by the House of Lancaster, Edmund Beaufort, a grandson of John of Gaunt, was created count of Mortain and so styled till 1441, when he was made earl of Dorset.

As the counts are often described as “earls” of Mortain (or even of “Moreton”) the title is sometimes mistaken for an English one. It has also, through erroneous spelling, been sometimes wrongly derived from Mortagne-en-Perche.

 MORTAR, the name (1) of a vessel in which any material may be crushed or pounded, and (2) given to various compositions used in building and consisting of lime and cement with sand or other fine aggregate, well mixed by manual labour or machinery with a proper quantity of clean water (see below, and also ). The Latin name both for such a vessel and for the material as mixed in it, is mortarium. The earlier English form morter, from Fr. mortier, has been in modern English more closely adapted to the spelling of the Latin original. As applied to a vessel, the name is chiefly used for one employed in the preparation of drugs, which are pounded or triturated in the “mortar” by means of a pestle (Lat. pistillum; pinsere, to pound). The name has also been given, from a resemblance in shape to the vessel, to a short thick piece of ordnance, resting on a “bed” formerly used for high-angle fire. The barrel was always very short, normally even shorter than it was wide, and sometimes even resembled a bowl in shape. The place of the mortar in artillery is now taken by the howitzer. In modern times the name “mortar” is occasionally used for a particularly short howitzer. (See .)

Building Mortar.—The sand forming the aggregate is placed on the mixing platform and formed into a ring within which lime in the required proportion is placed; it is then gently but thoroughly sprinkled with clean water through the rose of a watering-can or hose-pipe. The lime is covered with the sand and left undisturbed for a day or two to slake, and the whole mass is then turned over and well mixed with the larry. The mortar is often used immediately the materials are thoroughly incorporated, but it should rather be kept covered over with sacks until well tempered. For large works a mortar mill working by hand, steam, or other power effects a considerable economy. Stone chippings, clean, hard, broken bricks or furnace clinkers may take the place of sand when the mill is employed, as the action of grinding reduces any large pieces to small sandlike particles.

The remarks above apply to ordinary lime mortar. Mortar of hydraulic lime, cement mortar, or mortar gauged with cement, must be mixed up in quantities sufficient only for immediate use. Any material not used at the time, or at least the same day, will be wasted; cement cannot be reworked after it has begun to set as its setting properties are destroyed.

Slaking is a most important part in the process of making mortar. There are three methods of slaking lump lime—the first by immersion, the second by sprinkling with water, and the third by exposing the lime to the atmosphere and leaving it to absorb moisture. Different qualities of lime require varying amounts of water, but the average quantity is about a gallon and a half to

every bushel of lime. It should be all added at one time and the mass then left to slake undisturbed. Hot limes are often used for mortar. These are unsuitable for plastering unless slaked for a long period. It will at once be seen that when mortars composed of these limes are used immediately after mixing, slaking must continue for a long time, drying up the moisture necessary for setting, and causing the mortar to crumble to dust in the joints of the brickwork. This fact gives us the reason for the old Roman enactment which set forth that lime should be slaked for three years before using. In the south of Europe it is the custom to slake lime the season before it is used.

The practical application of mortar to building work, and the methods of pointing the joints of brickwork and stonework, are described and fully illustrated in the article on.

The results of many careful tests and experiments serve to show that the hardening of mortar is due to several causes acting collectively. With ordinary lime mortars the chief causes of hardening are the absorption of carbonic acid from the air and the combination of part of the water with the lime, which unites with some of the silica of which the sand is composed and

forms silicate of lime. The initial setting is due to the evaporation of the excess of water and to the production of minute crystals of hydrate of lime which slowly absorbs carbonic acid gas from the air. With mortar of rich lime an outer crust is thus formed on the exposed parts which prevents ready access of air to the interior and retards setting. In illustration of this peculiar property of lime to remain soft, some remarkable cases may be mentioned. One of the bastions erected by Vauban in 1666 was removed by General Treissart, in 1822, a hundred and fifty six years after erection. The lime in the interior of the masonry, where it was inaccessible to the action of the atmosphere, was found to be quite soft. Dr John of Berlin mentions that in removing a pillar 9 ft. in diameter in the church of St Peter, Berlin, eighty years after erection, the mortar in the interior was found to be quite soft. Sir C. W. Pasley, in removing the old wharf wall at Chatham dockyard in 1834, found that the work executed in lime mortar was easily removable, the mortar being in a state of pulp. The brickwork, built with Roman cement, it was found necessary to blast.

The Romans were convinced that it was owing to prolonged and thorough slaking that their works in plaster became so hard and were not defaced by cracks. L. B. Alberti mentions in his writings that he once discovered in an old trough some lime which had been left there five hundred years and that it was quite soft and fit for use. The setting and hardening of hydraulic limes and cements are due mainly to crystallization brought about by the action of water on the silicate of lime, and not by mere absorption of carbonic acid gas from the atmosphere. As a consequence we find that this variety of limes and cements has the valuable property of setting hard while immersed in water and in many cases growing increasingly hard with the lapse of time.

Opinions differ very widely on the question of the suitability for building purposes of limes or cements which contain an appreciable proportion of magnesia, many experts holding the view that the expansion which often occurs in floors and other works of concrete from one to four years after laying may be justly attributed to the presence of this substance. For mortars,

however, it may be assumed that the presence of magnesia is not detrimental to the value of the matrix, but on the contrary may be a source of strength, for experiments show that it reduces the energy of