C E M addition of water : this compound may prove of considerable service in making troughs for holding wa- ter, or lining small canals. A cheap mortar, or cement, that will not crack, may also be procur- ed, according to M. Wiegleb, by mixing three parts of the thin re- siduum after slackingthe lime, with -one of powdered gypsum ; but he adds, that it can be used only in dry situations. A peculiar kind of cement is pre- pared at Madras, with which most of the buildings erected in that In- dian capital, are cemented. It consists of sand and lime, with the addition only of a small quantity cf water, in which a proportion of coarse sugar has been previously dissolved. The quick-setting of tliis mortar, and the great hardness it acquires, can, as Dr. James An- derson has observed (in his Re- creations in Agriculture, vol. i.), only be attributed to one of these two causes, namely, either the su- gar added, or the quality of the lime-stone employed at Madras. — There are some kinds of lime-stone in Britain, which afford a much better mortar than others ; and this also may be the case in India. Most calcareous earths are blend- ed with sand and other particles, in various proportions ; the quality of the mortar or cement will con- sequently vary, according to the nature of these different ingre- dients. It has lately been discovered, that the scrapings of certain roads, consisting chiefly of levigated lime- stone, which is impregnated in a greater or less degree with the dung and urine of animals, form an excellent cement. For ordinary wails, these scrapings alone are frequently used ; and, according CEM [477 to the account of Mr. Marshall (in his Rural Economy of Glouces- tershire), the proportion for the best building is about one part lime to three of those materials, collecV ed from roads composed of lime- stone. By the ingenuity of speculative men, however, several other modes of forming cements, have been contrived and successfully em- ployed ; but the enumeration of these would necessarily lead us to a greater length than our lifn'hs will permit. We shall, therefore, only give an account of the prin- < ipal Patents lately granted for the inv ntion or various cements. The first, is that of Mr. iotas Worth, chemist, dated the 2Sra of May 17/1, now expired; for a " Preparation, or cement, for tin? purpose of preserving His Majesty's and other ships and vessels from worms, &:c. and for various pur- poses in agriculture and com- merce." — This composition con- sists of fourteen pounds of powdered or small pieces of resin; twenty- eight of sand, sifted and washed clean from dirt or loam; three and a half of red lead ; and one p an I three quarters of oil: the resin must be melted over a moderate fire, the sand and lead gradually put in, and then the oil ; care being taken, when they are boil- ing, to stir them constantly till they become cold, so that the mass may be uniform. When there is occasion to use this cement, the quantity required must be broken into small pieces, and a pound of what is usually denominated by the chemists, fat oil, mixed with every twelve pounds of it. As as soon as this is melted, it may be applied to the object intended,
- • bv pouring it on, or by a
brush,
