We have had many enquiries lately respecting the mastic cement for covering the fronts of houses and giving them the appearance of brown freestone. We have endeavored to find out its composition, and have at last, we believe, obtained reliable information respecting it. Red lead, oil, sand, and limestone dust, in some form, ,.over every compound of it. 50 parts by measure, of clean dry sand ; 50 of limestone (not burned) reduced to grains like sand, or marble dust, ad 10 parts of red lead, mixed with as much boiled linseed oil as will make it slightly moist, compose a mastic cement. The building of brick to receive it should be covered with three coats of boiled oil laid on with a brush, and all suffered to dry, before the mastic is put on. It is laid on with a trowel like plaster, but it is not so moist. It becomes as hard as ston in tl? iOurpe of a few months. Care must be exercieed not to use too much oil—although no evil will be the result—excepting that the cement will require longer exposure to harden. The oil prevents rain and moisture penetrating, and this is the reason why this mastic is not affected with the weather. Various compositions will answer about as well as the receipt above. We will present a few. 100 parts (by measure) of clear dry sand; 100 parts of powdered limestone, and 5 of red lead, make a hard mastic ; this may be varied with the addition of 10 parts of red lead. 100 parts of sand, 50 parts of whiting, and 10 of red lead make a moderately hard cement. 100 parts of sand, 25 parts of the plaster of Paris (or the same of marble dust) 10 parts of red lead, and 5 parts of yellow ochre, make a very beautiful and hard cement. As stated before, all of these compositions must be moistened with boiled linseed oil. The quantity of oil is so very small in proportion to the other materials, that the whole mass is very porous. The oil unites the particles together, it is the affinitive agent. The sand, &c, must be perfectly dry before they are mixed together ; that is, they must be subjected to heat ill an oven to drive off all the water contained in them. The sand should not be too coarse and should be passed through a fine sieve. Vari-ious coloring substances may be employed to mix with the above composition, such as any of the pigments used in oil painting. We would never use less than 10 parts of red lead in the cement. The above compositions might be moulded into statues and works of art, by oiling the patterns inside, before putting in the composition and allowing the mastic to harden in the moulds before it is removed. Two ounces of rosin pounded very fine should be added for every pint of oil used. The whole must be mixed with great care to make the cement properly. Steam engines for agricultural purposes have increased ten-fold in the last three jears ? in England.