The plaster stone of the Paris basin contains about 12 per cent. of carbonate of lime. This body, ground and mixed with water, forms an adhesive mortar much used in building, as it fixes very speedily. Works executed with pure gypsum never become so hard as those made with the calcareous kind ; and hence it might be proper to add a certain portion of white slaked lime to our cal cined gypsum, in order to give the stuc co this valuable property. Colored stuc cos of great solidity are made by adding to a clear solution of glue any desired coloring tincture, and mixing in the pro per quantity of the calcined calcareous gypsum.
The compact, fine-grained, gypseous alabaster is often cut into various orna mental figures, such as vases, statuary groups, cke., which take a high polish and look beautiful, but from their soft ness are easily injured, and require to be kept enclosed within a glass shade.
In America and France, the virtues of gypsum in fertilizing land have been highly extolled.
Pure gypsum consists of lime 28, sul phuric acid. 40, water 18, which are the respective weights of its prime equiva lent parts.
M. Gay Lussac, in a short notice on the setting of gypsum, says that the purest plasters arc those which harden least, and that the addition of lime is of no use toward promoting their solidity, nor can the heat proper for boiling gyp gum ever expel the carbonic acid gas from the calcareous carbonate present in the gypsum of Montmartre. He con ceives that a hard plaster-stone having lost its water, will resume more solidity in returning to its first state than a plas ter-stone naturally tender or soft ; and that it is the primitive molecular ar rangement which is regenerated.
Franklin was the first to call public at tention to the use of gypsum as a ma nure, and by the experiment of sowing it in the form of letters on a field, which when the grass grew could be read by its superior growth and verdure, tested fully its value. It is now justly considered indispensable to good farm ing, but it exerts its chief value only on dry or drained soils. Sands and learns feel its influence at once. Two pecks on sandy soils and fifteen bushels on clays have been applied : the farmers of Western New-York look upotawo bush els per acre as sufficient. It is chiefly valuable to leguminous plants, as pease, beans, clover, saintfoin, and lucerne. It should be sown broadcast in spring when the young leaves are started ; it then throws turnips on to grow so quick that they escape the ravages of the fly. On account of dissolving so sparingly in water, it is best sown in wet weather. Calcined gypsum after being moistened with a solution of alum, and again burn ed, acquires much greater hardness and solidity. A Mr. Kreating has recom mended for the same purpose a solution of 1 lb borax in 9 lbs. of water, which is poured over the calcined fragments of gypsum. They are then kept at a strong red heat for six hours, ground to a pow der, and worked. The effect is better if a lb. of tartar and twice the quantity of water were added to the solution.