In operating thus, all the remaining ammonia that might have escaped the condenso-purifier is removed, and the result is obtained without pumps or motor, with apparatus that costs but little and does not occupy much space. The advantages that are derived from this, as regards sulphate of ammonia, are important; for, on treating ammoniacal waters with condensers, scarcely more than four to five kilogrammes of the sulphate are obtained per ton of coal distilled, while by washing the gas perfectly with the small quantity of water indicated, four to five kilogrammes more can be got per 1,000 kilogrammes of coal, or a total of eight to ten kilogrammes per ton. When the gas is not washed sufficiently, almost all of the ammonia condenses in the purifying material. The pressure absorbed by the condenso purifier is from ten to twelve millimeters per washing-diaphragm. In works that are not provided with an extractor, two diaphragms, or even a single one, are employed when it is desired simply to catch the tar. The apparatus under consideration was employed in the St. Quentin gas works during the winter of 1881-1882, without giving rise to any obstruction; and, besides, it was found that by its use there might be avoided all choking up of the pipes at the works and the city mains through naphthaline. In cases of obstruction, it is very easy to take out the perforated diaphragms; this being done by removing the bolts from the piece that holds the register, f, and then removing the diaphragm and putting in another. This operation takes about ten minutes. The advantages of such a mounting of the diaphragms is that it allows the gas manufacturer to employ (and easily change) the number of perforations that he finds best suited to his needs. These apparatus are constructed for productions of from 1,000 to 100,000 cubic meters of gas per twenty four hours. They have been applied advantageously in the washing of smoke from potassa furnaces, in order to collect the ammonia that escapes from the chimneys. In one of such applications, the quantity of gas and steam washed reached a million cubic meters per twenty-four hours.--_Revue Industrielle._ * * * * * ARTIFICIAL IVORY. It is said that artificial ivory of a pure white color and very durable has been manufactured by dissolving shellac in ammonia, mixing the solution with oxide of zinc, driving off ammonia by heating, powdering, and strongly compressing in moulds. * * * * * CREOSOTE IMPURITIES. [Footnote: Read at the meeting of the American Pharmaceutical Association held at Niagara Falls. 1882.] By Prof. P. W. BEDFORD. The object of this query can be but one, namely, to inquire whether the wood creosote offered for sale is a pure article, or not; and if not, what is the impurity present?