would be injurious to the quality of the powder. The pulverization being deemed sufficient, the substance is sifted through a silk sieve, and then the remainder, with a new addition of flowers, is put in the mortar and pulverized again. The best vessels for keeping the powder are fruit jars with patent covers or any other perfectly tight glass vessel or tin box.--_American Naturalist_. * * * * * THE REMOVAL OF NOXIOUS VAPORS FROM ROASTING FURNACE GASES. In a paper read before the Aix-la-Chapelle section of the _Verein deutscher Ingenieure_, Herr Robert Hasenclever presents a summary of the results obtained with various methods for the absorption of the sulphurous acid generated during the roasting of zinc-blende and other sulphurets. Though most of our own metallurgical works are not so located as to be forced to pay much attention to the removal of noxious vapors, the efforts made abroad possess some interest for American metallurgists. Besides containing sulphurous acid, the gases from the roasting furnaces hold varying quantities of sulphuric acid, and Dr. Bernoulli describes a process applied on a large scale in Silesian zinc works, where the gases were passed through towers filled with lime. It was found that there was no trouble on account of the absorption of carbonic acid by the lime, and that the latter acted very efficiently in reducing the quantity of sulphurous acid. Before entering the tower, they contained 0.258 per cent. by volume of sulphurous acid and 2.45 per cent. of carbonic acid; while, after their passage through it, they held 0.017 and 2.478 per cent, respectively. The process, however, is declared by Herr Hasenclever to be too costly for ordinary working, although he does not deny its value under special circumstances. The removal of anhydrous sulphuric acid from the gases from roasting-furnaces has hitherto, as at the Waldmeister works, near Stolberg, been effected by means of water trickling down in a tower filled with coke, the gases entering below and moving upward. Herr Hasenclever tested the Freytag method, in which the water is replaced by sulphuric acid, and obtained favorable results, as shown by the following analyses of the gases before and after treatment. The figures given are grammes per 1,000 liters: BEFORE. AFTER. SO_2. SO_3. SO_2. SO_3. 8.24 0.63 5.74 0.00 8.29 0.37 6.74 0.07 9.36 0.69 6.96 0.00 9.46 0.63 7.38 0.05 10.03 1.08 7.69 0.09 16.52 2.97 14.39 0.23 17.90 1.97 13.32 0.11 17.80 2.46 16.18 0.69