In cutting _precious stones_ with use of lead discs lead poisoning frequently occurs, especially where this trade, as in some parts of Bohemia, is carried on as a home industry. The authorities have required substitution of carborundum (silicon carbide) for lead discs. As, therefore, an efficient substitute is possible, use of lead should be prohibited. Similarly, use of lead in the making of musical instruments should, if possible, be discontinued. Brass pipes in _musical instrument_ making are filled with lead to facilitate hammering and bending, and in this way poisoning has occurred. In numerous other industries where the use of lead cannot be avoided, and where consequently the danger must be present, as, for instance, in _lead melting_, _soldering_, _lead rolling_, _stamping_, _pressing_, &c., in the manufacture of _lead piping_, _shot_, _wire_, _bottle capsules_, _foil_, _toys_, and many other articles, general preventive measures should be carefully carried out. _Melting of lead_ and _lead alloys_ should be carried out only under efficient exhaust ventilation. In larger works where dust is generated this should be drawn away at the point where it is produced. This applies also to processes in the chemical industries where lead or lead compounds are used, seeing that no substitute is possible. Zinc, Brass-casting, Metal Pickling, Galvanising (See also pp. 151 and 182) In zinc smelting account has to be taken of fumes which may contain lead, zinc, arsenic, sulphur dioxide, and carbonic oxide. Metallic fumes require to be condensed—a procedure in harmony with economic interests. This is effected in a technically arranged condensing system, consisting of a condenser and prolong, in which the fumes are given as large a space as possible in which to condense and cool. In order to prevent the entry of fumes into the shed when removing distillation residues, hoods should be arranged over the front of the furnace through which the gases can be conducted into the main chimney stack or be drawn away by a fan; in addition the residue should fall into trolleys which must either be covered at once or placed under a closely fitting hood until the fuming contents are cool. As the mixing of the materials for charging and the sifting and packing of the zinc dust (poussière) may cause risk, these processes require to be carried out mechanically with application of local exhaust. Such an arrangement is shown in fig. 59 below. The material which is fed in is carried by the elevator to the sifting machine, falls into the collecting bin, and is then packed. The points at which dust can come off are connected with the exhaust and carried to the dust collector; fans carry the filtered air to the outside atmosphere. [Illustration: FIG. 59.—Arrangement for Sieving and Packing Zinc Dust (poussière). _a_ Charging hopper; _b_ Distributor; _c_ Elevator; _d_ Sieve; _e_ Collector; _f_ Packing machine; _g_ Exhaust pipe; _h_ Worm; _i_ Dust Collector; _k_ Motor]