In the linotype machine, matrices are brought down from the magazine by touching the corresponding letters on the type indicator until they are arranged so as to form the line; a lever then carries them sideways into position, so as to allow the molten metal to flow into the mould and cast the line. Another lever then raises the matrices, which are carried into the magazine again, the slab of metal with the cast line upon it falling into a receptacle. Here, again, danger of lead fume is hardly in question. As the matrices drop down from the magazine, particles of lead which they have gathered when in contact with the metal are detached, and are visible on every linotype machine at this point. The brass cover of the magazine, if not frequently cleaned, soon becomes coated with fine dust. Although lead fume may not be given off, it is none the less necessary to remove the products of combustion from the heating apparatus, in order to prevent constant vitiation of air and to reduce the temperature in the neighbourhood of the machines. Monotype machines give off much heat. Exhaust ventilation by hoods reaching well over the pots, and branch ducts entering the main duct in connection with a fan tangentially, can alone accomplish this satisfactorily. Hoods and ducts leading merely into a shaft running up the side of the building fail to prevent condensation of the water vapour, which in consequence trickles back. Wherever a well-thought-out system of exhaust ventilation has been installed, reduction in temperature and comfort to the operatives has been secured. Temperatures above 65° F. must incommode a linotype operator. [Illustration: FIG. 11.--EXHAUST VENTILATION ON THE PATENT “PENTARCOMB” PRINCIPLE APPLIED TO METAL MELTING-POTS, ETC., IN PRINTING FOUNDRY, AS INSTALLED BY THE ZEPHYR VENTILATING COMPANY, BRISTOL. P, Patent “pentarcomb” for equalizing exhaust; D, main and branch ducts; U, upcast from fan; F, fan; H, hoods over melting-pots and dross drums; S, stereo metal melting-pots; B, boxes or drums for dross. The illustration shows exhaust ventilation applied to the melting and stereo pots and dross drums in a letterpress printing foundry. The draught over each pot is equalized at the point where the branch ducts join the main duct by insertion of a patent “pentarcomb” grid, which breaks up the columns of air into numerous smaller channels by specially curved metal plates so as to minimize friction. The ducts are graduated, and the exhaust is provided by a volume fan.]