Industrial use of arsenic compounds, in view of the risk attaching to them, should be reduced as much as possible. This has sometimes been achieved by technical improvement in processes of manufacture. Thus in the colour industry, where formerly colours containing arsenic played an important rôle, coal-tar colours have taken their place, and use of arsenic even in these (as in the manufacture of fuchsin) has been replaced by nitrobenzene. As the danger from arseniuretted hydrogen gas is especially great in processes in which acid acts on metal and either one or both of them contain arsenic, the materials, should be as free from arsenic as possible, in the production, for example, of hydrogen for soldering, in extracting metals by means of acids, in galvanic elements, in accumulator works, in the storage and transport of acids in metal vessels, and in galvanising. In any case the workers in these industries should be warned of the danger and instructed in case of emergencies. For soldering exclusive use of hydrogen produced electrolytically and procurable in steel cylinders is advisable. Extraction and Use of Gold and Silver In the extraction of gold and silver by amalgamation and subsequent volatilisation of mercury there is risk of mercurial poisoning. The preventive measures necessary are similar to those for poisoning in the recovery of mercury (see p. 327). _Argyria_ in pearl bead blowers can be avoided by using pumps to blow the silver solution into the beads instead of the mouth. In electroplating the possibility of poisonous fumes arising from the baths must be guarded against because hydrocyanic (prussic) acid, though only in minute quantities, may be evolved; care must be taken that the workrooms are well ventilated or the baths hooded. Careful personal hygiene is essential, for the prevention of skin diseases from which workers in electroplating often suffer. VII _PREVENTIVE MEASURES IN OTHER TRADES_ Ceramic Industry In the glass industry use of lead, chrome, and arsenic compounds should be restricted as much as possible or allowed only under suitable precautions (exhaust ventilation, personal hygiene, &c.). _Etching on glass_ by means of hydrofluoric causes almost inevitably injury to the workers. Rendering the surface of glass opaque should preferably be done by sand blast. When a bath of hydrofluoric acid for etching on glass is used the fumes require to be drawn away by hoods over the baths and the work-rooms well ventilated. Further precautionary measures are called for in view of industrial poisoning by furnace gases in various ceramic industries, as, for example, cement works, glass works, and tile works. The following suggestions are made in the technical introduction to the Germany Factory Act for prevention of poisoning from carbonic oxide, carbon dioxide, and sulphur dioxide: (1) Even the fixing of benches which might be used for sleeping on near the furnaces should be strictly forbidden;