When bare metal is employed, the action of the metal on the bath, as well as that of the bath on the metal, has to be considered. In particular, copper and tin, 2 with their alloys (with the exception of the copper-nickel alloy to be mentioned), bronze, brass, and solder, should never come into contact with a developer, owing to the certainty of an intense chemical fog (J. I. Crabtree, 1918).
In considering the choice of a metal, a dis tinction must be drawn between a material suitable for amateurs, which is not likely to be ex posed for long periods to chemical action, and one used on a commercial scale, which may be almost continually in contact with the solutions used.
Stainless steel for chemical industries (with i8 per cent chromium and 8 per cent nickel), pure nickel, nickel alloys rich in nickel (Monel, Inconel) are suitable for development, fixation and washing ; copper or brass thickly and evenly nickel-plated, are suitable for vessels used for development and washing ; they may also be used for fixation, but the time of exposure to hypo must be strictly limited to the time neces sary for fixation, and the vessels must be washed immediately afterwards.' Tanks of cast iron and of mild steel have been used with advantage for developers with a strong content of caustic alkalies.
Lead is not attacked by developing or fixing solutions (the latter may contain acid, alum, or silver salts), nor does it affect the solutions. 2 Wooden tanks lined with lead (the joins must be made by welding and not with a tin solder) are very satisfactory, as are small lead-lined steel tanks. Type metal has similar properties., and may be used, particularly for taps in photo graphic tanks.
Zinc is not affected by pure water, but it is rapidly attacked by photographic solutions, even when very dilute. When tanks for washing are made of or lined with zinc, it is essential to restrict the corrosion of the metal by at least rinsing plates or prints before putting them into the tank. The tank should always be emptied and drained after use. With some care, tanks of galvanized iron may, however, be used for slightly alkaline developers.
In general, all metal vessels which come into contact with developing or fixing solutions should be made of one homogeneous metal.
Of two metals in contact with each other and with the solution, one is always more quickly corroded than it would be alone, owing to galvanic action. Most alloys thus suffer greater corrosion in contact with solutions than would either of the constituents separately.' 265. Glass-ware. The photographic outfit comprises a number of glass articles, notably graduated glasses (measuring glasses, conical glasses, and measuring the gradua tions of which are often marked with a pleasing disregard of exactness (the graduation of meas uring cylinders is generally less crude than that of the conical measures, and is, at any rate, fairly uniform), stirrers' (glass rods rounded at the two ends by heating), a dropping bottle,' and funnels for filtrations. In a dark-room of any size a funnel stand of wood is a useful thing the " notch " type is preferable to the " ring " pattern.
For the preparation of baths it is useful to have some pots or pans of enamel ware or aluminium in which water may be heated, the dissolution of the chemicals being done in a. bottle or 'n some vessel of a material resis tant to the substances used. For warming-up any solutions, basins of porcelain or pyrex glass, or, more economically, porcelain kitchen casseroles, should be used exclusively.
We shall discuss more fully in a later chapter the question of bottles and glass jars (§ 271).
266. Cleaning of Utensils. Dishes, tanks, and all vessels or utensils of glass or earthenware are best cleaned by running a little strong hydrochloric acid all over. The acid can be used a great number of times. With a bard brush or a rubber sponge it is then very easy to remove all adherent deposits, and the clean ing is finished by rinsing in pure water and draining. It is better not to wipe ; the cloth used is generally dirtier than the vessel to be cleaned.
If a point is made of cleaning vessels immedi ately after use, it is usually sufficient to rinse them in water to be sure they are perfectly clean.
Adherent deposits on the inside of bottles can often be removed by shaking up with lead shot.