MIXING,  TESTING,  AND  STORING EQUIPMENT The  type  of  material,  used  for  photographic chemical mixing, solution testing, storing, as well as film-handling equipment, must be considered before mixing  chemicals.  Materials  commonly  used  in  the construction of this equipment are Type 316 stainless steel, polyethylene, and glass. Related equipment, such as solution transfer lines, mixer shafts, impellers, and  machine  parts,  are  also  made  of  these  same materials. Some metals are not suitable for use with photo solutions. Serious chemical fog and developer changes can  be  caused  by  tin,  copper,  brass,  and  bronze. Aluminum, lead, nickel, zinc, galvanized iron, and Monel, when used with developers and fixers, can be harmful to films and papers. When these metals are used, silver thiosulfate from the used fixer may stick to them. Even when the utensils are washed after being in the  fixer,  enough  silver  thiosulfate  can  be  transferred  to the developer in the next processing or mixing run to cause stain, fog, or changes to image tone. Wooden paddles and other absorbent materials must not be used with photographic solutions. Once they have been used, it is almost impossible to wash them  clean  of  absorbed  chemicals. MIXING  CONTAINERS Chemicals should always be mixed in cylindrical containers made of suitable materials, The size of the mixing container should be suitable for the amount of solution to be prepared. A small batch of solution should  not  be  mixed  in  a  large  vessel  that  uses mechanical agitation because large amounts of air may be introduced, and splashing may occur. So, the mixing  container,  and  for  that  matter,  scales  and graduates,  should  be  sized  to  the  quantities  and volumes of solutions required. GRADUATES Graduates are used to measure liquids. Graduates are made in various sizes, calibrations, and of various materials.  The  units  of  measure  of  graduates  are calibrated in the U.S. liquid measurement system of ounces, quarts, and gallons, and in the metric liquid measurement system of cubic centimeters, milliliters, and liters. Glass is most commonly used for making graduates because it is NOT affected by most chemicals. Glass is also transparent and reasonably durable. Graduates are also made from plastic and stainless steel. When using graduates made of plastic, do not try to measure strong acids, such as sulfuric acid, which could cause severe damage. You must also be sure that the material the graduate is made of does not react with any of your photographic  chemicals. For  accuracy  in  measuring  liquids,  graduates should  be  proportional  in  size  to  the  quantity  of solution being measured; for example, an 8-ounce graduate  should  be  used  instead  of  a  32-ounce graduate to measure 2 or 3 ounces. When measuring a liquid in a glass graduate, hold it at eye level and pour the solution into it until the surface of the liquid reaches the correct mark. You will notice a curved surface on the top of the solution. This curved surface is called the “meniscus.” The correct amount is indicated by the lower of two visible lines of the meniscus (fig. 9-1). These two lines can be seen easily through the side of a glass graduate when it is held correctly. With an opaque graduate, such as stainless steel, the two lines can be seen by looking down into the graduate from an angle. Stop pouring the  solution  when  the  “lower  line”  of  the  liquid reaches the calibration mark. Major divisions are indicated by numbers on the graduate. Subdivisions are  shown  by  calibration  lines  only.  You  must determine the value of the individual subdivisions; for example, the marked or numbered lines may indicate ounces and read in series of 10. When there is only one calibration line between each graduation of 10, then the value of the calibration line is 5. THERMOMETERS All chemical action takes place faster at high temperatures   than   at   low   temperatures.   In   the photographic process, when you mix or use a solution, you must know its temperature. Thermometers  are  used  to  measure  the  temperature of the solution and may be made of glass or metal. The average glass thermometer consists of a bulb, containing either mercury or colored alcohol, attached to a capillary tube. This tube may be calibrated or it may be secured to  a  graduated  scale.  When  you  are  reading  a 9-2