Thermometer factories

Occupational exposure to inorganic mercury is quite common, and occurs in the dental and chloralkali industries, as well as in thermometer factories, and in mercury mines. Approximately 70,000 workers in the United States are regularly exposed to mercury [16]. Measurements of mercury in blood and urine are useful in quantifying the magnitude of exposure (see section about biological monitoring below). In most instances there is a linear relationship between ambient air and urine concentration of mercury, where the urine... 

Occupational exposure to inorganic mercury has been investigated in chloralkali plants, mercury mines, thermometer factories, refineries, and in dental clinics. High mercury levels have been reported for all these occupational exposure situations, although levels vary according to work environment conditions. 

Richter ED Mercury exposure and effects at a thermometer factory. Scand J Work Environ Health 8 (suppl 1) 161-166,1982... 

Occupational exposure to mercury vapor occurs in a variety of industries such as chloralkali plants, thermometer factories, gold extraction process, and mercury mining. Dentists and dental assistants are also exposed to mercury vapor during insertion, polishing, and removal of amalgam fillings. 

In the free state, mercury is most poisonous as a vapor. Levels of mercury that exceed 0.05 mg Hg/m air are considered unsafe. Although we think of mercury as having a low vapor pressure, the concentration of Hg in its saturated vapor far exceeds this limit, and mercury vapor levels sometimes exceed safe limits where mercury is used— as in chlor-alkali plants, thermometer factories, and smelters. 

It is possible to check the calibration of a pipet, flask, or buret. The process involves weighing with a calibrated analytical balance. The volume of water (temperature noted) delivered or contained by the glassware is weighed. Then the analyst converts this weight to volume (using the density of water at the temperature noted), corrects the result to 20°C (the usual temperature of the factory calibration), and compares it to the factory calibration. If the difference is not tolerable, the piece of glassware is either not used for accurate work or a correction factor is applied. It should be pointed out that the thermometers used must be properly calibrated and that the timer used to measure the delivery time for the burets and pipets must also be calibrated. 

Note The water equivalent factor includes the heat capacity of the ensemble which includes the calorimeter itself, water bucket with water in it, supports of the bucket, bomb, thermometer and stirring device. These values can be calculated theoretically, but much more accurate results are obtained by combustion of a sample of standard material (such as benzoic acid, supplied by the US Bureau of Standards), the heat of combustion of which has been previously accurately determined. The water equivalent values of the calorimeters and bombs supplied by the Parr Instrument Co are determined by them at the factory... 

Temperatures below 12°C are not usually used, since crystallization of nitroglycerine could take place. Lower temperatures (e.g. 5-7°C) can be applied only when a mixture of glycerine with glycol or diglycerol is nitrated and if there exists no fear that the mixture of esters resulting from the reaction can freeze. In factory practice, nitration is performed mainly at temperatures of about 20-25°C or at 25-30°C. The temperature is measured by means of at least two thermometers, immersed in the vessel at different depths. 

In some factories the number of loose articles (e.g. bottles, buckets, thermometers) allowed in each house is also limited accidents have been caused by heavy objects dropping or falling. 

Children may be exposed to metallic mercury if they play with it. Metallic mercury is a heavy, shiny, silver liquid. When metallic mercury is spilled, it forms little balls or beads. Children are sometimes exposed to metallic mercury when they find it in abandoned warehouses or closed factories, and then play with it or pass it around to friends. Children have also taken metallic mercury from school chemistry and physics labs. Broken thermometers and some electrical switches are other sources of metallic mercury. Sometimes children find containers of metallic mercury that were improperly disposed of, or adults may bring home metallic mercury from work, not knowing that it is dangerous. 

In some thermometers, the so-called partial immersion thermometers, these corrections have been made at the factory. A partial immersion thermometer can be recognized by an engraved mark 76 mm from the bottom of the bulb. Such thermometers must always be immersed to this mark, and the stem must be kept at room temperature in order to have a precise reading. A partial immersion thermometer which is not immersed to its immersion mark, or which does not have the emerging stem at room temperature, still needs to be corrected by an expression analogous to that shown for total immersion thermometers. A final note of caution no temperature measurement is possible if the bulb is not safely immersed to the beginning of the constant-diameter capillary. 

In temperature indicators or thermometers the temperature is usually transmitted from a sensitive element to the dial by means of a capillary. It is important that this capillary is not kinked or bent or broken frequent flexing will easily cause the latter. Other indicating instruments in common use in chemical factories are ammeters, measuring electric current voltmeters for electric voltage liquid, vapour, and gas meters flowmeters pH meters weighing machines. 

The occupier of a humid factory is required to inform the factory inspector in writing when artificial humidity is first produced (s. 68). Every room in which artificial humidity is produced should have two hygrometers and a humidity table. The readings of the hygrometers shall be taken at certain times of the day and entered on the prescribed form, F48. Artificial humidification is not permitted in a room in which the wet bulb thermometer exceeds 22.5 C (72.5 F) or for certain processes 26.5 C (80 F) or when the difference between the readings of the dry and wet bulb thermometers is less than that indicated in the humidity table. No water which is liable to cause injury to health shall be used for artificial humidification. 

---