A number of acids are regularly used in photography, and in most cases there is little risk involved. Acetic acid 28%, commonly used in stop baths, fixers, and elsewhere when a mild, buffered acidulant is needed, is hardly dangerous if spilled on the skin. Bisulfites (actually metabisulfites) are typically mildly acidic and present no large risk. Boric-acid, citric acid, succinic acid, and tartaric acid are all mild organic or so-called "vegetable" acids which are safe enough to form a part of our diets, sometimes in surprisingly high concentrations. But even the organic acids may cause problems at high enough concentrations, and glacial acetic acid should be considered corrosive and treated with care. Oxalic acid is an organic acid used in photography and it is quite poisonous. But of greater concern are the mineral or inorganic acids. For our uses these are hydrochloric, nitric, and sulfuric acid. Any of these are capable of causing skin burns or blindness, and the fumes of nitric or hydrochloric acid may cause damage if inhaled. Very small quantities may cause severe and extremely painful damage to the gullet and windpipe if ingested. Sulfuric acid when mixed with water may overheat locally and splatter. Hydrofluoric acid is a special case; it not only is capable of burning the skin or eye, but will temporarily anesthetize the area so that one does not know the burn is occurring and therefore does not move to clean the area.
When handling acids one should have good ventilation, immediate access to running
water, and proper
protection for the eyes. We recommend goggles, especially when handling concentrated acids. Always
remember the basic rule of diluting acids:
ADD ACID TO WATER, NEVER ADD WATER
TO ACID.
IN CASE OF EXTERNAL CONTACT: Wash promptly with copious quantities of water. Flood without scrubbing until the area is completely clean. This is usually adequate, but a mild salve may help if actual burning has occurred. Treat as a burn -- as there is essentially no difference.
IN CASE OF INTERNAL CONTACT: Immediately treat to neutralize the acid with whiting, magnesia, chalk, or wall plaster. Small pieces of soap softened in water, milk or raw egg whites may be taken. Do not induce vomiting. CALL A PHYSICIAN AT ONCE.
IN CASE OF EYE CONTACT: Do not stop to call for help. Immediately flood the eye with water for at least five minutes. This must be done before calling the doctor. Stick your head under the faucet and turn on the water, holding the eye open with the fingers of one hand.. You can adjust the water temperature with the other hand so that it is not uncomfortable. A gentle stream of water is best. CALL A PHYSICIAN AS SOON AS POSSIBLE.
With ordinary and reasonable care, acids may be made safe to handle. Only carelessness and exceptional circumstances make them dangerous. The individual worker must take the responsibility to be prepared for the exceptional and prevent carelessness. While it is easy to spill a drop of concentrated acid on the hand while measuring, it is also easy to take steps to prevent truly risky contact, as with the eye or when taken internally. Clean up spills with wet paper towels. Store acids in hard to reach places with tight lids. Keep away from children, and store so that glass bottles cannot be broken. In the case of glacial acetic acid, prevent freezing which occurs at about 16°C/60°F.
Hydroxides that are commonly used in photographic practice include Ammonium Hydroxide solution, Lithium Hydroxide, Potassium Hydroxide, and Sodium Hydroxide. Each of these chemicals, in solid or liquid form, is extremely caustic. Since caustic materials by definition are capable of dissolving protein, including animal tissue, one should understand the behavior of these materials and the proper techniques for handling them.
Solutions of the hydroxides, if spilled on the skin, will slowly dissolve it, and if splashed in the eye, can cause blindness in a short time. The dry material is hydroscopic, and will absorb water from the air or body to form a caustic liquid very readily.
IF HYDROXIDES CONTACT THE SKIN: Wash the area thoroughly with running water until the slipperiness is no longer present. Slipperiness is due to the hydroxide dissolving the skin. If desired, rinse with a vinegar or working strength acid stop bath. Wash thoroughly. Treat damaged tissue as a burn.
IF HYDROXIDES CONTACT THE EYE (dry or wet): Place your head at once under running waster (the sink is fine) and wash the eye for 5 to 10 minutes. Don't bother with eye washes, etc. Time is all important. WASH THE EYE FIRST, then call a doctor at once.
To dissolve the hydroxide, simply stir the pellets into the solvent. It will dissolve very readily. It will not be necessary to pulverize the pellets or flakes. Large amounts of heat are liberated when hydroxides are dissolved, and if care is not taken, glass ware may be broken or spattering may occur. It is prudent to dissolve a portion of the hydroxide, allowing the solution to cool before proceeding. Use cold or ice water when dissolving hydroxides.
Be sure to pick up all the pellets that accidentally spill. The solid material will pick up moisture from the air and in time, a very concentrated, very caustic solution forms. Dispose of hydroxide solutions by flushing down the sink or toilet with large amounts of water.
Since damage to flesh or eye can be serious, we strongly suggest the use of safety glasses and gloves when handling caustics. The use of beakers with handles is advantageous, as they are less likely to be dropped, The most important safety precaution is to take the time to move deliberately and carefully. Caustics should not be handled in the presence of children or pets.
All substances can be dangerous. Any material can be handled with safety if the correct precautions are followed. In many years of handling caustic solutions and other potentially hazardous chemicals, we have had no serious difficulty, and with a reasonable amount of care, you need have no problems. We counsel respect, but not fear.
Sulfides of different kinds are used in photography, with sodium sulfide and polysulfide most often used in toning processes. We need to be aware of three particular areas of risk with sulfides. They may be dangerous as caustic solids or liquids, or as a very poisonous gas, and the fumes will fog photo-sensitive emulsions. A solution of sulfide will dissolve flesh, and if allowed to contact the eye blindness may result. A very small dry particle of sulfide will, upon reaching the eye, immediately form a concentrated solution with body fluids: IF SULFIDES IN ANY FORM SHOULD CONTACT THE EYE IMMEDIATELY PLACE YOUR EYE UNDER RUNNING WATER FOR 5 TO 10 MINUTES. Don't waste time calling for help or looking for eye washes, administer first aid at once and then call a physician. Time is all important.
It is always prudent to dissolve caustics in cold water, as considerable heat may be involved. It is as well, when making concentrated solutions, to dissolve the sulfide a bit at a time or to use ice water. The fumes of sulfide solution are very noxious, but when a sulfide contacts an acid, the gas generated by the reaction is not only evil-smelling, it is an exceptionally powerful poison. The gas, hydrogen sulfide, is as active as hydrogen cyanide, and should be treated with equal respect. The only safe way to work with this gas is under near-ideal conditions, so it is essential that acids and sulfides not be allowed to contact each other in significant quantities. Dispose of spent solutions in a working drain with copious amounts of water. Never allow a sulfide to follow an acid into a drain, or vice versa. To do so will allow the poisonous gas to be generated in the sewer, and to be backed-up into the home. Promptly clean up any suIfide or acid spill to avoid accidental contact.
We recommend the use of goggles when using sulfides or caustics of any sort. With reasonable precautions, suIfides may be safely and profitably used, as they have been for many generations.