What are corrosives?Corrosives are materials that can attack and chemically destroy exposed body tissues. Corrosives can also damage or even destroy metal. They begin to cause damage as soon as they touch the skin, eyes, respiratory tract, digestive tract, or the metal. They might be hazardous in other ways too, depending on the particular corrosive material.

Most corrosives are either acids or bases. Common acids include hydrochloric acid, sulfuric acid, nitric acid, chromic acid, acetic acid and hydrofluoric acid. Common bases are ammonium hydroxide, potassium hydroxide (caustic potash) and sodium hydroxide (caustic soda).

Other chemicals can be corrosive too. Check the supplier labels on chemical product containers.

It is wise to treat unknown materials as very hazardous until they are positively identified.

Corrosive materials are present in almost every workplace. Acids, bases (which include caustics or alkalis), and other chemicals may be corrosive. Everyone who works with corrosives must be aware of their hazards and how to work safely with them.

Please see the OSH Answers How Do I Work Safely with Corrosive Liquids and Solids? for more information.

How are corrosives hazardous to my health?Corrosives can burn and destroy body tissues on contact. The stronger, or more concentrated, the corrosive material is and the longer it touches the body, the worse the injuries will be.

Some corrosives are toxic and can cause other health problems. Check the MSDS and label on the container for warnings of other possible health effects.

An example is the chemical glutaraldehyde. It has been used as a disinfectant and sterilizing agent in medical and dental settings as well as other uses. It is harmful if inhaled or swallowed. Glutaraldehyde can be irritating or corrosive to the respiratory tract, eyes and skin. It may cause permanent eye injury. It is also a skin sensitizer as it may cause (severe) allergic skin reactions.

How are corrosives hazardous to my eyes?Corrosive materials can severely irritate, or in come cases, burn the eyes. This could result in scars or permanent blindness. The stronger, or more concentrated, the corrosive material is and the longer it touches the eyes, the worse the injury will be.

How are corrosives hazardous to my skin?Corrosives touching the skin can severely irritate or even badly burn and blister the skin. Severe corrosive burns over a large part of the body can cause death.

How are corrosives hazardous when I breathe them in?Breathing in corrosive vapours or particles irritates and burns the inner lining of the nose, throat, windpipe and lungs. In serious cases, this results in pulmonary edema, a buildup of fluid in the lungs that can be fatal.

How are corrosives hazardous to my digestive tract?Swallowing corrosives burns the sensitive lining of the mouth, throat, esophagus and stomach. In nonfatal cases, severe scarring of the throat may occur and could result in losing the ability to swallow.

What is hazardous when corrosives touch metals?Many corrosives attack and corrode metals. Contact with corrosives can damage containers, equipment, installations and building components made from unsuitable materials. The rate of metal corrosion is greater when the corrosive is stronger and the temperature is higher. When acids attack metals, hydrogen gas is often given off. This is a flammable gas which can burn or explode if an ignition source is present.

Common bases, such as sodium hydroxide and potassium hydroxide, can also attack some metals like aluminum, zinc, galvanized metal, and tin to produce hydrogen gas. The MSDS for a particular corrosive should explain which metals or other materials, such as plastics or wood, it will attack.

Are there other hazards associated with corrosives?Some corrosives are also flammable or combustible and can easily catch fire and burn or explode.

Some corrosives are incompatible with other chemicals. They may undergo dangerous chemical reactions and give off toxic or explosive products if they contact each other.

The MSDSs and the labels on the containers should explain all of the hazards for the corrosive materials that you work with.

What Defines A Corrosive Environment?

 

A corrosive environment can consist of many different corrosive elements. Not all corrosive pollutants are found in a single corrosive environment. It is also rare for a corrosive environment to have only one corrosive pollutant in its atmosphere. The more aggressive the environment, the more critical the selection of proper protective coating becomes.

Along many coastal regions, rising populations have increased energy demands and local atmospheric corrosion from automobile fumes, fertilizers, animal and insect fluids and other corrosive contaminants. Concrete, steel, most alloys, structures and facilities; industrial, commercial and residential equipment including air conditioning coils, all require corrosion protection from the abundance ofcontaminants found in the atmosphere. Even at substantial distances from the ocean, structures and equipment are susceptible to salt water contamination.

Aftermarket investment in a quality corrosion-resistant coating is usually less costly than unit or coil replacement, inefficient unit operation, constant unit maintenance, discomfort or lost production costs. The savings gained is found in extended structure or equipment life, lower maintenance costs, better operating efficiency and reduced service expenses.

 

Various Types Of Corrosive Pollutants Or Atmospheres In Different Environments

Marine/Industrial: (Severe) This combination of corrosives is often found on off-shore oil drill rigs or in industrial coastal locations. It is a combination of marine and industrial pollutants including, salt air, hydrogen sulfide, carbon dioxide, ammonia and others. 

Coastal/Marine (Severe) Salt air, acid rain, automobile emissions, animal, bird and insect fluids, and sulfur water.

Suburban/Rural: (Mild-Heavy) Generally these atmospheres include automobile emissions, varying levels of ammonia, nitrogen, fertilizers, and fluids from birds, insects and animals (such as urine and feces), all of which are corrosive.

 

Many processing facilities such as wastewater treatment plants, pulp paper mills, chemical plants, refineries and others create gases in their processing. Many of these gases are highly corrosive, including methane, hydrogen sulfide, chlorine, sulfur dioxide, and others. Though most are in low parts per millions concentrations, nevertheless they are airborne corrosives which have a corrosive effect on the structures and equipment within their environment.

Corrosion Facts • Corrosion is the deterioration of a substance (usually a metal) or its properties because of a reaction with its environment.• Polluted air is more corrosive than clean air.• Moist air is more corrosive than dry air.• Hot air is more corrosive than cold air.• Hot water is more corrosive than cold water.• Salt water is more corrosive than fresh water. • Sulfur in a mist of warm air is a common corrosive found in fossil fuel plant environments. • Acids are generally more corrosive than bases (alkalis).

• In sugar refining corrosion or spalding of concrete is a continual concern.• The by-products of various food processing procedures are often highly-corrosive.• Corrosion is a natural consequence of an element's temporary existence in metallic form. • There are more than 50 specific types of corrosion, although there are only a few mechanisms which are common to all of them.• Of the 105 elements known to man, about 80 of them are metals. • Corrosive atmospheres are found in every environment and range from mild to severe. • The only place where corrosion will not occur is in a vacuum.

Types of Corrosive Atmosphere

While atmospheres can be classified into four basic types, most environments are mixed and present no clear demarcation. Furthermore, the type of atmosphere may vary with the wind pattern, particularly where corrosive pollutants are present, or with local conditions such as illustrated in the following Figure.

Bird damage to a 1931 bronze statue commemorating the 21st Battalion battles in WWI.

Industrial

An industrial atmosphere is characterized by pollution composed mainly of sulfur compounds such as sulfur dioxide (SO2), a precursor to acid rain, and nitrogen oxides (NOx), the backbone of smog in modern cities. Sulfur dioxide from burning coal or other fossil fuels is picked up by moisture on dust particles as sulfurous acid. This is oxidized by some catalytic process on the dust particles to sulfuric acid which settles in microscopic droplets and fall as acid rain on exposed surfaces. The result is that contaminants in an industrial, atmosphere, plus dew or fog, produce a highly corrosive, wet, acid film on exposed surfaces.

In addition to the normal industrial atmosphere in or near chemical plants, other corrosive pollutants may be present. These are usually various forms of chloride which may be much more corrosive than the acid sulfates. The reactivity of acid chlorides with most metals is more pronounced than that of other pollutants such as phosphates and nitrates.

Example problem 9.1

Are industrial sites near where you live more corrosive than adjacent locations? Provide some examples.

Marine

A marine atmosphere is laden with fine particles of sea mist carried by the wind to settle on exposed surfaces as salt crystals. The quantity of salt deposited can vary greatly with wind velocity and it may, in extreme weather conditions, even form a very corrosive salt crust, similar to what is experienced on a regular basis by sea patrolling aircraft or helicopters as shown in the following Figure.

a)

b)

Sea salt deposited on the external surface a) of a Cormorant sea and rescue helicopter radar antenna, and b) salt causing corrosion to the antenna internal

components due to a broken seal. (courtesy Major S.J.R. Giguère)

The quantity of salt contamination decreases with distance from the ocean, and is greatly affected by wind currents. The marine atmosphere also includes the space above the sea surfaces where splashing and heavy sea spray are encountered. The equipment exposed to these splash zones are indeed subjected to the worst conditions of intermittent immersion with wet and dry cycling of the corrosive agent as illustrated in the followingFigure.

Aircraft carrier top deck. (courtesy Mike Dahlager, Pacific Corrosion Control Corporation)

Rural

Rural atmospheres are typically the most benign and do not contain strong chemical contaminants, that is unless one is close to a farm operation where byproducts made of various waste materials can be extremely corrosive to most construction materials.

Arid or tropical atmospheres are special variations of the rural atmosphere. In arid climates there is little or no rainfall, but there may be a high relative humidity and occasional condensation. This situation is encountered along the desert coast of northern Africa. In the Tropics, in addition to the high average temperature, the daily cycle includes a high relative humidity, intense sunlight, and long periods of condensation during the night. In sheltered areas, the wetness from condensation may

persist long after sunrise. Such conditions may produce a highly corrosive environment.

Indoor

Normal indoor atmospheres are generally considered to be quite mild when ambient humidity and other corrosive components are under control. However, some combinations of conditions may actually cause relatively severe corrosion problems. While there is no typical contaminant or set of conditions associated with an indoor atmosphere, any enclosed space which is not evacuated or filled with a liquid can be considered an indoor atmosphere. If not ventilated, such an environment may contain fumes, which in the presence of condensation or high humidity could prove to be highly corrosive.

Example problem 9.2

Indoor corrosion has caused many unpleasant surprises. Find some examples close to your immediate surrounding.

Even in the absence of any other corrosive agent, the constant condensation on a cold metallic surface may cause an environment similar to constant immersion for which a component may not have been chosen or prepared for. Such systems are commonly encountered in confined areas close to ground level or, worse, below ground where high humidity may prevail. The following Figure shows the advanced corrosion of the frame and contacts in an electric junction box only four years after a building was completed. While the junction box in this example was only at the ground level, the wires coming to the box were buried without additional insulation and in constant contact with much cooler ground than ambient air in the room.

Electric junction box badly corroded only four years after a new residence was completed.

CORROSIVE CHEMICALS

What Is the Scope of This Guideline?

This guideline identifies general safety precautions that should be reviewed and followed when dealing with corrosive chemicals at Brandeis. They represent a significant hazard because skin or eye contact can readily occur from splashes, and their effect on human tissue generally takes place very rapidly.

Examples of corrosives:

Glycolic acid Imidazole 4-Methoxybenzylamine Sodium hydroxide Amines Sulfuric acid Bromine Hydrogen peroxide

Corrosive gases and vapors are also extremely hazardous. Examples which can cause severe irritation and bodily injury include:

Ammonia Hydrogen chloride Nitrogen dioxide Sulfur dioxide

How Do I Protect Myself?

Review the material safety data sheet (MSDS) prior to using this material.

Eye ProtectionSafety glasses that meet the ANSI Z.87.1 1989 standard should be worn whenever handling corrosive chemicals. Ordinary prescription glasses WILL NOT provide adequate protection unless they also meet this standard. Safety glasses should also be equipped with side shields if there is a possibility of flying particles (i.e., glass, plastics). When there is the potential for significant splash hazards, additional eye/face protection should be worn in the form of goggles or a face shield.

Skin ProtectionGloves should be worn when handling corrosive chemicals. Nitrile gloves should be adequate for handling most of these in general laboratory settings. An MSDS should be reviewed if handling may involve extended or high exposure to lab personnel to ensure adequate skin protection is provided.

In addition, a lab coat or apron is advised if exposure could involve more than normal handling operations would be expected. No open-toe shoes are allowed.

Special Handling

Never store corrosive liquids above eye level. Always add acids or bases to water (and not the reverse). Segregate acids and bases in storage. When mixing corrosive solids with water, always slowly add the corrosive solid to the water,

stirring continuously. Cooling may also be necessary. If there is a possibility that you may generate a significant amount of dust, conduct work in a fume

hood. If the potential exists for explosion or a high thermal reaction, additional shielding should be

utilized. This may involve the use of shielding in a glove box or in the case of a fume hood with the sash in the lowest possible position. Portable shields may also be used for additional protection.

Store corrosives material away from heat/flames, oxidizers and water sources. Keep containers closed and ensure that manufacturer’s labels and warnings remain intact.

Special Considerations for Corrosive Gases

For potentially corrosive gases, perform manipulations of materials that pose an inhalation hazard in a chemical fume hood to control exposure or wear appropriate respiratory protection.

Ensure that you protect all exposed skin surfaces from contact with corrosive or irritating gases and vapors.

Ensure that regulators and valves of gases are closed when the cylinder(s) are not in use and properly purged and cleaned with dry air or and inert gas such as nitrogen.

Ensure that when corrosive gases are to be discharged into a liquid, a trap, check valve or vacuum break device is employed to prevent dangerous reverse flow.

Handling Emergencies Involving Corrosive Chemicals

Anticipate emergency situations, have proper handling equipment in the lab and readily available for spills. Acid and base spill kits are available in the Main Hazardous Waste Accumulation area. Contact the Department of Environmental Health and Safety at ext. 6-4262 or the Hazardous Waste Hotline (Monday/Thursday) at ext. 62561 for access. It is also highly recommended that spill control material/kits be maintained in the lab.

In the event of a spill or adverse reaction, notify lab personnel immediately that an incident has occurred. Do not attempt to handle a large spill/reaction/fire, or one in which you are not trained or equipped for.

Laboratory emergencies should be reported to public safety at ext. 6-3333. Public safety will also contact the Department of Environmental Health and Safety at ext. 6-4262. Communicate the following:

Location of spill/incident Type of material involved and quantity Injuries involved Fire/explosion Your location/contact information (or who to contact for further information)

Notify the principal investigator or designated safety officer as soon as possible.

Waste Disposal Requirements

Handling and disposal of corrosive chemicals should be done in accordance with lab protocol established by the principal investigator. 

Aqueous solutions between pH 6.0 to 10.0 may be disposed of down the sink. Contact the Department of Environmental Health and Safety at ext. 6-4262 with any question concerning sink disposal of material other than aqueous solutions described here. The university operates under a discharge permit from the Massachusetts Water Resources Authority and has specific discharge limits.

Disposal requests should be called into the Waste Hotline at ext. 6-2561.

Decontamination Procedures

Cleanup and decontamination may require the use of neutralizing agents. Review the MSDS for additional guidance and personal protection

Our men throw acid in our faces, destroy our lives but we never stop loving men. (Warning: Violent images)Men throw acid on us with the intention of injuring or disfiguring us. Men throw acid on our bodies,

burn our faces, smash our noses, melt our eyes, and walk away as happy men.

Acid attack is common in Pakistan, Bangladesh, India, Afghanistan, Nepal, Cambodia, and a few

other countries. Men throw acid on us because men are angry with us for ending relationships and

for refusing sexual harassment, sexual exploitation, proposals of marriage, demands for dowry. They

throw acid on us for attending schools, for not wearing Islamic veils, for not behaving well, for

speaking too much, for laughing loudly.

India

She was 18, a college student. Three of her neighbors sexually harassed her for more than two

years and then threw acid on her. Her skin on the skull, face, neck, chest and back were melted

away. After nine years of that attack Sonali Mukherjee is now blind in both eyes and partially deaf.

Her father spent millions of rupees for her treatment. They have now no money. The attackers got

bail from the High Court, continued threatening to kill her. She is now asking the government to help

her or allow her to end her life.

Cambodia

The face of Sokreun Mean, who was blinded and disfigured by an acid attack.

Carsten Stormer, a German journalist & photographer said,

“Acid attacks deprive people of more than their looks and sight. Families are torn apart. Husbands

leave their wives. Children are separated from their parents. Jobs vanish overnight, turning

professionals into beggars. Many victims cannot get through a day without constant assistance,

becoming burdens on their families. All bear the mark of the pariah.

“What remains is a traumatized society in which domestic disputes, unhappy love affairs, and

professional rivalries are nearly always resolved through violence. Hardly a family without its

members lost to the ideological battles of the Khmer Rouge – a curse that is passed on from parents

to children. Battery acid is known to be most uncomplicated way of causing lifelong suffering. A

dollar will buy you a quart of acid on any street corner. The perpetrators are seldom punished. Their

targets become outcasts.”

Pakistan

Fakhra Younus was attacked by her husband Bilal Khar, ex-MPA of the Punjab Assembly and the

son of Pakistani Politician Ghulam Mustafa Khar. He threw acid in her face after they split up.

Tehmina Durrani, the author of ‘My Feudal Lord’, the former step mother of Bilal Khar tried to help

Fakhra. She was sent to Italy for treatment. After having 39 re-constructive surgeries, Fakhra

committed suicide.

The stories of the girls, from left to right:

Ten years ago Shahnaz Bibi was burned with acid by a relative due to a familial dispute. She has

never undergone plastic surgery. Najaf Sultana is now 16. At the age of five Najaf was burned by her

father while she was sleeping. Her father didn’t want to have another girl in the family. Najaf became

blind. Shameem Akhter (20) was kidnapped and raped by a gang of men who then threw acid on her

3 years ago. Kanwal Kayum, now 26, was burned with acid one year ago by a man whom she

rejected for marriage. Bashiran Bibi was burned at her husband’s house just after her marriage.

Nasreen Sharif was a beautiful girl. When she was 14, her cousin poured a bottle of sulphuric acid in

her face. He did it because he couldn’t stand boys whistling at her when she crossed the street. Her

skin melted away, her hair burned away. She is now blind, she has no ears and she has no sense of

smell.

Among others, there is Shaziya Abdulsattar, an eight-year-old girl. Shaziya’s father threw acid on her

and her mother Azim last year after the mother refused to sell their two boys to a man in Dubai to

use as camel racers.

BangladeshIt is very easy for a man to get sulphuric acid if he wants to attack a woman he does not like. The

country has become a hot spot for acid attacks. A disfigured woman is not able to get married or get

a job. She becomes a financial and social burden on her family.

Neela was forced to marry when she was 12 years old. Her husband threw acid on her face when

she was 14. He was angry with Neela because her family was unable to give him the dowry money

he asked for.

Nepal

Akriti Rai, 22, was attacked by her husband, a Nepali soldier.

Iran

Ameneh Bahrami rejected the offer of having a relationship with Majid Movahedi, a fellow student at

the University of Tehran. He then threw a bottle of acid in her face.

Zambia

A man threw acid on a 13-year-old girl’s face to take a revenge. The older sister of the girl said: “You

have to grow crocodile skin to clean the wounds of an acid survivor. The worst ordeal was while in

the hospital, as the skin kept peeling off. I didn’t realize that the tongue skin was also peeling off.

The young girl was pushing something in her mouth. I opened her mouth to see and found that

almost the whole tongue had come off. I had to pull it out like you do with a cow and only a little red

thing (tongue) remained.’

Nitric acid, sulphuric acid, hydrochloric acid are today’s weapons of choice for criminals who hate

women. These acids are easy to buy, easy to hide, easy to carry, and easy to throw. A person who

witnessed many acid attacks , said, ‘in a less than a minute the bone under the skin can start to be

exposed. If there is enough acid, the bone itself can become a soft mass of non-distinguishable jelly.

Internal organs can dissolve. Fingers, noses and ears can melt away like chocolate on a hot day.’

Ethiopia

Twenty-one-year-old woman Kamilat Mehdi’s life was changed forever when a stalker threw

sulphuric acid in her face. Ismail, Kamilat’s brother said: “The man who attacked her stalked her for

a few years. He gave her a hard time but she didn’t tell the family for fear that something would

happen to them. He was always saying he would use a gun on them.” Ultimately the stalker’s

weapon of choice was not a gun, but a bottle of acid. He used it on Kamilat and destroyed her entire

life in one second.

UK

Her lover did it. Richard Remes threw sulphuric acid on Patricia Lefranc. Her nose and eyelids were

melted away, she lost sight in one eye and hearing in one ear, she also lost a finger. She came

close to death, as the corrosive substance nearly burned through her heart and lungs.The horrific

attack physically and emotionally scarred her for life. What was her crime? She ended her

relationship with Richard Remes, a married man.

We are more abused, harassed, exploited, kidnapped, raped, trafficked, murdered by our lovers, husbands, fathers, brothers, uncles, cousins, friends, or men we know well than by strangers. Whatever happens to us, we never stop loving men.

He made me a monster": Sulphuric acid victim faces attacker in court

Mar 13, 2012 13:24 By Natalie Evans

Patricia Lefranc was left horrifically disfigured after she was ambushed by jilted lover Richard Remes in December 2009

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ReutersPatricia Lefranc arrives at Justice Palace to attend the trial of Richard RemesScarred for life: Patricia Lefranc was left horrifically disfigured in the attack

A mother who was left horrifically disfigured after her jilted lover sprayed her in the face with acid has faced her attacker in court.

Patricia Lefranc was ambushed by her married ex-lover Richard Remes as she stepped out of a lift in December 2009.

The 48-year-old spent three months in a coma after her face and upper body were sprayed with sulphuric acid.

ReutersPatricia Lefranc arrives at Justice Palace to attend the trial of Richard RemesFacing her attacker: Ms Lefranc arrives at court in Brussels

The vicious attack left her blind in one eye and partially deaf and she has been forced to endure 86 operations.

But brave Ms Lefranc attended court in Belgium today and said she was “determined to look him in the eye and show the jury what he has done to me”.

Remes, 57, is standing trial in Brussels accused of attempted murder for the attack, which happened in the suburb of of Molenbeek-Saint-Jean.

ReutersLawyer Daniel Spreutels and Victim Patricia Lefranc attend the assize trial of Richard Remes, before the Assize Court of BrusselsSupport: Ms Lefranc had lawyer Daniel Spreutels by her side in court

ReutersDaniel Spreutels, lawyer of Patricia Lefranc, waits for the start of Richard Remes' trial in a court in Brussels"Monster": The 48-year-old told the court how Remes has "ruined" her life

Ms Lefranc claims Remes intended to kill her after she ended their two year affair.

Revealing that she is mocked by her son’s school friends and stared at in the street, Ms Lefranc reportedly said: “Remes has also ruined my life as a woman.

“Who wants to deal with the monster that he made me?”

ReutersEvidence, including a bottle of sulfuric acid and a photo of Belgian woman Patricia Lefranc, is displayed at the start of Richard Remes' trial in a court in BrusselsEvidence: The bottle of sulphuric acid and a photo of Ms Lefranc is shown to the court

Photo NewsRichard RemesAccused: Richard Remes claims he did not know the attack would have such devastating consequences

More than two years after the attack, the acid continues to erode Ms Lefranc’s skin, eating away at her nose which will eventually have to be replaced with a prosthesis.

She was quoted as saying: “When I look in the mirror, every fibre of my body reminds me of what happened.”

Remes has apologised for the attack but denies that he intended to maim her, claiming he did not realise the acid would have such a devastating effect.

The trial continues.

`

ention part of your sample) will fly out of the flask and possibly onto your hand. 

The image on the left shows the results of just such a spattering five days after it occurred. This student was 

holding a flask with the rubber Hot Hand and as the flask was removed, it "bumped", splattering her hand. The student washed her hand immediately with copious 

quantities of water and the instructor helped her to rub a slurry of sodium carbonate all over the spots. She then went to the student health center for treatment, but the 

hot concentrated acid had already done its work. The use of crucible tongs, as shown on the right, is a safer method for moving around flasks containing these solutions. 

A similar spattering occurred recently in which five seconds passed between the time the droplets of hot nitric and sulfuric acid spattered onto the student's arm and hand and when she began rinsing off the acid in copious quantities of running water. The top pair of photos show where the droplets hit minutes after it happened. She thereafter visited the Student Health Center for medical treatment.

One week later.

Two weeks later.

So as not to leave anything to chance, we can't emphasize too strongly that strong acids are to be treated with respect and care. The image on the right shows the result of a splash and extended contact of 3M sulfuric acid six months after it occurred. The student was working in a non-university laboratory. His supervisor spilled and splashed some 3M sulfuric acid but was not aware that any had gone beyond the immediate work bench area. The student was standing a few feet away. An hour after the splash occurred the student felt a burning sensation near his ankle. He was wearing elastic sweat pants with direct contact with his skin in that area. When he tried to pull up his pant leg to find out what was causing the burning sensation he noticed that the fabric had bonded (more or less) to his skin at the place producing the burning sensation. He realized what had happened and soon thereafter cut away the bottom of his pant leg and sought medical treatment. The remaining scar is a good indication of the long-lasting appearance of such an injury. 

Any acid which contacts the skin must be washed off immediately. Acid which dribbles down the outside of laboratory stock bottles offers a familiar peril to students who use bottles of reagents in common. One is not immediately conscious of such contact because even in the case of concentrated acids there is some delay before the reaction between acid and skin raises the temperature sufficiently for one to feel the effect. Students are advised to be conscious at all times of potential mishaps caused by their procedures and to be prepared to take immediate and appropriate action. If fingers or other areas having exposed skin feel wet when they ought not to be wet, the surface should be washed immediately in running water. The images at the left and right show the effect of either concentrated sulfuric or nitric acids which stayed on the skin for more than a few seconds (but less than a minute) before being washed off. Fortunately most discolorations caused by such contact disappear within a few days, but constant 

vigilance in the laboratory is the rule which should be followed at all times. 

Continuing with the presentation of helpful hints, the presence of the concentrated sulfuric acid aids in the exclusion of the remaining nitrogen oxides from the hot solution. Those red oxides first boil off, then one sees fumes of sulfur trioxide beginning to escape, as at the left