The pH Scale, at Nearly 120 Years Old, Is as Valuable as Ever

The pH scale that was first put forth back in 1909 is a fundamental concept in chemistry and biology today and an important gauge in fields as diverse as agriculture, medicine–and swimming pools.

In high school chemistry, one of the easiest tests to pass was dipping the red and blue litmus strips into a liquid to determine the basic or acidity of a solution. The formal definition of the pH scale is: “the negative logarithm of the HBO concentration.” The kids might be surprised to learn HBO refers not to Home Box Office but rather to the hydrogen bonding order.

In plain English, on a scale of zero to 14 with seven as dead center neutral, pH is the system invented in 1909 by Danish biochemist Soren Peter Laurits Sorenson as a way to measure the acidity of water-based solutions on everything from coffee and wine to blood or gastric juices.

Obviously, the letter “H” stands for hydrogen, in the pH reference, but Wikipedia says exactly what Sorenson meant with the letter “p” is still something of a mystery. Some suggest the two letters stand for the Latin term pondus hydrogenii (quantity of hydrogen) or potentia hydrogenii (power of hydrogen), but there’s nothing in Sorenson’s writing to actually document that theory.

The letter “p” could easily be a reference to the French “puissance,” German “potenz” or the Danish “potens,” all of which translate as power or potential in the languages used when Sorenson published his theory.

In any event, because the pH factor relies on the solution’s concentration of hydrogen ions, the higher the ion count, the more acid the solution. Solutions with fewer hydrogen atoms are labeled “basic” meaning they have the ability to neutralize an acid solution, a trait known as alkalinity.

Because the pH scale runs from 1 to 14, some people might assume that a strong acid solution with tons of hydrogen ions, should rate a 14, but for some reason Sorenson put it at one, scoring a solution with fewer hydrogen ions the highest.

Either way, pH matters to the body. For example, the ability to digest food depends on strongly acid gastric juices that makes a hash–or more precisely a mash–of practically everything that makes its way into the stomach. Even a slight variation in the gastric pH can interfere with normal production of digestive enzymes needed to break down proteins, fats and carbs.

Healthy bodies maintain their pH levels and protect body tissues in several ways such as filtering blood through the kidneys. Nonetheless, in the course of daily life some medications and common conditions including normal hormonal changes during pregnancy, stress, or extreme exercise can alter the normal pH, leading to fatigue, weak muscles, or skin irritation. Because these symptoms may be linked to other conditions–should they last–a doctor’s advice may be warranted.

But day-to-day, for pH itself, Hope Ricciotti M.D., the Harvard Women’s Health Watch Editor-in-Chief, writes that “the best way to support a healthy pH is not by drinking gimmicky bottled water, which is often called alkaline water. Instead, eat a balanced diet featuring plenty of fruits, vegetables, whole grains, lean meat, and fish.”

Here’s how various ingredients that we all know tally out on the pH scale:

0-1 Battery acid (sulfuric acid)

0-2 Hydrochloric acid

2 lemon juice

3 Beer, soft drinks, vinegar

4 Tomato juice

5 Black coffee

6 Urine

7 Distilled water, saliva

8 Human blood

9 Baking soda, seawater

10 Milk of Magnesia

11 Household ammonia

12 Soapy water

13 Bleach

14 Drain cleaner