It’s me again, the “bone collecting” teacher with a new question. How effective is rubbing alcohol in preserving specimens? Since I live at the beach, I am always finding marine specimens to use for student observations. Typically, I do not have any biological preservative available, so I’ve been using rubbing alcohol.
—Susan, Myrtle Beach, South Carolina
Many of us remember high school or college biology labs full of jars with preserved specimens and labels showing the name and when it was collected. They were interesting to look at, but the formaldehyde or formalin frequently used as a preservative in those days is a substance to be avoided today. In the NSTA Press book, Inquiring Safely, “Formaldehyde solution—also called formalin—has been replaced largely by newer, less odorous, and less toxic preservatives with a variety of trade names. However, most still contain formaldehyde, albeit in lesser concentrations and mixed with other ingredients. Treat all specimen preservatives as though they contain formaldehyde, particularly if you or your students are sensitive to materials of this type.” (p. 72)
In terms of alcohol as a preservative, I saw conflicting advice on the websites I examined. I contacted a friend of mine, Dr. Walter Meshaka, a zoologist and the senior curator of the section of Zoology and Botany of the State Museum of Pennsylvania. Here is his response to your question:
I advise strongly against formalin. You can use the standard 40% Isopropyl; however, a better choice, also to be found in most drugstores is ethyl alcohol. Additives keep it from being drinkable, so it is not ethanol [that is, it is] not white lightening. If available as stock (c.a. 95% or so strength) then dilute to about 70-75% and you’re good to go!
Whether you choose isopropyl or ethyl alcohol, be sure you have the appropriate Material Safety Data Sheet on file and use the appropriate safety procedures as you work with it (e.g., goggles and ventilation). Be sure the jars are securely sealed so inquiring fingers are discouraged from opening the jars.
I’ll put in a plug for specimens preserved in blocks of acrylic. Although they can be expensive to purchase, they last for many years and the students can handle them without worrying about breaking a jar.
For beachcombers, be aware of any regulations or required permits for specimen collecting. Some wildlife refuges or other parks and private beaches may have restrictions on taking things away from the beach.
As teachers, we all have collections of stories and anecdotes from our classes. In addition to her question, Susan and one of her students share a related story:
Things You Should Always Ask Your Students
During our study of animals, my sixth-grade students often bring in specimens to identify using our field guides. Shortly after Thanksgiving, Franklin brought in a jar containing a snake his father had killed in their yard. Since the snake had not been placed in a preservative, I suggested that we open the jar to add rubbing alcohol so we could include the specimen to our collection for observation. I had preserved specimens in the past using this method so was not concerned.
He and I opened the jar, and I immediately learned something you should always ask your students. The odor from the jar almost knocked us off our feet. The odor cleared every student out of my classroom, diffused down the 50-yard hallway (causing other teachers to rush out of their rooms), and finally made it to the principal’s office.
After reassuring the administration, teachers, and students that is was simply a matter of a stinky science classroom, everyone settled down. I expressed to Franklin my surprise about the overwhelming odor. Looking perplexed, he said, “Well, the snake has been dead since Halloween.”
So I learned one thing you should always ask your students: Just how long has the specimen been dead?