NetNotes


Edited by Bob Price University of South Carolina School of Medicine Bob.Price@uscmed.sc.edu


Picric Acid Disposal Microscopy Listserver Good aſternoon, we have found a bottle of old picric acid, which


someone may have been using for microscopy purposes a long time ago. Does somebody have a suggestion for disposal? Best regards, Antonio D. Molina-Garcia antoniom@ictan.csic.es


Around here, the university calls the local police department


bomb squad and shuts down the building until they dispose of the bottle. Literally and seriously. Tis has happened here. So, check with your organization’s hazardous waste people before even moving the bottle. Tere may be legal issues you have to face. Phil Oshel oshel1pe@cmich.edu


Same thing happened at one of my labs. During an inventory,


Safety found a 1lb jar of the stuff with a cracked lid. Te bomb squad shut down the building, took it out back (we were on the edge of town), and blew it up with C4. Tere was quite a thump when it was detonated. Tons of ensuing paperwork and chastisement for the lab supervisor. Becky Holdford pfadiva@gmail.com


Here is a link that you might find helpful, “Safe Handling of


Picric Acid”. https://ehs.wisc.edu/wp-content/uploads/sites/1408/ 2020/08/CHM-GUI-006-NEW.pdf. Bob Carter bobwcarter@ gmail.com


Out of curiosity, I looked it up. Picric acid is a high explo-


sive, slightly more powerful weight-for-weight than TNT. It was formerly used as the main charge in anti-tank rounds. I thought it was a primer only. A pound is a terrifying amount. Good thing whoever found it knew what they were looking at. Rick Mott rmott@pulsetor.com


It is also a contact explosive if it dries out. Hence the horror


at the cracked lid. In the distant past, some poor soul had the job of making sure it was kept damp. One pound is an extravagant amount; whoever ordered it originally made sure they had enough for an entire career. It was used ages ago as a component as a metal- lurgical etchant, but I was in a lab for 10 years and never once saw it used or even referenced. Becky Holdford pfadiva@gmail.com


My 2 cents: 1. Te simple approach. If you have it dry - keep it dry. If you have it wet - keep it wet. And keep it away from metals. I have a nice photomicrograph of grain boundary migration of picric acid coming out soon https://www.researchgate. net/publication/359865616_pH2_Postcard_2021_65_by_9_ R3_Sec.


2. From George Vander Voort: Picric Acid - Hazards and Safe Usage:


56 doi:10.1017/S1551929522000785


Picric acid (2,4,6-trinitrophenol, [(NO2


)3C6


H2


OH]) is widely


used in metallography labs for common steel etchants known as picral, a 4% solution in ethanol; Vilella’s reagent, 1 g picric acid and 5 mL HCl and 100 mL ethanol; and alkaline sodium picrate (2 g picric acid, 20 g NaOH, 100 mL water), for coloring M3C and M6C carbides, as well as several other formulations. Picric acid was for- mulated by Peter Woulfe, a British chemist, in 1771, although Glau- ber is claimed to have written about it in 1742. Te name comes from the Greek word pikros which means bitter, as picric acid has a bitter taste (it is toxic). Initially it was used to dye fabrics yellow. In the early 20th century, workers producing picric acid were some- times called canaries, because their skin became stained yellow. Te explosive nature of picric acid was discovered in 1885 in England, which led to the 1888 development of an explosive called Lyddite, named aſter the location of the studies, Lydd, England. Another source states that the explosive nature of picric acid was first known in 1830, and it was proven to detonate in 1873. In 1894, Russian scientists manufactured artillery shells using picric acid salts, and picric acid-based explosives were used in WWI. Anhydrous picric acid is related to TNT, a much more potent explosive. When con- centrated, it will attack metals, producing shock-sensitive salts that are explosive. Tis was discovered in 1916 at a French ammuni- tion factory when a fire caused molten picric acid to wet a concrete floor, forming calcium picrate, which detonated killing 170 people. Fortunately, there have been no documented cases of explosions from picric acid in laboratories, according to Phifer [1]. If it is wet with water, it is not an explosive hazard and any at-


tempt to blow it up by a bomb squad will only result in picric acid being spread all over the immediate area. Te concern has always been in finding an old bottle that has dried up producing dehydrat- ed picric acid, and if it has a metal cap, rather than a plastic cap. In such a case, shock-sensitive metallic picrates may have formed at the cap-bottle interface. Te solution is to have a robot pick it up and re-hydrate the picric acid aſter opening the bottle under water. If the cap is plastic, and the acid has dried out, friction from opening the cap could cause detonation. Te solution here is to place the bottle in a large bucket or tank of water and allow water to dissolve any dried picric acid on the cap threads. Leave the bottle in the water for a few days until some water can be seen inside the bottle. Ten, while under water, open the lid and re-hydrate the picric acid. Obviously, the wise lab manager checks the picric acid bottle


periodically (which can vary with lab usage of picric in etchants) to make sure that the picric acid remains wet. Today, bottles are sold with at least 30% water content. A good practice is to keep a log of when the bottle is checked and when water is added. Also, use only plastic or glass spatulas to remove picric from the bottle and add it to the etchant. Do not use metal spatulas and clean the cap and threads on the bottle and on the cap with a wet paper towel. If plumbing consists of copper piping, do not dispose of picric acid by pouring it down the drain as explosive metallic salts could form.


www.microscopy-today.com • 2022 July


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