[MUSIC] Well, arsenic and thallium are well known in toxicology. They've got a long track record of use in poisoning. So in a poisoning case, these are things that people might look for. But many other elements are also poisonous but are not very well known and therefore. When there is such a case, no analysis is done for these more exotic elements. And one example would be the element barium. Barium poisoning is actually very very uncommon partly because very few people actually have access, two compounds containing barium. One person who used barium poisoning was a young lady called Marie Robards in the City of Mansfield in Texas. And presumably because of family problems she put some barium acetate in her father's dinner, it was Mexican food. Whether she planned to kill him or not, she probably didn't plan to kill him, but she may have just used too much barium acetate, and her father died. It wasn't suspected that it was murder, So he was buried, and Marie continued with her life. She went onto university, and she took some classes at university. And in one of those classes they were studying the play by Shakespeare, Hamlet. And it was actually William Shakespeare that caught out Marie Robards. Now part of the play Hamlet, an important part concerns the murder of Hamlet's father. And this got to Marie and she confessed to one of her friends that she had murdered her father by putting something in his dinner. And it was this friend who then went to the police and the investigation started. So the victim was exhumed and analysis showed sure enough the presence of barium in his body. So Marie was convicted. She received a jail sentence and now I understand she's been released, and is living under a new identity. Barium, as I said, is not something that anybody can find. And it turns out that Marie had stolen it from her school chemistry laboratory. Now one use of barium is in medical x-rays. So you know very well that if you have a broken arm or something like that, you'll be x-rayed and a doctor can see a picture of your bones very nicely. A very important tool for diagnosis. But suppose you have something wrong for instance, with your stomach or your intestines. These are all soft tissues, they don't show up on X-rays. But a technique was developed, so that the intestines could be visualized by X-ray. And this use what we'll call barium meal and barium meal contains barium, the patient eats it so their intestines are full of barium, and that means that when the patient is X-rayed, the intestines will how up nicely and the doctor can do a diagnosis. So why doesn't barium meal poison the patient? The reason is quite simple, barium meal uses barium sulfate. Barium sulfate is highly insoluble in water. Which means that even though your intestines are stuffed full of it, it's not absorbed into the body. If it's not absorbed into the body, it can't reach any target organs and therefore no poisoning takes place and the barium is ultimately excreted in the normal course of events. Marie Robards on the other hand, she used soluble barium acetate, it's soluble and therefore it's easily absorbed