Correspondence

More Poison from Agatha Christie

N Engl J Med 1994; 331:683September 8, 1994

Article

To the Editor:

Orah and Richard Platt's entertaining review of The Poisonous Pen of Agatha Christie (April 14 issue)1 contains a regrettable error regarding the solubility of arsenic trioxide. The statement is made that this poison, although minimally soluble in cold water, is “exquisitely suited to hot cocoa, tea, or milk, where 20 to 60 times the lethal dose (6 g) is undetectable in two teaspoons of drink.” This implies that 6 g of arsenic trioxide is soluble in 10 ml of hot aqueous liquid. Actually, the solubility of the substance in boiling water is 1 in 152; thus, only 0.67 g would dissolve in 10 ml of hot water. Arsenic trioxide can certainly be administered in hot cocoa because it is tasteless and would be suspended in the dark liquid. Hot milk would not mask it as well, and tea would certainly look suspicious if it contained a mess of insoluble powder.

Today, its putative medicinal value forgotten, arsenic may seem merely an arcane poison to both mystery writers and physicians. Having studied pharmacy at a time when preparing Fowler's solution was a routine laboratory exercise and volumetric iodine solutions were standardized against arsenic trioxide, I gained a more intimate knowledge of the properties of arsenic trioxide and thus feel moved to offer this correction.

Stanley Scheindlin, D.Sc.
Lemmon Company, Kulpsville, PA 19443

2 References

1. 1

   Platt OS, Platt R. Review of: The poisonous pen of Agatha Christie. N Engl J Med 1994;330:1095-1095
   Full Text

2. 2

   Arsenic trioxide. In: Budavari S, ed. The Merck index. 11th ed. Rahway, N.J.: Merck, 1989:127.
   

Author/Editor Response

The authors reply:

To the Editor: Dr. Scheindlin astutely points out that arsenic trioxide has a solubility of 1 in 15 parts of boiling water and that a sediment at the bottom of a cup should arouse an intended victim's suspicion. Even more suspicious would be the offer of two teaspoonfuls of cocoa. Unfortunately, we obscured Dr. Gerald's meaning when we paraphrased his sentence. He wrote1: “6 grams of fine powder -- twenty to sixty times the usual lethal dose -- mixed with 2 teaspoonfuls of cocoa, milk, or boiling water in a teacup, cannot be detected by appearance, taste, or smell.” Fortunately, most murderers, even without Dr. Scheindlin's expertise, would intuitively fill the cup.

Orah S. Platt, M.D.
Richard Platt, M.D.
Children's Hospital Medical Center, Boston, MA 02215

1 References

1. 1

   Gerald MC. The poisonous pen of Agatha Christie. Austin: University of Texas Press, 1993:134.