Misdirection as to “Traces” of Arsenic
Out of the list submitted by the police, therefore, the only two things which could have been the source of the arsenic were the bottle of saturated solution, No. 10 in the Police List, and the bottle of solid arsenic, No. 11 in the Police List.
It may be observed that if all the arsenic or “traces” of the same, with which various things were said to be infected, were collected together, it would not constitute a fatal dose, the smallest fatal dose recorded being two grains, and this in the case of a woman, and surely not in the case of a person addicted to large doses of arsenic.
At the inquest Mr. Davies defined what he meant by the word “trace.” He said:
“It means something under 1/100 part of a grain. It does not mean something which I could not weigh, but something which I could not guarantee to be absolutely free from other things; but anything under 1/100 part of a grain I should not consider satisfactory. If I said distinct traces, I should say it meant something between 1/100 and 1/1000 part of a grain, while a minute trace is less than 1/1000 part of a grain.”
In reference to Reinsch’s test which Mr. Davies used in these experiments, this passage occurs in Taylor’s “Medical Jurisprudence,” vol. i., p. 268: “The mere presence of a gray deposit on pure copper affords no absolute proof of the presence of arsenic. Bismuth, antimony, and mercury all yield deposits with Reinsch’s test. The gray deposit of bismuth may easily be taken for arsenic.” And again: “The errors into which the faulty methods of applying Reinsch’s test lead have led its reliability to be much discredited, and, although in skilful hands the results are trustworthy, it would be perhaps unsafe to rely upon it in an important criminal investigation.”
It is submitted that the evidence relating to the articles which Mr. Davies said were infected with arsenic only to the extent of an unweighable trace could not and ought not to be regarded as proof that any arsenic at all was there, or as being anything more than a suspicion upon this analyst’s mind that what he saw was arsenic, and that it was a misdirection on the part of Mr. Justice Stephen to treat a mere expression of opinion of that kind as proof of the presence of arsenic.