“For that matter it’s perfectly easy to make too. Any schoolboy knows how to treat benzol with nitric acid to get nitrobenzene. I’ve done it myself a hundred times. The veriest smattering of chemical knowledge is all that’s wanted, and nothing in the way of expensive apparatus. Or, so far as that goes, it could be done equally by somebody without any chemical knowledge at all; that is, the actual process of making it. Oh, and it could be made quite secretly by the way. Nobody need even guess. But I think just a little chemical knowledge at any rate would be wanted, ever to set one about making it at all. At least, for this particular purpose.
“Well, so far as the case as a whole was concerned, this use of nitrobenzene seemed to me not only the sole original feature but by far the most important piece of evidence. Not in the way that prussic acid is valuable evidence for the reason that prussic acid is so hard to obtain, because once its use was determined anybody could get hold of or make nitrobenzene, and that of course is a tremendous point in favour of it from the would-be murderer’s point of view. No, what I mean is that the sort of person who would ever think of employing the stuff at all ought to be definable within surprisingly narrow limits.”
Mr. Bradley stopped a moment to light a cigarette, and if he was secretly pleased that his fellow-members showed the extent to which he had engaged their interest by not uttering a word until he was ready to go on, he did not divulge the fact. Surveying them for a moment as if inspecting a class composed entirely of half-wits, he took up his argument again.
“First of all, then, we can credit this user of nitrobenzene with a minimum at any rate of chemical knowledge. Or perhaps I ought to qualify that. Either chemical knowledge, or specialised knowledge. A chemist’s assistant, for instance, who was interested enough in his job to read it up after shop-hours would fit the bill for the first case, and a woman employed in a factory where nitrobenzene was used and where the employees had been warned against its poisonous properties would do for an example of the second. There are two kinds of person, it seems to me, who might think of using the stuff as a poison at all, and the first kind is subdivided into the two classes I’ve mentioned.
“But it’s the second kind that I think we are much more probably dealing with in this crime. This is a more intelligent sort of person altogether.
“In this category the chemist’s assistant becomes an amateur dabbler in chemistry, the girl in the factory a woman-doctor, let us say, with an interest in toxicology, or, to get away from the specialist, a highly intelligent lady with a strong interest in criminology particularly on its toxicological side—just, in fact, like Mrs. Fielder-Flemming here.” Mrs. Fielder-Flemming gasped indignantly and Sir Charles, though momentarily startled at the unexpected quarter from which was dealt this tit for the tats he had lately suffered at the gasping lady’s hands, emitted the next instant a sound which from anybody else could only have been described as a guffaw. “All of them, you understand,” continued Mr. Bradley with complete serenity, “the kind of people who might be expected not only to keep a Taylor’s Medical Jurisprudence on their shelves but to consult it frequently.
“I agree with you, you see, Mrs. Fielder-Flemming, that the method of this crime does show traces of criminological knowledge. You cited one case which was certainly a remarkable parallel, Sir Charles cited another, and I am going to cite yet a third. It is a regular jumble of old cases, and I am quite sure, as you are, that this is something more than a mere coincidence. I’d arrived at this conclusion myself, of criminological knowledge, before you mentioned it at all, and I was helped to it as well by the strong feeling that whoever sent those chocolates to Sir Eustace possesses a Taylor. That is a pure guess, I admit, but in my copy of Taylor the article on nitrobenzene occurs on the very next page after cyanide of potassium; and there seems to me food for thought there.” The speaker paused a moment.
Mr. Chitterwick nodded. “I think I see. You mean, anybody deliberately searching the pages for a poison that would fulfil certain requirements … ?”
“Exactly,” Mr. Bradley concurred.
“You lay great stress on this matter of the poison,” Sir Charles remarked, almost genial. “Do you tell us that you think you’ve identified the murderer by deductions drawn from this one point alone?”
“No, Sir Charles, I don’t think I can go quite so far as that. I lay so much stress on it because, as I said, it’s the only really original feature of the crime. By itself it won’t solve the problem, but considered in conjunction with other features I do think it should go a long way towards doing so—or at any rate provide such a check on a person suspected for other reasons as to turn suspicion into certainty.
“Let’s look at it for instance in the light of the crime as a whole. I think the first thing one realises is that this crime is the work not only of an intelligent person but of a well-educated one too. Well, you see, that rules out at once the first division of people who might be expected to think of using nitrobenzene as the poisoning agent. Gone are our chemist’s assistant and our factory-girl. We
