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parent liquid. A strong suspicion arising from other circumstances, inde- 
pendent of the chemist’s observation, that arsenic had been used as an 
instrument for committing the murder, it was the chemist’s business to 
determine whether any of the bottles contained arsenic or not. Any one will 
admit that Professor Taylor can be taken as a good example of the trained 
experimental observer ; but let us see what is required in him besides mere 
accuracy of observation. It was the case of Smethurst, which led to a great 
discussion at the time. Professor Taylor examined the fluid, which he sub- 
jected to a test which was conceived at that time to be a certain test to 
discover the existence of arsenic, and he went, and upon his oath, as a chemist 
before a coroner’s jury, said, “ I have examined this fluid, and I find that 
it contains arsenic” : and he gave the quantity of arsenic which should have 
been contained in the fluid. Now we cannot suppose that a trained observer 
would be careless in such a matter, or that, when asked on a question of life 
and death, he would consider it consistent with his duty to state lightly on 
oath, broadly and distinctly, that a certain fluid contained arsenic. Between 
the coroner’s jury and the trial of the man, however, certain doubts were 
suggested to Professor Taylor as to whether his analysis had been altogether 
accurate, and as to whether the fluid did really contain arsenic or not. What 
was the fact ? He had made use of a certain test which was considered to 
be infallible. It consisted in this, that if a suspected fluid containing arsenic 
is mixed with a certain quantity of hydrochloric acid and boiled in contact 
with bright copper, that bright copper receives a metallic, silvery-looking 
stain, and it is the chemist’s business to determine whether that stain contains 
arsenic or not by subliming the stain by applying the heat of a spirit-lamp 
until the stain evaporates, and little crystals are formed, and the chemist’s 
determination depends on the form of the crystal which is deposited. 
When Professor Taylor took copper to analyze this fluid he used copper-wire 
gauze. He found that the fluid contained something which caused the copper 
wire to dissolve. He kept on adding copper until the fluid no longer dissolved 
it, and then he submitted the solution to the further process, saying, “ Now 
I shall see whether the fluid will give me the arsenical stain or not.” It did 
give it, and he said, “ I put in so much copper ; therefore it must contain so 
much arsenic.” A suggestion was made to him — I believe by Mr. Graham, 
the late Master of the Mint — who said, “ Taylor, are you sure that you did 
not put in the arsenic yourself? Have you examined the copper you 
used, and are you sure that it contains no traces of arsenic ? ”, Pro- 
fessor Taylor upon that dissolved a piece of the wire gauze in a 
solution which he knew absolutely to contain no arsenic. He got the 
arsenical stain from that, and then he found that there was no copper which 
did not contain arsenic, and that there was not a particle of arsenic in the 
fluid he had analyzed. And he had the boldness and the honesty, when he 
came to that conclusion, to confess that he had been mistaken. That is one 
of those things which show how, as Mr. Reddie and Admiral Fishbourne 
have pointed out, what are supposed to be scientific facts turn out to be no 
facts at all. The fact to which Professor Taylor swore on oath was that the 
