186 
one atom of hydrogen being removed and entering into com- 
bination with one atom of chlorine or bromine, while another 
atom of the haloid element takes the place of the hydrogen 
removed. Thus, when chlorine acts upon marsh gas (methylic 
hydride) the products are hydrochloric acid and methylic 
chloride.* 
CH 4 + Cl 3 = HC1 + CH 3 C1 
and by the continued action of the chlorine the latter may 
be converted successively into CH 2 C1 3 and CHCL 3 , the last 
being the compound usually called chloroform. Behold the 
transformation ! 
59. Now, I trust I may be pardoned, in consideration of the 
importance of the result, for dwelling on these technicalities. 
Every one knows the soothing properties of chloroform , which 
exists nowhere in nature, but is the product of the chemist's 
art. Its twin sister, iodoform , was recently the means of 
saving a young life threatened by the result of a dreadful 
accident, and now full of hope and promise. 
60. The views which were attempted to be established, 
founded on the electrical relations of the elements, are dia- 
metrically opposed to what we now know of substitution.! 
Thus, atoms like chlorine, bromine, and iodine, are capable of 
replacing hydrogen atom for atom, and discharging functions 
similar to those of hydrogen in the primary compound. 
61. It must be remembered that we are speaking of bodies 
of almost inconceivable but not infinite minuteness ; not 
absolutely in contact, nor, on the other hand, capable of 
exercising these affinities at any distance that we can define. 
The action is what we call instantaneous, and frequently most 
marked and pleasing. I have often been delighted with 
beholding the production of colour from colourless liquids, 
and of crystallisation on the mixture of two uncrystallizable 
fluids. 
62. Such, then, is matter, or, as we may say, ponderable 
matter, — subjected to destiny, acting according to implanted 
impulses, and that with unerring certainty, — so that when we 
understand the nature of these impulses we can avail ourselves 
of our knowledge to alter to an unknown extent the resulting 
combinations ; producing continually things which have never 
existed from the beginning of time. 
* Watts’s Diet. Sub., vol. v. pp. 450, 452. 
t See further my Exam, of Tyndall’s Belfast Address, Trans, vol. x. p. 121, 
