Intelligence and Miscellaneous Articles. 161 



In page 68 of my book, with a view to a brief explanation for the 

 Tyro in chemistry of what is meant by a binatomic body, a brief 

 statement is made which is certainly not correct. In point of fact 

 the reaction described between Dutch liquor and water has not been 

 observed ; but, assuming it to take place, we have a simple expla- 

 nation of what is meant by a triatomic organic radical ; and what 

 was in my mind when writing this passage was, to speak hypotheti- 

 cally of the reaction, though this I find has not been done. I can 

 assure the reviewer that I was not ignorant of the series of processes 

 by which biniodide of ethylene is convertible into glycol, and the 

 latter into the biniodide of ethylene ; but the description of these 

 would have been quite unintelligible to the junior student, and, at 

 the same time, altogether unsuited to my introductory chapter. 



In pages 561 r and 562 I give an explanation of Liebig' swell-known 

 method for the estimation of hydrocyanic acid, in relation to which 

 the reviewer has the following passage : — " It is difficult to suppose 

 that the writer of this passage has ever performed the operation he 

 professes to describe, otherwise he could hardly have failed to notice 

 that in reality it is the white cyanide of silver, and not the brown- 

 grey oxide which appears as a permanent precipitate." In reply to 

 this commentary, I beg to state that the inference suggested would 

 be quite erroneous. The experiment in question is one which, as a 

 teacher of chemistry, I am obliged repeatedly to perform ; and I may 

 add that, in doing so, I have not failed to observe the white precipi- 

 tate of which he makes mention. This, however, or rather the por- 

 tion of it which first falls, is not cyanide, as alleged in the review, but 

 chloride of silver, arising from the alkaline chlorides invariably pre- 

 sent in the ordinary solutions of soda and potash. If the solution 

 of caustic potash was absolutely pure, it appeared to me a probable 

 conclusion that the precipitate would be oxide of silver, and hence 

 it has been described as such ; but I am now by actual experiment 

 aware that this is not the case, and that, after the whole of the 

 hydrocyanic acid has been converted into the soluble double cyanide, 

 it may be thrown down as insoluble cyanide of silver by adding just 

 as many measures (chloride being supposed absent) of the volume- 

 tric solution of nitrate of silver as have been already employed. 

 The ignorance on this latter point, which I freely avow, the reviewer 

 no doubt considers as quite unpardonable ; but I am not without 

 hope that the candid critic will feel himself at liberty to pronounce 

 a more lenient judgment, the more especially as a knowledge of 

 the nature of the permanent precipitate which appears in this volu- 

 metric process is not necessary with a view to the accuracy of the 

 experiment. Chemical reactions cannot be always predicted with 

 certainty ; and the charge against me simply amounts to this, that, 

 not having made the trial, I did not know that the cyanide of potas- 

 sium of the double cyanide would be precipitated by nitrate of silver. 



The next charge preferred against me is one of rather a paradoxical 

 nature, being actually that I have stated the compounds of nitrogen 

 with hydrogen to be three in number, viz. amidogen, ammonia, and 

 ammonium, — of which he says that " a more misleading statement 

 could not easily be put before the student." As a further illustra- 

 Phil. Mag. S, 4. Vol. 28. No. 187. Aug. 1864. M 



