ADDRESS. Ixxvii 



Thus it is of importance to notice that a singularly good training in the 

 accurate use of words is afforded by experimental Chemistry. Every one 

 who is about to enter on an inquiry, whether he be a first-year's student 

 who wants to find the constituents of a common salt, or whether he be the 

 most skilled and experienced of Chemists, seeks beforehand to get such in- 

 formation from the records of previous observations as may be most useful 

 for his purpose. This information he obtains through the medium of words ; 

 and any failure on his part to understand the precise meaning of the words 

 conveying the information requisite for his guidance is liable to lead him 

 astray. Those elementary exercises in analytical chemistry, in which brief 

 directions to the students alternate with their experiments and their reports 

 of experiments made and conclusions drawn, afford a singularly effective 

 training in the habit of attending accurately to the meaning of words used 

 by others, and of selecting words capable of conveying without ambiguity 

 the precise meaning intended. Any inaccuracy in the student's apprehension 

 of the directions given, or in the selection of words to describe his obser- 

 vations and conclusions, is at once detected, when the result to which he 

 ought to have arrived is known beforehand to the teacher. 



Accuracy of reasoning is no less effectively promoted by the work of ex- 

 perimental chemistry. It is no small facility to ns that the meaning of the 

 words which we use to denote properties of matter and operations can be 

 learnt by actual observation. Moreover each proposition comprised in che- 

 mical reasonings conveys some distinct statement susceptible of verification 

 by similar means ; and the validity of each conclusion can be tested, not only 

 by examining whether or not it follows of necessity from true premisses, 

 but also by subjecting it to the independent test of special experiment. 



Chemists have frequent occasion to employ arguments which indicate a 

 probability of some truth ; and the anticipations based upon them serve as 

 guides to experimental inquiry by suggesting crucial tests. But they distin- 

 guish most caroiuUy such hypotheses from demonstrated facts. 



Thus a pale green solution, stated to contain a pure metallic salt, is found 

 to possess some properties which belong to Salts of Iron. ]!^othing else pos- 

 sesses these properties except Salts of Nickel ; and they manifest a slight dif- 

 ference from Iron Salts in one of the properties observed. 



The analyst could not see any appearance of that peculiarity which distin- 

 guishes Nickel Salts ; so he concludes that he has probably got Iron in his 

 solution, brt almost certainly either Iron or Nickel. He then makes an ex- 

 periment which will, he knows, give an entirely different result with Iron 

 Salts and Nickel Salts ; and he gets very distinctly the result which indicates 

 Iron. 



Having found in the green liquid properties which the presence of Iron 

 could alone impart, he considers it highly probable that Iron is present. But 

 he does not stop there ; for, although the facts before him seem to admit of no 

 other interpretation, he knows that, from insufficient knowledge or attention, 

 mistakes are sometimes made in very simple matters. The analyst therefore 

 tries as many other experiments as are known to distinguish Iron Salts from 

 all others ; and if any one of these leads distinctly to a result at variance 

 with his provisional conclusion, he goes over the whole inquiry again, in 

 order to find where his mistake was. Such inquiries are practised largely by 

 students of chemistry, in order to fix in their minds, by frequent use, a know- 

 ledge of the fundamental properties of the common elements, in order to 

 learn by practice the art of making experiments, and, above all, in order to 

 acquire the habit of judging accurately of evidence in natural phenomena. 

 1873. n 



