Ixxviii REPORT — 1873. 



Such a student is often surprised at being told that it is not enough for him to 

 conduct his experiments to such a point that every conclusion except one is 

 contrary to the evidence before him- — that he must then try every confirma- 

 tory test which he can of the substance believed to be present, and ascertain 

 that the sample in his hands agrees, as far as ho can see, in all properties 

 Avith the known substance of which he believes it to be a specimen. 



Those who tread the path of original inquiry, and add to human know- 

 ledge by their experiments, are bound to practise this habit Avith the most 

 scrupulous fidelity and care, or many and grave would be the mistakes they 

 would make. 



Thus a Chemist thinks it probable that he might prepare some well-known 

 organic body of the aromatic family by a new process. He sets to work and 

 obtains a substance agreeing in appearance, in empirical composition, in 

 molecular weight, and in many other properties with the compound which 

 he had in view. He is, however, not satisfied that his product is a sample 

 of that compound until he has examined carefully whether it possesses all 

 the properties which are known to belong to the substance in question. And 

 many a time is his caution rewarded by the discovery of some distinct dif- 

 ference of melting-point, or of crystalline form, &c., which jn-ovcs that he 

 has made a new compound isomeric with the one which he expected to make. 

 It seemed probable, from the agreement of the two substances in many 

 particulars, that they might be found to agree in all, and might be considered 

 to be the same compound ; but complete proof of that conclusion consists iu 

 showing that the new substance agrees with all that we know of the old one. 



In the most vai'ious ways chemists seek to extend their knowledge of tbe 

 uniformity of nature ; and their reasonings by analogy from particulars to 

 particulars suggest the working hypotheses M'hich lead to new observations. 

 Before, however, proceeding to test the trutli of his hypothesis by experi- 

 ment, the chemist passes in review, as well as he can, all the general know- 

 ledge which has any bearing on it, in order to find agreement or disagree- 

 ment between his hypothesis and the ideas estabhshed by past experience. 

 Sometimes he sees that his hypothesis is at variance with some general law 

 in which he has full confidence, aud he throws it aside as disproved by that 

 law. On other occasions he finds that it follows of necessity from some 

 known law ; and he then proceeds to verify it by experiment, with a confident 

 anticipation of the result. In many cases the hypothesis does not present 

 sufficiently distinct agreement or disagreement with the ideas established by 

 previoiis investigations to justify either the rejection of it or a confident 

 belief in its truth; for it often happens that the results of experience of 

 similar phenomena are not embodied in a sufficiently definite or trustworthy 

 statement to have any other effect than that of giving probability or the 

 contrary to the hypothesis. 



Another habit of mind which is indispensable for success in experimental 

 chemistry, and which is taught by the practice of its various operations, is 

 that of truthfulness. 



The very object of all our endeavours is to get true ideas of the natural 

 processes of chemical action ; for in proportion as our ideas are true do they 

 give us the power of directing these in'ocesses. In fact our ideas are useful 

 only so far as they are true ; and he must indeed be blind to interest and to 

 duty who could wish to swerve from the path of truth. But if any one were 

 weak enough to make the attempt, he would find his way barred by innu- 

 merable obstacles. 



Every addition to our science is a matter of immediate interest and im- 



