436 MODERN CHEMISTRY. 



expressed, form the basis and test of experiment ; and exact 

 cognizance must be had of every quantity gained or lost by 

 the substance operated upon. No conclusions are deemed 

 perfectly valid unless so substantiated. This higher principle 

 of research mainly due in its origin to Lavoisier has 

 given such perfection to chemical theory as applied to analysis, 

 that the chemist can often foretell results before entering 

 his laboratory ; and experiment comes rather as fixing and 

 completing the deductions from general laws than as dis- 

 closing facts previously unknown. In our own country 

 Dr. Wollaston contributed perhaps more than any other to 

 the exactness of experimental enquiry. If we name Berzelius, 

 Mitscherlich, Liebig, and Dumas at the same time, we do so 

 with hesitation, lest we should seem to disparage other great 

 Continental chemists whose labours have tended to this per- 

 fection of the science they profess, 



While referring to the increased exactness of all chemical 

 knowledge, we must give the statement a more particular 

 application to whatever concerns the influence of small quan- 

 tities in composition. We have already adverted to the 

 frequent case of an ingredient existing in very minute pro- 

 portion, yet conveying important or even essential chemical 

 properties to the compound of which it forms a part ; or 

 what is an analogous case, to the effect of a slight change in 

 the proportions of one ingredient in altering the qualities of 

 the whole. Modern chemistry is replete with instances of 

 such facts ; the proper estimate of which is indispensable to 

 the understanding of the science. It has belonged to the re- 

 finements of recent analysis to detect, and assign their proper 

 value to, these more minute ingredients ; while at the same 

 time discovering many new and rare elements, and indicating 

 purposes which they fulfill in. the economy of nature, even by 

 virtue of their diffusion and minuteness. In organic chemistry, 

 whether of animal or vegetable life, we find this admirably 



