188 EVILS RESULTING 



necessary, not only with the substances themselves in 

 their almost endless relations and changes; but with 

 great numbers of other substances from which they 

 must be distinguished, and with which they are likely 

 to be confounded by an inexperienced person. 



We can only determine quantities by means of cer 

 tain chemical processes : most of these depend on the 

 addition of other bodies, to a solution in which 

 are dissolved those that we wish to separate. Sup 

 pose now these bodies which are thus added to be im 

 pure : obviously the whole result will be erroneous; 

 the chemist then, must know how to distinguish with 

 certainty between pure and impure substances, and to 

 tell what the impurities are. 



When he knows all of these things, there are still 

 a great number of minor but very important points, 

 that require attention. He must use absolutely pure 

 water, must filter his liquids through paper that has 

 very little ash, and must weigh everything upon a 

 balance that is sensitive to at least the tenth of a 

 grain. 



I might go on and mention other requisites to a 

 good analysis, but those already noted are sufficient 

 to show, that great care, skill, and experience, are 

 absolutely essential in this business; that uninstructed 

 persons must constantly be making mistakes of the 

 most flagrant description. The worst difficulty of all 

 is, that in many cases, not having even knowledge 

 enough to know when they have gone astray, they 

 actually rely upon their own work as trustworthy, and 

 lead others to do so too. 



Results produced by such proficients are unhappily 

 too common, and are always productive of harm 

 wherever they go. The farmer, who knows little or 

 nothing of even chemical names, perhaps is not com 

 petent to judge of a good analysis; he can not tell the 

 difference between a pretender to scientific know- 



