paratively few cases, be executed satisfactorily, and a qtialitative 

 result has mostly to satisfy the operator. 



4. To fathom the chemical constitution of a mineral, one or a 

 few grams weight are almost always quite sufficient. 



On the contrary, to ascertain qualitatively, and even supei*- 

 ficially, all the constituents of a plant, at least a hundred times 

 more material is required, but which, if a profound study of the 

 single constituents is aimed at, has still to be increased ten or 

 even a hundred fold. 



5. It belongs to the I'arest cases, generally only occurring after 

 intervals of years, to meet, in the analysis of a mineral, with a 

 constituent previously quite unknown, the discovery of which means 

 at the same time that of a new element. 



In a j)hyto-chemic analysis, on the other hand, it is not un- 

 common to obtain constituents unkno^v^i before. It therefore 

 offers still a very fertile field for discoveries, though it ought not 

 to be overlooked, that the accurate decision in regard to the 

 correctness of such a discovery is mostly no easy task, because it 

 depends on the purity and quantity of the material, which is not 

 ahvays so obtainable. 



6. During the analysis of minerals a decomposition of the con- 

 stituents, as regards their elements, need of course not be appie- 

 hended; the occurring changes consist only in the absorption or 

 liberation of oxygen, sulphur, a few other elements — and volatile 

 acids; the relations of these to the object of examination, whether 

 they are constituents of the same or not, are already answered 

 satisfactorily by other operations of the analysis. 



The phyto-chemic analysis, on the contrary, is never safe against 

 irreti'ievable losses, and this is the more impeding, because those 

 constituents are mostly lost, on the determination of which the 

 success of the whole operation mainly depends. The causes of 

 such losses are either the easy decomposibility, or the volatilit}-, 

 or the solubility of many organic substances. To avoid such 

 losses must be the incessant endeavour of the analytic ojierator, 

 if he will not run the risk of losing the fruits of perhaps months 

 of toil. 



