190 GEEAT CARE AND SKILL 



our most fertile soils. Half a pound in 100, makes 

 but a small figure when we come to give the compo- 

 sition of a single pound; it is only five-thousandths, 

 iXi%J5) of ^ pound. Now 1 lb. is a far larger quantity of 

 material than can be used with safety for an accurate 

 analysis. The instruments employed, and the various 

 methods of operation adopted, are such as, in nearly 

 all cases, to forbid the use of a large bulk or weight 

 of the substance to be examined. Consequently only a 

 small fraction of a pound is worked upon, and from 

 this all of the bodies present are to be separated, even 

 down to small parts of a single grain. 



It becomes at once obvious, that very great care, 

 very good apparatus, and no small portion of skill, are 

 requisite to an analytical chemist in the determination 

 of these minute quantities. If any of the chemicals 

 used in the analysis are impure, the impurities of 

 course have an influence upon the result: hence the 

 chemist must know the properties of many other bo- 

 dies beside those upon which he is at work, in order 

 to be sure that he is not adding something which 

 will prove injurious to the accuracy of his results. 



There is still another, among many points that 

 might be noticed in this connection. The processes 

 necessary for the determination of potash, soda, and 

 phosphoric acid, when all are present and in combi- 

 nation with other bodies, are in the last degree com- 

 plicated and difficult. Many ways of determining 

 them are described in books; some of these are alto- 

 gether faulty, and all require much skill and know- 

 ledge on the part of the operator, that he may avoid 

 serious errors. These bodies, it will be remembered, 

 are among the most important that soils contain, be- 

 cause they are most likely to be exhausted by crop- 

 ping. A comparatively inexperienced or uninstructed 

 person, may determine iron, alumina, or silica, those 



