MINUTE CHEMICAL ERRORS. 47 



This will be necessary because we must obtain some defi- 

 nite knowledge of the general chemical principles involved 

 in this experimental work in order that we may be able to 

 judge of the relative value of the different processes in use. 



This somewhat systematic view of the experimental 

 chemical work is also necessary because our general works on 

 chemistry give almost no information on this great subject 

 of the determination of atomic weights. 



This chemical work consists in the following operations: 

 I, selection or preparation of the material; II, performing 

 the chemical operation whereby the new material is 

 obtained; and III, determining the weight of these two 

 materials. 



It has already been stated, that the material must be 

 absolutely pure, the reaction or process complete and defi- 

 nite, and the weighings accurate. 



As only definite chemical compounds can undergo 

 definite chemical reactions, the starting material must be a 

 definite chemical compound or element, and the material 

 resulting from the reaction must also be of such chemical 

 nature. 



The necessity of obtaining the weight of these two mate- 

 rials greatly limits the choice of compounds that can be 

 used. Hygroscopic, efflorescent and otherwise readily 

 changeable materials must be excluded ; for they cannot be 

 handled and weighed with precision. 



It is very true that Stas and many of his imitators have 

 by ''skill" fancied to overcome these difficulties; but we 

 shall see, that these attempts were disastrous to chemistry. 



This is precisely what Berzelius warned against in his 

 Rule of 1814, printed p. 3. He means to say that the 

 completing of the reaction must depend upon the chemical 

 and physical properties of the materials themselves, and not 

 on the skill of the operating chemist. 



Unfortunately, our modern chemist tries to show off as a 

 sort of chemical acrobat or virtuoso, able to do something 

 very difficult, while Berzelius and his school skillfully used 

 the properties of matter with the sole aim of obtaining true 

 and reliable results. 



