iv PREFACE TO THE FIFTH EDITION. 



tion of beginners in chemistry. All our classifications of either natural 

 objects or phenomena are imperfect, because Nature does not draw those 

 distinct lines of demarcation which we adopt as necessary for our studies. 

 The most simple and natural classification is therefore always to be pre- 

 ferred, even if, as in the above case, the student might derive from it the 

 impression that matter was thus separated into distinct groups. 



Of elements, those only are considered which have either intrinsically 

 or in combination a practical interest, or which take an active part in the 

 various chemical changes in nature. 



For the special benefit of pharmaceutical and medical students all 

 chemicals mentioned in the last revision of the United States Pharma- 

 copoeia are included, and when of sufficient interest they are fully 

 considered. 



The fifth part is devoted to analytical Chemistry and will serve the 

 student as a guide in his laboratory work. Qualitative methods are 

 chiefly considered, but a chapter is added giving all official methods for 

 volumetric determinations. 



The sixth part treats of organic chemistry. Though it is impossible to 

 include within the limits of this text-book an extended consideration of a 

 branch of chemical science so highly developed, yet it is believed that an 

 intelligent study of this part will familiarize the student with carbon 

 compounds sufficiently to give him a clear understanding of their general 

 character, and a knowledge of the bodies which are most important in 

 medical science. 



The seventh and last part, giving some of the principal facts of physio- 

 logical chemistry, was prepared for the benefit of the medical student in 

 particular. Much new matter has again been added to these chapters, 

 and special care has been taken to mention the most modern methods f jr 

 chemical examination in clinical diagnosis. 



As an aid to laboratory work a number of experiments have been 

 added which may readily be performed by students with a comparatively 

 small outfit of chemical apparatus. 



The decimal system has been strictly adhered to in ail weights and 

 measures ; degrees of temperature are expressed in the same system, the 

 corresponding degrees of Fahrenheit being also mentioned. 



Many changes have been made on the plates showing the variously 

 shaded colors of a number of substances and the nature of their reactions. 

 There has also been added a new plate illustrating the chemical behavior 

 of a number of the more important benzene derivatives. 



W. 8. 



BALTIMORE, January, 1895. 



