XIV PREFACE. 



to avail themselves of it in order to bring their processes 

 to the requisite degree of precision. 



Nor will the atomic theory prove less important to 

 apothecaries and druggists, and preparers of medicines. 

 It will point out the exact proportions of every substance 

 to be used, and will enable them to attain their object in 

 the most simple and direct manner, without any unprofit- 

 able waste by employing more or less of the different 

 substances than is just requisite for the intended object. 

 To them, and indeed to all medical men and medical 

 students, the knowledge of the atomic theory is of the 

 utmost consequence, and they will find the present publi- 

 cation of no little service to them. The tables contained 

 in this work ought to occupy a place in every laboratory, 

 and to lie upon the shop of every druggist, that he may 

 have it in his power to have recourse to them to regulate 

 all his processes. 



The work which I now present to the public contains 

 the result of many thousand experiments, conducted with 

 as much care and precision as it was in my power to 

 employ. They have occupied the whole of my time 

 (except what was necessarily devoted to the duties of my 

 situation,) for the last five years. All those experiments 

 which I considered as fundamental, were repeated so 

 often, and varied in so many ways, that I repose the most 

 perfect confidence in their accuracy. I may therefore, 



