40 JOURNAL OF THE [April, 



tained in any square or number of squares, and by this means 

 to arrive at the average proportions of each kind of material con- 

 tained in the mass. 



A glance through the microscope at some of these paper com- 

 positions will, I think, satisfy you that, even after making many 

 measurements and taking the average of them, the final determi- 

 nation will be far from correct, on account of the thoroughly 

 intermingled condition of the various substances; the differences 

 in the dimensions of the divers kinds and shapes of the fibres; the 

 broken portions of many of these; as well as the impossibility of 

 discriminating between the ingredients in their disintegrated state. 

 For the reasons given I have not, up to this time, attempted a 

 quantitative determination in mixed or adulterated papers. For 

 similar reasons no fixed rule can be laid down for optically 

 separating the constituents in the finer papers, except by long 

 and diligent practice with the microscope, thereby training the 

 observer's eye and mind for the discrimination necessary in de- 

 tecting such matter as one finally becomes familiar with by certain 

 details he has previously recognized, and by comparison with the 

 elements which form the component parts of the usual admixtures 

 or adulterations named in the subject of this evening. 



I am thankful to Prof. Stillman for bringing this matter to my 

 attention originally; for the valuable aid he has given me in his 

 chemical preparations; for collecting examples of paper stock; 

 and in pointing out much of the bibliography bearing upon this 

 class of investigation. You are also indebted to him for the 

 color reactions which he has so well shown, by means of the 

 numerous examples of ])ulps and paper treated by him which 

 I have laid before you, and which I will briefly explain when I 

 apply some of these reagents to show you their rapid action on 

 some papers.^ 



We are under obligations to Dr. E. G. Love for the photo- 

 micrographic illustrations of many of the slides upon the tables, 

 which enable us to more readily conceive the appearances of the 



' On account of the chemical investigations by Prof. T. B. Stillman, now in progress 

 and relating to papers and their constituents, I do not mention at this time ary ol the 

 other chemical reagents shown here, but hope that he will in the near future give for 

 publication, in a chemical or other technical journal, a more complete means of chem cat 

 identilication than has hitherto been known. 



