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VIII.— 071 the Chemistry of Dendritic Growths in Paper. 

 By James Strachan, F.E.M.S. 



(Bead April 16, 1919.) 



1. Introduction. 



Eleven years ago, in a communication to this Society,* the present 

 writer reviewed the existent literature on the subject of dendritic 

 growths in paper, and, from his practical experience of paper and 

 paper-making, explained some features in the occurrence of these 

 growths hitherto puzzling to microscopists. 



This contribution confirmed the observations of Tait and Scales 

 concerning the composition of these growths, and attributed their 

 formation wholly to a process of oxidation acting upon a metallic 

 nucleus of bronze. A point, however, which was not explained 

 quite satisfactorily at that time was the manner in which the 

 insoluble copper compounds crept along the surface of the fibres. 

 All experiments performed subsequently with a view to production 

 of artificial dendritic growths by oxidation methods ended in 

 negative results. 



This led the writer to further experiments and consideration 

 of other theories. The publication of the above paper brought 

 forth the criticism and expression of opinion on the part of four 

 specialists in paper chemistry. Two of these confirmed the 

 oxidation theory from their own experience ; a third was doubtful, 

 and remarked the occurrence of similar growths in waterproofed 

 fabrics ; while the fourth stated definitely that all dendrites in 

 paper examined by him contained sulphide of copper. 



2. Eesults of Further Investigations. 



Subsequent investigations carried out from time to time during 

 the past ten years, in which many hundreds of specimens were 

 examined, led the writer to adopt the following explanation of 

 these interesting growths, which is undoubtedly the correct one. 



We commence with a nucleus of bronze or brass imbedded in 

 a felted sheet of cellulose fibres, containing other substances com- 

 prising paper. The following factors must be considered : — 



(a) Presence of Moisture. — The hygroscopic moisture of the 

 cellulose may amount to 15 p.c. in a moist atmosphere. 



* Journ. E. Micr, Soc, 1908, pp. 5M-50 (pi, xiii.). 



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