SCIENCE-GOSSIP. 



259 



paratively recent date, and both it and esparto are 

 confined mainly to the less expensive classes of 

 printings and writings. Of all these fibres only 

 one has a large central cavity combined with thin 

 :side-walls, i.e. cotton. All the papers examined 

 by me contain cotton fibres, and I have found no 

 example of a dendrite in any other fibre, so am 

 inclined to question its possibility, on account of 

 the small central canal. 



I hope to be able, at a not distant date, to con- 

 tribute to this journal a paper dealing with the 

 microscopic examination of fibres, more especially 

 those used in paper-making. By means of these 

 notes the readers can themselves verify these state- 

 ments, though the identification of certain fibres, 

 more especially after being made into paper, is a 

 matter requiring - much practice. 



With regard to the metallic origin of these spots, 



3 H 2 0, and into cupric ammonia nitrate, Cu(NO g ) 2 , 



4 NH 3 ; its precipitation as Cu(HO) 2 , and subse- 

 quent characteristic solution in ammonia; and its 

 precipitation also with potassium ferrocyanide 

 as Cu 2 FeCy„, further verified with acetic acid. 

 The process in this case requires no higher power 

 than the use of an objective of an inch nominal 

 focus. Copper is usually stated as being on- 

 oxidisable at ordinary temperatures, but this is 

 manifestly not correct, as it is certainly oxidisable 

 in air containing any moisture, but only with 

 difficulty and after the lapse of considerable time. 

 It is possible that the use of bleaching-powder 

 and other chemicals used in the process of 

 manufacture may aid the oxidisation. I have 

 no hesitation, therefore, in saying that these den- 

 dritic spots may now be definitely stated to be 

 formed by the slow oxidisation of a minute spot of 



'■-■- t-sS^" 



Dendritic Spots in Paper. 

 (Highly magnified and photographed bit F. Shillington Scales, F.R.M.S:) 



I was inclined to credit the theory of deposition of 

 a minute particle of copper, because brass enters 

 largely into the machinery used in paper-making, 

 notably, so far as our present interests are con- 

 cerned, in the broad sheet of endless wire gauze 

 on which machine-made paper is felted, and in the 

 brass " beater plates," by means of which the finer 

 qualities of papers are reduced to pulp instead of 

 by the usual steel plates. Small particles of brass 

 and other metals, such as brass hooks and eyes, 

 are also a frequent trouble in rag-made papers. 



It appeared that this was a typical case for 

 micro-chemical analysis, in which the writer has 

 long been interested, and small though the nuclei 

 of these spots are, I was able to obtain unmistake- 

 able reactions proving that the nuclei were indeed 

 nothing but minute particles of copper. For those 

 of our readers interested in such matters I may 

 mention that the analysis included the conversion 

 ■of the nuclear spot into cupric nitrate, Cu(N0 3 ) 2 



metallic copper, deposited in the process of paper 

 manufacture, into the black cupric oxide (CuO). 

 The slowness of the oxidisation is evidenced by the 

 length of time required for the formation of these 

 dendrites, as stated by Mr. Tait. Their absence 

 from modern papers is due partly to this cause, 

 and partly, unless this theory requires modifica- 

 tion, to the fact that the comparatively solid fibres 

 of wood-pulp and esparto used in modem paper- 

 making do not lend themselves readily to the 

 branching out of these formations. We must 

 therefore look in rag-made papers of mature age 

 for them, especially in ledgers and account hooks, 

 to which, in this age of cheapness, rag-papers are 

 now chiefly confined. That such papers are gene- 

 rally made with a more or less pronounced blue 

 tint is the only explanation 1 can give of the fact 

 that five-sixths of the dendritic spots submitted to 

 me were found in blue-tinted papers. 

 Sunderland, January 1901. 



K 2 



