138 



NA TURE 



{Dec. 12, 1889 



-structure of thin plates, or one of fine lines. There are two 

 papers on leaves from the cutting of the Ship Canal, one giving 

 a general description, and the other, by Dr. Schunck, F. R. S. 

 showing that the green colouring-matter, which has proved to 

 be so permanent, is due to a modified form of chloroph3'll ; spec- 

 troscopic examination of the colouring-matter showed it to be 

 identical with that produced by the action of dilute hydrochloric 

 acid on ordinary chlorophyll. 



The Middlesex Natural History and Science Society has 

 issued a volume containing its Transactions during the session 

 1888-89. The volume opens with an interesting Presidential 

 address by Prof. Flower, on the Natural History Museum, 

 •Cromwell Road, and some recent additions thereto. Mr. E. 

 M. Nelson has an illustrated paper on diatom structure ; and 

 Mr. J. A. Brown contributes a paper, also illustrated, on work- 

 ing sites and inhabited land surfaces of the Palaeolithic period 

 in the Thames Valley. 



The fourth volume of " Blackie's Modern Cyclopaedia " has 

 ■been issued. It begins with the word "fire" and ends with 

 ^' Ilorin." The work, as we have said on former occasions, is 

 admirably edited by Dr. C. Annandale. The articles are 

 necessarily brief ; but, so far as we have been able to test them, 

 they are clear and accurate. There is no falling off in the 

 present volume. 



Messrs. Ward, Lock, and Co., have added to their 

 "" Minerva Library of Famous Books" a reprint of Dr. A. R. 

 Wallace's fascinating "Narrative of Travels on the Amazon and 

 Rio Negro." A biographical sketch of the author is contributed 

 by Mr. G. T. Bettany, the editor of the series ; and the volume 

 includes a portrait of Dr. Wallace, a map, and full-page 

 illustrations. 



Hazell's Annual for, 1890- — the fifth issue — has been pub- 

 lished. It is edited by Mr. E. D. Price. An immense quantity 

 of information, alphabetically arranged, has been packed into 

 this useful volume. Many articles which the editor describes as 

 ^' new and important " have been inserted in the present issue. 



A Science Club has been formed among the students of the 

 University of St. Andrews for the purpose of developing 

 the interest already taken in scientific pursuits. Prof. W. C. 

 IMcTntosh, F.R. S., has been elected Hon. President for the 

 session 1889-90. 



Another important paper by M. Henri Moissan upon the 

 'perfected mode of preparation and upon the density of fluorine, 

 is contributed to the current number of the Coniptes remhis. 

 Since the appearance of his paper of two years ago, M. Moissan 

 has employed an electrolysis apparatus of much larger size, and 

 has added to it an accessory apparatus by means of which the 

 gas may be obtained quite free from vapour of hydrofluoric acid, 

 Avhich, as described in Nature last week, is the cause of the 

 •destructive action upon platinum. The platinum U't^^^c of the 

 new apparatus has a capacity of 160 c.c, and contains during 

 -i(he electrolysis ico c.c. of hydrofluoric acid. The exit tube at 

 the positive side, from which the fluorine is liberated, is con- 

 tinued into a small platinum spiral condenser immersed in a 

 bath of methyl chloride at - 50° C, where all but the last trace 

 ■of hydrofluoric acid is retained. From this the gas is led through 

 «wo platinum tubes filled with fragments of sodium fluoride, a 

 salt which combines with hydrofluoric acid with great energy, 

 forming hydrogen sodium fluoride. By these means the fluorine 

 is obtained perfectly pure, and is quite invisible in dry air, no 

 trace of fuming being apparent, as is the case before purifica- 

 tion. In order to determine the density of the gas, a couple of 

 ingeniously constructed platinum flasks have been employed. 

 Each of these flasks is closed by a cylindrical stopper also of 

 platinum ; to the side of the neck a side tube is attached on a 



level with the centre of the stopper. Through the stopper an 

 aperture is bored in such a manner that, when the stopper is 

 rotated into a certain position, connection is established between 

 the interior of the flask and the side tube. A vertical tube also 

 passes through the stopper and penetrates to near the bottom 

 of the flask ; this tube is also closed at its upper end 

 by means of a platinum stopper. The stoppers are finely 

 polished and adjusted with great care. Each flask weighs about 

 70 grams and has a capacity of about 100 c.c. In the density 

 determinations the two flasks were counterpoised on the two 

 pans of the balance. One of them was then filled with pure dry 

 nitrogen gas, which was subsequently displaced by the pure 

 fluorine, the electrolysis apparatus being connected with the 

 upper end of the vertical tube of the density flask by means of 

 flexible platinum tubing. The fluorine was allowed to pass 

 through the apparatus for five minutes after cold silicon was 

 readily ignited by the gas issuing from the side exit tube. The 

 stopper of the flask was then rotated through half a revolution, 

 so as to completely shut off the exit tube, and the stopper of the 

 vertical tube replaced. The flask was again weighed against the 

 other flask containing air, and the difference of weight noted. 

 The amount of residual nitrogen was estimated by opening the 

 stopper of ithe vertical tube under water, when the fluorine 

 instantly decomposed an equivalent of water, liberating oxygen 

 and forming hydrofluoric acid. The mixture of oxygen and the 

 residual nitrogen was then collected, and the oxygen absorbed by 

 pyrogallic acid and potash. Three determinations yielded, for 

 the density of fluorine compared with that of hydrogen, 18 '2?, 

 1 8 "26, and 18 "33. These values appear to indicate that the 

 number 19, usually taken as representing the atomic weight of 

 fluorine, is slightly too high, and this view is confirmed by the 

 low numbers obtained in former determinations of the density of 

 phosphorus trifluoride. 



The additions to the Zoological Society's Gardens during the 

 past week include a Malayan Bear ( Ursus malayaiins 9 ) from 

 Malacca, a Gold Pheasant {Thaitmalca picta ?) from China, 

 presented by Captain Bason ; a Common Squirrel {Sciurtis 

 vulgaris), British, presented by Mr. W. Aubrey Chandler ; a 

 Mexican Deer [Cariactcs mcxicamts i ) from Peru, a Grey- 

 breasted Parrakeet {Bolborhynclms vionachus) from Monte 

 Video, deposited ; an American Bison (Bison aincricanus S 

 born in the Gardens. 



OUR ASTRONOMICAL COLUMN. 

 Objects for the Spectroscope. 

 Sidereal Time at Greenwich at 10 p.m., December 12 = 3h. 



27m. 93 



Remarks. 



(i) The General Catalogue description of this nebula is as 

 follows: — !!! Bright; very large, irregular figure. According 

 to Tempel, this is a variable nebula, and its spectrum, which 

 has not yet been recorded, will therefore have a special interest. 

 Continued observations may, very probably, give a clue to the 

 origin of the variability. 



(2) Duner classes this with stars of Group II., but states that 

 the spectrum is only feebly developed. Further observations 

 are necessary before it can be placed in position on the "tem- 



