174 



NA TURE 



\Feb. 20, 1890 



Bunsen lamp without any alteration in weight being noticeable. 

 The products of combination are generally gaseous mixtures of 

 CF4 and probably C2F4, When the most readily attacked varieties 

 of carbon are employed, and only in small quantities so as to avoid 

 excess, the gas is almost pure CF4. Carbon tetrafluoride is a 

 colourless gas, which liquefies under a pressure of five atmo- 

 spheres at 10° C. It is completely absorbed and decomposed 

 by an alcoholic solution of potash with production of potassium 

 fluoride and carbonate. On decomposing the latter salt with an 

 acid the volume of carbon dioxide liberated is the same as that 

 of the carbon tetrafluoride used. CF4 is slightly soluble in 

 water, more readily in carbon tetrachloride, alcohol, or benzene. 

 Determinations of its density gave numbers which agreed with 

 the formula CF4. If excess of carbon is heated to redness in a 

 platinum tube, and fluorine allowed to slowly stream through, 

 another gas is obtained on collecting over water which is not 

 capable of being absorbed by alcoholic potash. This gas 

 liquefies at 10° under a pressure of 19-20 atmospheres. M. 

 Moissan does not seem to have yet determined its composition, 

 but it appears likely to be the C^Fj described in the second com- 

 munication by M. Chabrie, M. Moissan also states that CF4 

 may likewise be prepared by passing vapour of carbon tetra- 

 chloride over silver fluoride heated to a temperature of 300° C. 

 in a glass or metal tube. M. Chabrie shows that both CF4 and 

 C2F4 may be obtained by heating the corresponding chlorides of 

 carbon with silver fluoride in a sealed tube to 220° C. In an 

 actual experiment 5'i grams of AgF were heated with i'55 

 grams of CCI4 for two hours, at the end of which time the tube, 

 which itself was but little attacked, was opened, and an 

 almost theoretical yield of CF4 obtained ; the gas was totally 

 absorbed by alcoholic potash in accordance with the equation 

 CF4 -f 6KOH = K2CO3 + 4KF -t- 3H2O. When C2CI4 was 

 used instead of CCI4, a gas whose density corresponded to the 

 formula C2F4 was obtained. The experimental density was 3"43 ; 

 the calculated value for C2F4 is 3 "46. The spectra of the two 

 fluorides, according to M. Moissan, exhibit the lines of fluorine 

 very clearly, together with several broad bands, resembling the 

 flutings of carbon. 



OUR ASTRONOMICAL COLUMN. 



Objects for the Spectroscope. 



Sidereal Time at Greenwich at 10 p.m. on February 20 = 

 8h. 3m. 7s. 



Remarks. 



(i) " Planetery nebula ; pretty bright, pretty small ; extremely 

 little elongated." The spectrum has not yet been recorded. 



(2) A star of Group II. Duner states that the bands are very 

 wide and dark in the red, but weaker in the green and blue. He 

 does not, however, state what bands are present. Observations 

 similar to those already suggested for other stars of the group 

 are required. 



(3) This is stated to have a fine spectrum of the solar type by 

 Vogel. The usual differential observations are required. 



(4) A star of Group IV, (Vogel). Usual observations 

 required. 



(5) This star has a very feeble spectrum of the Group VI. 

 type, which has not yet been fully described. 



(6) Although Cygnus is not now in the most convenient posi- 



tion for observations, it may still be observed soon after sunset. 

 The variable, S Cygni, has not yet had its spectrum recorded, 

 and the approaching maximum (February 28) may therefore be 

 taken advantage of. Gore states the period as 323 days, and 

 the range as from 8'8-io'i at maximum to <I3 at minimum. 

 If it has a banded spectrum, as may be expected from the 

 colour, the type of spectrum will probably not be difficult to 

 determine, notwithstanding the faintness of the star. 



A. Fowler. 



Progress of Astronomy in 1886. — An account of the 

 progress of astronomy in the year 1886, by Prof. Winlock, has 

 been issued from the Smithsonian Institution. Although the 

 record is primarily intended to serve as a series of notes for 

 those who have not access to a large astronomical library, the 

 bibliography will be found useful to the professional astronomer 

 as a reference list of technical papers. A considerable amount 

 of useful information is given in this extract from the Smith- 

 sonian Report for 1886-87, the section devoted to reports of 

 Observatories being very complete. A subject-index to the 

 review has been effected by inserting the necessary page refer- 

 ences to the bibliography. 



The Maximum Light-Intensity of the Solar Spec- 

 trum. — We have received from Dr. Mengarini his paper on 

 the above subject ( Untersttchungen ztir Nattirlehre des Menschen 

 und dcr Thiere, xiv. Band, 2 Heft). After reviewing the pre- 

 vious work that has been done on the varying intensity of differ- 

 ent parts of the spectrum, the author describes the three methods 

 he used in his researches. The observations led him to conclude 

 that the maximum of light-intensity is subject to variability in 

 position from day to day and hour to hour, just as the maxima 

 of thermal and chemical effects of the spectrum, although the 

 sky be clear and the atmosphere steady. Using a prismatic 

 spectrum, it was found that the maximum light-intensity fluctu- 

 ated between about A 564 and D, and, generally speaking, was 

 more pronounced in the morning than in the afternoon. Some 

 observations made at Rome in July 1881, on clear or slightly 

 clouded days, showed that the maximum shifted from A 564*1 

 to 584-3. 



Spectrum of Borelly's Comet, g 1889. — Mr. Back- 

 house, in a letter to the Observatory, notes that he ob- 

 served the spectrum of this comet with a Browning miniature 

 spectroscope on the 15th and 19th ultimo. The three CO 

 bands were very vividly seen, but no other line ; on the former 

 date there was a very faint continuous spectrum, but on the 

 latter only a suspicion of such. 



Spectra of 5 and ^l Centauri. — Prof. Pickering, in a 

 communication to Astronomischc Nachrichten, No. 2951, records 

 that an examination of the photographs of stellar spectra taken 

 by Mr. S. J. Baily at the Harvard Observatory station, near 

 Closica, Peru, shows that the F line due to hydrogen is bright 

 in the spectra of the stars S and /it Centauri. 



On the Star System \ Scorpii. — Some elaborate re- 

 searches into the orbits of the components of this system were 

 given by Dr. Schorr in an inaugural dissertation at Munich Uni- 

 versity last year. All available measures of position-angle 

 and distance have been brought together and compared 

 with those derivable from the new elements found, making the 

 computation of great value. 



GEOGR4PHICAL NOTES. 



On Tuesday, Dr. Nansen lectured in Christiania on his plan 

 for a North Pole Expedition. He advocates the employment of 

 a ship built with a special view to strength, having its sides con- 

 structed at such an angle that, instead of being crushed by the 

 ice, the vessel would be raised by it. The Expedition, he 

 thinks, should advance through the Behring Straits, where the 

 vessel would be carried northward by a favourable current. A t 

 the New Siberian Island the vessel would enter the ice-floes. Il 

 would then *' proceed towards the North Pole, in which direc- 

 tion the current would probably carry it." 



The Colonies and India gives the last news from Cooktown 

 relating to Sir William Macgregor's explorations in New Guinea. 

 His project was to ascend the Fly River on another voyage of 

 discovery. It seems that Sir William and his party, in a steam 

 launch, dropped anchor in the river on December 14. The 



