350 



NA TURE 



\_Feb. 13, 1890 



On inhaling, one perceives no odour so long as this cylinder does 

 not project beyond the inner tube ; but the further it is pushed 

 out, the larger is the scented surface presented to the entering 

 air, and the stronger the odour perceived. The author studies 

 mixture of odours by applying a cylinder saturated with a 

 scented body to the end of the olfactometer, and varying the 

 length of the two odoriferous substances. But he considers a 

 double olfactometer better (one tube for each nostril). "With 

 this, one may easily experience how one odour will overwhelm 

 another ; rubber, e.g., causing the smells of paraffin, wax, andtolu 

 to disappear. Even with very strong excitants, there is never a 

 mingling of sensations. Either the one or the other odour is 

 perceived, till by cai-eful equilibration of the two, no sensory 

 effect at all is perceived. Sensibility is quite eliminated. 



The Verein Itir Erdkunde, of Halle, is arranging for a hydro- 

 graphical and zoological investigation of the Lake of Ploen, in 

 Holstein. 



Vienna and Berlin will shortly be connected by telephone. 



A PRETTY and convenient celluloid paper knife is being sent 

 by Messrs. Woodhouse and Rawson United, Limited, to their 

 clients. No one who uses it can doubt that celluloid may for 

 some purposes be a very good substitute for ivory. 



Messrs. William Wesley and Son have issued No. 99 of 

 their " Natural History and Scientific Book Circular." It 

 consists of a list of works in astronomy, mathematics, and 

 physics. 



A paper upon phosphorus trifluoride is contributed by M. 

 Moissan to the February number of the Annales de Chimie et de 

 Physique. In a previous communication it was shown that this 

 interesting gas could be obtained either by heating a mixture of 

 lead fluoride and copper phosphide, or by the action of arsenic 

 trifluoride upon phosphorus trichloride. Since that time it has 

 been found that a regular and more rapid evolution of phosphorus 

 trifluoride occurs when a mixture of zinc fluoride and phosphorus 

 tribromide is gently warmed, and this appears to be by far 

 the most convenient way of obtaining the gas in quantity. Zinc 

 fluoride reacts much more rapidly than lead fluoride, and is best 

 prepared by the action of pure hydrofluoric acid upon zinc car- 

 bonate. The insoluble fluoride thus obtained is washed with 

 distilled water and dried at 200° C. It is important not to raise 

 the temperature beyond this point, as further heating renders it 

 much less easily attacked by phosphorus tribromide. The dry 

 zinc fluoride is then placed in a brass tube closed at one end and 

 fitted at the other with a double bored ordinary cork, well 

 paraffined, and through which pass two tubes, one a delivery 

 tube of lead, and the other a kind of dropping funnel, from which 

 the tribromide of phosphorus is allowed to slowly fall upon the 

 gently warmed fluoride of zinc. As soon as the temperature of 

 the latter has begun to rise, the action becomes very energetic, 

 and in a few moments several litres of the gas may be collected. 

 In order to free the phosphorus trifluoride from admixed vapour 

 of phosphorus tribromide, it is quite sufficient to allow it to 

 bubble through a little water contained in a small wash bottle, 

 after which it may be dried by passing through tubes containing 

 pumice, which has been boiled in strong oil of vitriol, and 

 heated until only the minimum quantity of sulphuric acid remains 

 adhering to it, inasmuch as the strong acid absorbs a notable 

 quantity of phosphorus trifluoride. The gas is finally collected 

 over mercury. The reaction occurring during the preparation 

 is stated to be as follows : — 



SZnF^ -f 2PBr3 = 2PF3 -f sZnBrg. 

 Gaseous trifluoride of phosphorus as thus prepared possesses a 

 very sharp odour, but does not fume in the air. It is very 

 slowly absorbed by water, but is decomposed immediately by 



solutions of chromic acid or potassium permanganate. As the 

 above reaction appears to yield the gas in a very pure state, M. 

 Moissan has made determinations of its density, and finds it to 

 be 3*03. The calculated density of PF3 is 3 "08. When a 

 measured quantity of the gas is heated over mercury in a closed 

 glass vessel, it is totally decomposed by the silica of the glass, 

 and the volume diminishes by one-fourth, four molecules of 

 PF3 becoming converted into three molecules of gaseous silicon 

 tetrafluoride, SiF4. 



The additions to the Zoological Society's Gardens during the 

 past week include a Ring-tailed Lemur {Lemur catta) from 

 Madagascar, presented by the executors of Dr. Allen ; a Vulpine 

 Phalanger {Pkalangista vulpina ? ) from Australia, presented 

 by Mr. W. H. Seward; a Hamster {Cricetus frumentariusy 

 from Russia, presented by Mr. Harold Hanauer, F.Z.S. ; an 

 Alligator {Alligator mississippiensis) from Florida, presented 

 by Mr. A. B. Archer ; a Hoffmann's ?>\o'Cc\.{Cholopus hoffmanni) 

 from Panama, deposited. 



OUR ASTRONOMICAL COLUMN. 



Objects for the Spectroscope. 



Sidereal Time at Greenwich at 10 p.m. on February 3 = 

 7h. 35m. 32s. 



Remarks. 



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

 follows : — " Pretty bright ; considerably small ; round ; very 

 gradually a very little brighter in the middle ; mottled as if 

 with stars ; almost planetary." The spectrum of the nebula 

 has not yet been recorded. 



(2) Duner describes the spectrum of this star as a very fine 

 example of the Group II. type. He states that all the bands 

 2-8 are wide and dark, especially 2 and 3, and that the whole 

 spectrum is well developed. No mention is made of the 

 presence or absence of absorption lines, but there is little doubt 

 that some will be found if looked for, the predominance of the 

 bands 2 and 3 probably indicating that the star belongs to a. 

 later species, and is therefore approaching Group III., in which 

 line absorption is predominant. Observations of the green and 

 blue carbon flutings are also suggested (see p. 305). 



(3) This star has hitherto been described as having a spectrum^ 

 of the solar type. The usual observations, as to whether the 

 temperature of the star is increasing (Group III.) or decreasing 

 (Group VI.) are required. 



(4) Gothard classes Procyon with stars of Group IV., but the 

 Henry Draper Memorial photograph of the spectrum seems to 

 indicate that it would be more properly described as an early 

 stage of Group V., differing from the solar spectrum in having 

 the hydrogen lines more developed and the metallic lines slightly 

 thinner. Further observations of the visible spectrum are 

 suggested. 



(5) According to Duner the spectrum of this star belongs to 

 Group VI., and shows the usual three absorption bands of 

 carbon. Band 6, which appears to be the most variable, is stated 

 in this case to be very dark, and the question is, Are there any 

 other variations in the spectrum accompanying the condition in. 

 which band 6 is dark ? It seems probable that the number 

 and intensities of the secondary bands will be found to vary 

 with band 6, and these should, therefore, receive special 

 attention. 



(6) This variable has a spectrum of the Group II. type, but 

 Duner does not give a complete description, as he probably did 



