64 



NA TURE 



[May 19, 1892 



gas being colourless, and endowed with an odour somewhat 

 reminding one of that of carbonyl chloride. In contact with 

 water, acetyl fluoride is found to react eventually in a manner 

 similar to its well-known analogue, acetyl chloride, forming 

 hydrofluoric and acetic acids. 



CH3.COF + H„0 = CH3.COOH + HF, 

 But there is a considerable difference in the degree of energy 

 with which the decomposition occurs, for while the behaviour 

 of acetyl chloride is almost violent, acetyl fluoride only reacts 

 with great slowness. When a small quantity of the fluoride if 

 dropped into water the two liquids do not mix, and the globule of 

 fluoride only disappears after long standing. Strong solutions of 

 potash or soda, however, decompose it rapidly, with formation of 

 fluoride and acetate of the alkali. The action of caustic lime 

 upon acetyl fluoride is interesting ; the gas is rapidly absorbed 

 by it, and calcium fluoride and acetic anhydride formed. 



2CH3.COF + CaO = CaFj, + (CH3.CO)20. 

 Ammonia gas reacts with considerable energy with the liquid, 

 producing a white crystalline mass, consisting of ammonium 

 fluoride and acetamide, CH3.CONH2. The latter may readily 

 be isolated in good crystals by extraction with ether and sub- 

 sequent evaporation. The gaseous fluoride reacts with ammonia 

 in the proportion indicated by equation — 



CH3.COF + 2NH2 = CH3.CONH2 + NH4F ; 

 that is, two volumes of ammonia react with one volume of 

 acetyl fluoride gas. Aniline likewise acts with energy upon 

 the liquid, forming hydrofluoric acid and acetanilide, 

 CgHg.NH.CHj.CO. The action of absolute alcohol is pecu- 

 liar ; it dissolves the liquid fluoride in all proportions, but after 

 an interval of a few hours, interaction occurs with production of 

 hydrofluoric acid and acetic ether. The latter may readily be 

 separated by the addition of water. 



CH3.COF + C2H5OH = CH3.COOC2H5 + HF. 

 Acetyl fluoride is much more stable in presence of alkaline 

 acetates than its chlorine analogue. Even after four hours' 

 heating in a sealed tube to 100° with sodium acetate, only a 

 small proportion of sodium fluoride and acetic anhydride were 

 formed. Still more stable is acetyl fluoride towards sodium 

 amalgam, there being no appreciable reduction to aldehyde or 

 alcohol. Metallic sodium is likewise without action upon 

 liquid acetyl fluoride, but when heated to redness in the gaseous 

 fluoride, the metal decomposes it with incandescence, sodium 

 fluoride being formed and carbon deposited, together with a few 

 drops of a liquid whose characters have not yet been ascer- 

 tained. From these reactions it is evident that acetyl fluoride 

 is a substance of a much more stable character than its analogue, 

 acetyl chloride. 



The additions to the Zoological Society's Gardens during 

 the past week include an Egyptian Ichneumon {Herpes tes 

 ichnetimon) from North Africa, presented by Dr. J. Anderson ; 

 a Ring-tailed Coati (Nasuarufa), a Kinkajou {Cercokptes caudi- 

 volvuhis), a Blue-bearded Jay [Cyanocorax cyanopogon) from 

 Brazil, presented by Mr. J. E, Wolfe, C.M.Z.S. ; two Laughing 

 Kingfishers {Dacclo gigantea), from Australia, presented by Mrs. 

 H. M. Stanley ; two Grey Hypocoliuses {Hypocolius ampe- 

 linns i ? ) from Scinde, presented by Mr. W. D. Gumming ; 

 two Ravens {Coii'us corax), British, presented by Mr. Gregory 

 Haines; a Crowned Horned Lizard {Phrynosoma coi'onatum) from 

 California, presented by Mr. R. Thorn Annan ;a Common Fox 

 (Cants vulpes), British, three Palm Squirrels {Sciurus palmaruni) 

 from India, a Brown-throated Conure {Conurus ccruginosus) 

 from South America, deposited ; a Grey-headed Porphyrio 

 {Porphyrio poliocephalus) from Persia, purchased ; a Persian 

 Gazelle {Gazella subgiUterosa t5 ), a Vulpine Phalanger {Phalan- 

 gista vidpina ? ), born in the Gardens. 

 NO. I 177. VOL. 46] 



OUR ASTRONOMICAL COLUMN. 



Latitude Observations at Waikiki. — The Hawaiian- 

 Gazette for March 8 contains an account by Mr. Preston, of the 

 U.S. Coast Survey, of the latitude observations which are being 

 made at Waikiki on the island of Oahu, Hawaii. In it we 

 read : — " The motion of the pole is, of course, extremely small, 

 and the effect is that here in Honolulu we are about 50 feet 

 nearer the equator now than we were some months ago. This 

 change does not, however, go on indefinitely, but the motion 

 is such that the pole returns at the end of a year to nearly its 

 original position. Besides this annual movement, there seems to 

 be reason to believe that there is a secular change extending over 

 a period ofat least sixty years." But no definite conclusions can be 

 arrived at until the observations made at Honolulu are discussed 

 in connection with those made on this side of the earth. In 

 order to test the theory that changes of latitude are produced by 

 the movements of large masses of molten matter in the interior 

 of the earth, the force of gravity is measured on every night 

 that latitude observations are made. As this is done with the 

 idea of detecting variations, the relative and not absolute in- 

 tensity is all that is required. The arrangement employed is 

 such that if from any cause the acceleration due to gravity 

 should be increased by only one five-hundredth of an inch, it 

 could be easily measured. The observations will be completed 

 in the fall of the year, but the final results cannot be known 

 before the latter part of 1893. 



Motion in the Line of Sight. — Astronomy and Astro- 

 Physics, No. 104, contains a very important contribution by 

 Mr. W. W. Campbell, on the reduction of spectroscopic ob- 

 servations in the line of sight. The paper contains an explana- 

 tion of the construction and use of the tables, the limit of 

 precision adopted being one-hundredth of a mile per second. 

 The first table gives the velocities of the star corresponding to a 

 known displacement of one tenth-metre in the various parts of 

 the spectrum, from which the velocity corresponding to any 

 observed displacement can be directly obtained. The formula 



Vs = V^A\ 

 gives this velocity corresponding to any measured AA., V^ being 

 taken directly from the tables. 



Table II. gives the earth's orbital velocity, V„, and the devia- 

 tion, i, when the sun's longitude is ©. These values are 

 obtained from the formulae — 



tan.-- ^«in(0-n) 



and 



V„ = 



I -f <f cos( O - n) 

 ?5[r + ^cos(© - 



tt)] sec i. 



and when found are substituted in the equation — 

 v„— - V,j sin (A - O -f i) cos iS. 



By tabulating V^ and i as functions of O, their values can be 

 very easily found, and Va consequently reduced from the last- 

 mentioned equation. 



The value of the lunar correction has been taken into account 

 here, omitting any errors due to ellipticity of the orbit and its 

 inclination to the ecliptic. Its value is obtained from the for- 

 mula — 



Vd— — 0*29 sin t cos 5 cos 9, 

 the latitude used being that of Mount Hamilton, but corre- 

 sponding corrections for any other latitudes can be found from 



these by multiplying them by ^''--?_, where ^' is the new lati- 



COS (p 



tude required. 



The Late Partial Eclipse of the Moon. — Fine weather 

 was generally prevalent during the partial eclipse of the moon 

 on May 11, affording many observers a good opportunity for 

 noting any new features connected with such an occurrence. 

 Considering that the eclipse was only a partial one, it may be 

 rather difficult to decide whether it should be classed in the 

 category of "bright" or "dark" eclipses. Undoubtedly it 

 was not a very dark one, for during the greatest immersion the 

 whole surface of the moon could be distinctly seen, especially 

 with the help of a telescope, with which craters could be picked 

 out. On the hypothesis that "dark" and "bright" eclipses 

 are brought about owing to the different states of the solar 

 atmosphere, the present one should have been at any rate more 

 inclined to be " bright " than " dark," for as we are approach- 



