December 28, 1893] 



NA TURF, 



209 



kept at full speed ahead, the collision would have been 

 averted. 



A FURTHER communication concerning the explosive metallic 

 derivatives of acetylene is contributed to iht American Chemical 

 Journal by Dr. Keiser. He has previously shown that the 

 compounds obtained by the action of acetylene upon ammon iacal 

 solutions of cuprous chloride and silver nitrate possess the com- 

 position CnCu, and C^Ago, and that they are to be regarded as 

 substitution products of the hydrocarbon. The action of acety- 

 lene upon aqueous and alkaline solutions of mercuric salts has 

 since been studied, and the results are now published. When 

 acetylene acts upon silver nitrate, either in aqueous or ammo- 

 niacal solution, the same product, CoAgo, appears to be pro- 

 duced. But in the case of mercuric salts the action appears to 

 be essentially different in aqueous and alkaline solutions. 

 When acetylene is led through a solution of mercuric chloride 

 in water, a white granular precipitate is produced, which is not 

 explosive after drying, and which does not dissolve in dilute 

 acids with evolution of acetylene gas. This compound contains 

 chlorine, and is represented by the formula Co(HgCl).2. If, 

 however, acetylene is passed into an alkaline solution of a 

 mercuric salt, such as Nessler's solution, mercuric iodide dis- 

 solved in potassium iodide with the addition of caustic potash, 

 a white flocculent precipitate is obtained, which when dry is 

 extremely explosive and dissolves in dilute hydrochloric acid 

 with evolution of acetylene. It is analogous in all its proper- 

 ties to the silver and copper compounds, and is a metallic sub- 

 stitution product of the same type, CgHg. This compound can 

 only be obtained in the pure state by the use of pure acetylene, 

 such as that prepared by treating ethylene dibromide with 

 alcoholic potash. Decomposition of the substance commences 

 at about ioo°, and when it is rapidly heated to a temperature 

 slightly higher than this it explodes with extreme violence, 

 leaving a small residue of iinely divided carbon and mercury. 

 It is particularly interesting to learn that when the substance 

 is treated with an alcoholic solution of iodine it unites with the 

 latter, slowly even at the ordinary temperature and rapidly at 

 the temperature of a water-bath, forming di-iodo-acetylene. 

 Cola- This compound upon standing a short time polymerises, 

 and the polymer separates in the form of crystals which melt at 

 187' and appear to be hex-iodo-benzene, Cgltj. 



In the course of an investigation concerning the atomic 

 weight of copper, Messrs. Richards and Rogers, of Harvard 

 University, have observed that cupric oxide prepared by ignition 

 of the nitrate always contains a considerable amount of occluded 

 gas, chiefly nitrogen, while that prepared from the carbonate 

 invariably shows no sign of occluded gas. This fact is of con- 

 siderable importance inasmuch as the previous determinations 

 of the atomic weight of copper are affected by it and will be 

 rendered more or less inaccurate. It is no new observation, 

 however, for it was pointed out by Frankland and Armstrong 

 as long ago as 1868, but appears to have been largely overlooked. 

 The Harvard chemists show, moreover, that the phenomenon 

 is also exhibited by oxides of zinc, nickel, and magnesium, 

 when prepared by ignition of the nitrate. In the case of mag- 

 nesia the amount of occluded gas is extraordinarily large, ex- 

 ceeding a hundred cubic centimetres from ten grams of oxide. 

 Hence it is considered necessary that the atomic weights of 

 these metals should be subjected to revision, taking account of 

 these facts, and until this is done the values hitherto accepted 

 can only be considered as approximate. 



The additions to the Zoological Society's Gardens during 



the past week include a Mona Monkey {Cercopithecus mona, 9 ) 



from West Africa, presented by Mrs. Frances Bell ; a Bonnet 



Monkey {Macacus sinicus) from India, presented by Mr. Henry 



NO. I 26 I, VOL. 49] 



Vane ; three Black-backed Jackals {Canis mesomelas) from 

 South Africa, presented by Mr. J. Matcham ; four Bemicle 

 Geese (Bernicla leticopsis), 2i, 2?) European, a Variegated 

 Sheldrake {Tadorna variegata) from New Zealand, presented 

 by Sir Henry Peek, Bt. ; a Little Auk {Mergullus alle) 

 British, presented by Mr. J. W. C. Stares ; two Adorned 

 Ceratophrys {Ceratoplirys ornata) from Buenos Ayres, pre- 

 sented by Miss IMildred FitzHugh ; a Mozambique Monkey, 

 {Cercopithecus pygerythriis) from East Africa, deposited ; six 

 Smooth-clawed Frogs [Xetiopiis lavis) hatched in the Gardens. 



OUR ASTRONOMICAL COLUMN. 



Small Distances Measured with the Heliometer. — 

 As the filar micrometer measures very precisely distances of 

 a few seconds, so with equal accuracy does that important 

 of modern instruments, the heliometer, measure distances 

 ranging from a few minutes up to one or two degrees. 

 With the former instrument one brings the thread (moved by the 

 micrometer head) first to one side of the slar and then to the 

 other ; or, if one has two threads, one places the star half-way 

 between them, and thus reads off the distance. With the 

 heliometer the distances are read off the scale at the object- 

 glass end (from the eye end), the images of the two stars cast by 

 the movable half of the object-glass being placed symmetrically 

 first on one, and then on the other side of the images from the 

 fixed half. 



In the measurement of small distances with the heliometer it 

 has been found that nearly every observer measures the distances 

 too small, thus a small positive correction has to be applied to 

 the observations. As an instance of the magnitude of the 

 corrections to be added or subtracted for various distances, we 

 give the following table : — 



The necessity of such a correction has long been known, 

 but its cause is yet unexplained, although suggestions, such 

 as that of Dr. Gill, have been put forward. In Astroiiomische 

 Nachrichten, No. 3197, Prof. Wilhelm Schur gives an interest- 

 ing account of his investigations, which had for their aim the 

 determination of the source of this error. Observations showed 

 him that the explanation suggested some time back by Dr. Gill 

 was not valid, at any rate for the Gottingen heliometer : it was 

 finally thought that an explanation might be found by supposing 

 an irregular guidance to occur to those parts of the instrument 

 which carry the objective, but on investigation it was found 

 that such was most improbable. Irregularity in the objective 

 slides themselves was also eliminated, as the magnitude of the 

 error necessary to produce such a large difference in the distance 

 measured was too large to be at all considered. In the paper 

 Prof. Schur is led to discuss some of the measurements made in 

 the triangulation of the Praecipe, and he refers to the method he 

 adopted to bring all the measures into harmony. Three ways 

 were open to him to satisfactorily accommodate the distances in 

 this work, they being, in the measurements of the three arcs, the 

 employment of quantities which are too small to be of no 

 account in the measures of distances in the large quadrilateral. 

 Development of the formula on the assumption (as the observa- 

 tions indicate) that at the distance 1300" a maximum in the 

 correction occurs, and for o' and 5000" the "verbesserung " is o, 

 and a is assumed to be o"'473. -^nd lastly, the computation of 

 the "verbesserung" after the expression o"'264 5., which assumes 

 a change in the scale value, which change, although inadmissible 

 for large distances, bringi^, in the case of the distances here 

 concerned, the measurements into a more satisfactory concord. 



