February 14, 1895J 



NA TURE 



2>7: 



being given to forestry, and because the Society is making 

 efforts to increase its membership by going further afield. The 

 Transaciions o( the Society, of which we have received a re- 

 cent issue (vol. iii part iv.), should materially assist towards 

 this end ; for the instructive papers contained therein appeal to 

 all foresters. In the Part received by us, there is an c^say on 

 " How Trees Grow," by Mr. J- Maughan ; an essay on 

 "Thinning Mixed Plantations," by Mr. \V. Forbes; and a 

 paper on " The Distribution of Trees in a Wood," by Prof. W. 

 Somerville. These are all useful contributions, but even more 

 important is the publication of the results of an inquiry, con- 

 ducted by the Society, into the disease of the Larch, a subject 

 about which much has been written and said. The information 

 •which Prof. Somerville has brought together, forms a valuable 

 summary if the present position of knowledge in regard to 

 the Larch disease, and shows the various conditions and 

 cultural methods which hold out some prospect of securing 

 comparative immunity from attack. With a larger membership, 

 the Society would be able to carry out, and publish, the results 

 of many similar investigations. 



Pkof. Schiff and Dr. Tarugi describe, in a communication 

 to the Berichte, an admirable substitute for the disagreeable 

 sulphuretted hydrogen in qualitative analysis. The new re- 

 agent is the ammonium salt of thio-acetic acid, CH3 . COSNH^. 

 .\mmonium thio-acetale is decomposed by hot dilute hydro- 

 chloric acid, liberating sulphuretted hydrogen without any pre- 

 cipitation of sulphur. No objectionable bye-products are 

 formed in the reaction, only sal-amminiac and acetic acid being 

 produced. When a feebly ammoniacal solution of ammonium 

 thio-acetate is added to a hydrochloric acid solution of the 

 metals of the second group, and the liquid is heated to near 

 boiling, the metals are at once precipitated as sulphides, while 

 only the faintest odour of sulphuretted hydrogen is perceptible. 

 After cooling and filtering, the filtrate is found lo contain no 

 trace of the metals, not even of arsenic if an arseniate had 

 been originally present. The completeness and rapidity of the 

 reaction, particularly in the case of arsenic, which is usually sd 

 troublesome to precipitate fr om arseniates, is one of its strongest 

 recommendations, and is described by Prof. SchifT as being 

 perfectly surprising. A couple of cubic centimetres of a 30 

 per cent, solution of ammonium thio-acetate is usually ample 

 for a gram of the substance to be analysed. The reagent has 

 been employed for sometime by Prof Schiff in the Pisa labora- 

 tory, and is much appreciated by his students, sulphuretted 

 hydrogen being completely excluded fro'U the laboratory, 

 doubtless to the material advantage of all concerned, both as 

 regards comfort and health. Thio-acetic acid is readily pre- 

 pared by acting upon glacial acetic acid with phosphorus 

 pentasulphide. It boils at 95', and is but slightly soluble in 

 water. When the acid is dissolved in a slight excess of dilute 

 ammonia, a yellow solution is obtained, which is then diluted 

 to three times the volume of the acid originally taken -that is, 

 10 cubic centimetres of the acid furnish 30 cubic centimetres 

 of the reagent. Prof. Schiff serves the reagent out to his 

 students in small bottles close I by a cork, through which a 

 small pipette, holding 2 cubic centimetres, is inserted, by means 

 of which the convenient quantity of the reagent can at once be 

 added to the hydrochloric solution of their test substance. It 

 is scarcely necessary to add that zinc, manganese, nickel, and 

 cobalt are not precipitated in the presence of hydrochloric acid 

 by the new reagent, any more than by sulphuretted hydrogen 

 itself. The sulphides of these metals are al once precipitate 1, 

 however, upon rendering the solution alkaline ; but as 

 ammonium sulphide acts quite as well for this purpose. Prof. 

 Schiff confines the use o( ammonium thio-acetate to the pre- 

 cipitation of the metals of the second group. 



NO. 1320, vor, 51] 



The additions to the Zoological Society's Gardens during the 

 past week include a Lion {[■'di^ Lo, i ) from India, presented 

 by H.R. H. the Duke of C^onnaught ; a Cape Bucephalus (Buce- 

 phalus capensis) from South Africa, presented by Mr. J. E. 

 Matcham. 



OUR ASTRONOMICAL COLUMN. 



The Mass OF THE Asteroids. — A preliminary note on the 

 probable mass of the asteroids was contributed by Mr. B. M. 

 Roszel to the yohns Hopkins Universily Circular in May 1894, 

 and summarised in these columns (N.\TURE, vol. 1. p. 87.) In 

 that paper Mr. Roszel limited himself to determining the mass 

 from a study of 216 minor planets ; he has now extended the 

 computations to 311 asteroids, the orbits of which are given 

 in the Berliner Astronoiiiiiches Jahrbuch for 1894 {University 

 Circular, January 1895). His chief object was to find a probable 

 limiting value for the mass,rather than an accurate determina- 

 tion of the mass itself. Using the photometric determinations 

 of the diameter of Vesta, by Pickering and Miiller, and the 

 direct measures of the diameters of Ceres, Pallas, and Vesta by 

 Barnard, Mr.Roszel has reduced the volumes of all theasteroids 

 to the volume of Vesta, except when Barnard's measures were 

 the basis, in which case he computed the volumes of Ceres and 

 Pallas separately, and added them to the combined volume of 

 the remaining 309. Assuming the albedo constant and a con- 

 stant density equal to the density of Mars, he obtained the 

 following numbers : 



Combined volume of 311 asteroids . 5185 vol. of Vesta. 

 ,, ,, omitting Ceres and 



Pallas. . . 2684 ,, ,, 



Volume of Vesta, in terms of volume of Mars : 



(1) From Pickering's estimate of the diameter 



of Vesta, assuming the albedo = albedo 



of Mars . . ' --- 000022 



(2) From Mailer's estimate, assuming {«) the 



albedo = albedo of Mars . . . = 000065 



(3) From Mliller's estimate, assuming (b) the 



albedo = albedo of Mercury . . . = 000129 



(4) From Barnard's estimate of the diameter of 



Vesta = 000018 



Combined mass of 3 1 1 asteroids, in terms of mass 

 of Mars : 



From Pickering's estimate, as above . = 0001 12 



,, Mliller's estimate, as above (a) . . = 0-00336 



,, ,, ,, ,, (/') . . = O'oo666 



,, Barnard's measures . . . . — 000273 



The mean diameter of Mar^ was taken as 4230 miles. It 

 appears from the above numbers that the combined mass of 

 the asteriods is about '026 of the muss of the moon. 



The Apparent Diameters ok Mercury. — During the 

 transits of Mercury on May 9, 1891, and November 10, 1894, 

 Prof. Barnard gave special attention to measurements of the 

 planet's apparent diameter. {Ast y cwr. No. 335.) In both cases 

 the diameter in R. A. was found to be slightly greater than that 

 in declination, and if this be not a mere accidental coincidence, 

 as Prof. Barnard seems rather inclined to believe, it would 

 indicate a small polar compression. The measures at the two 

 transits respectively indicate a polar compression of 1/134 and 

 1/98, or a mean of 1/116. Though by no means insisting on 

 the reality of the difference in the diameters. Prof. Barnard 

 points out that " the results may be of great importance in the 

 future, as hearing upon the rotation of the planet on its axis in 

 a reasonably short period." Expressed in angular measure, 

 reduced to unit di>tance, the two diameters as measured in 

 1894 were 6''24I for the "equatorial," and 6 '178 for the 

 " p )lar " diameter. It is incidentally mentioned that " though 

 Mercury cannot be seen at transits with lire naked eye alone, it 

 only requires apowerof 2\ diameters to make it easily visible. " 



The Variation of Latitude.— The results obtained by 

 Mr. Chandler in his investigations of variation of Latitude seem 

 to be confirmed by M. Ivanof's recent discussion of the older 

 series of observations made with the great vertical circle at 

 Pulkowa. (.Ji/. y^M?-. No. 335). " There is no doubt that two 

 periods subsist ; one equal to 428 days, the other to a year. 

 Also, the semi-amplitudes of both terms are variable beyond 

 any doubt." 



