Dec. 21, 1876] 



NA TURE 



167 



It will be remembered that Prof. Newcomb communicated his 

 principal result to the Royal Astronomical Society last summer 

 (see "Monthly Notices," vol. xxxvi. p. 358). 



Prof, Forster's Scientific Lectures. — Under the title 

 Satnmluno wissenschaftlicher Vortrdge, there has lately appeared 

 a series of seven lectures on astronomical subjects by the director 

 of the Royal Observatory at Berlin. It includes an address on 

 "The Astronomy of Antiquity and the Middle Ages in Relation 

 to Modern Development," notices of Copernicus and Kepler 

 and the'r works, &c. 



CHEMICAL NOTES 

 Variations In the Critical Point of Carbon Dioxide 

 IN Minerals, and Deductions from these and other 

 Facts, — Mr.W. N. Hartley has continued his experiments on this 

 subject, and gives in a paper read lately before the Chemical 

 Society further conclusions as to the existence of the expansible 

 fluids in mineral cavities. He concludes it to be carbon diox- 

 ide from the spectrum produced by the electric spark in a tube 

 containing such gas as was liberated by the decomposition of the 

 minerals ; the turbidity produced by crushing quartz under baryta 

 water (Vogelsang and Geissler, 1869); the rate of expansion of 

 the liquid in sapphire compared with that of carbon dioxide 

 (Sorby and Butler, 1869) and the determinations of the critical 

 point made by himself in 1875-76. To determine the critical 

 point he uses small thermometers ma?e specially for the purpose, 

 one having a range from — 20 to 140° F,, the other graduated 

 to register tenths of a degree from 25" to 33° C. The following 

 table shows all the variations noticed in the critical point of car- 

 bon dioxide existing in various minerals : — 



Topaz ... 

 Topaz . . 

 Topaz . . . 

 Tourmaline 

 Tourmaline 

 Sapphire 

 Sapphire 

 Sapphire 

 Rock crystal 

 Rock crystal 

 Rock crystal 

 Rock crystal 

 Rock crystal 

 Rock crystal 

 Beryl ... 



Critical point. 



28° c. 



28° C. and 26°'S 



27°-S5 



27»-27 



26°- 9 



between 30° '5 and 31* 



between 25 '5° and 26' 



29°-5 



30°" 95 



30' -95 



32°-5 



33°7 



39° 



30° -95 



30° -92 



He discusses, from his conclusions, certain ideas with regard 

 to the formation of diamonds, and believes that it is difficult to 

 suppose that they are entirely formed by a process in which 

 unoxidised forms of carbcn are intermediate products, otherwise 

 they would occur not unfrequently in the neighbourhood of coal 

 formations. The theory that diamonds are produced by reducing 

 agents on carbon dioxide very highly compressed and acted on at 

 temperatures much above its critical point, introduces a condition 

 of things highly suggestive of further speculation, and of experi- 

 ments subject to conditions under which no chemical reactions 

 have ever been made in the laboratory, 



Thermo-Chemical Researches.— Julius Thomsen has 

 found in some recent investigations that gold presents allotropic 

 modifications according to the nature of the solutions from which 

 it is obtained, and the reagent with which it is precipitated. The 

 modifications he has examined are gold precipitated from 

 solution of the chloride and bromide respectively by sulphurous 

 aci-f, and that precipitate! from the sub-chloride, sub-bromide, 

 and sub-iodide. These modifications differ in the amount of heat 

 evolved by each in similar reactions. As the energy shown by 

 the gold precipitated from solution of the chloride by sulphurous 

 acid is less than in the other cases, this amount is taken as the 



standard. The energy of the gold precipitated from the bromide 

 is greater by 3 •200 iheat units, and that precipitated from the 

 sub-chloride, sub-iodide, or sub-bromide by 4 700 heat units per 

 atom. 



Tiieine in Te.\. — As the amount of theine varies in various 

 kinds of tea (according to different analyses) from one to six per 

 cent., the question naturally arises whether the quality of tea 

 does not depend upon the amount of theine it contains. Some 

 time ago M. Claus arrived at the conclu.sion that the inferior 

 kinds of tea contain altogether more theine than the higher, 

 pointing out especially that the cheapest, the so-called brick-tea 

 used in Mongolia and Siberia, and prepared from all kinds of 

 refuse as dead leaves, stalks, &c., contains far more theine (3*3 

 to 3 '6 per cent.) than the higher qualities (10 to i'3 per cent.). 

 M , Markovnikoff, of Moscow, now arrives at different ■ results. 

 Having made a series of analyses^of one kind of tea by the various 

 analytical methods used until now, for ascertaining their compa- 

 rative values, he proves the deficiency of most of these methods. 

 Ether, for instance, extracts but one-third of the whole amount of 

 theine, and benzole, one-fourth. Using, then, a more perfect 

 method, and analysing six kinds of tea, selected from the highest 

 and from the lowest qualities, he arrives at the result that the 

 amount of theine in them varies but very little, from 2"o8 to 

 2 "44, and that it regularly increases, with one exception, with the 

 quality of tea, whilst the amount of ash giveri by each kind regu- 

 larly decreases from 6'i to 57 per cent. The differences being, 

 however, very small, M. Markovnikoff supposes that the quality 

 of tea does not depend, or depends very little, upon the amount 

 of theine, and far more upon the quantity of tannic acid and 

 aromatic oils it contains, but that on the whole the teas made 

 from younger leaves contain more theine than those made from 

 older leaves. 



Influence of Pressure on Combustion, — Some inter- 

 esting observations have been recently made by M. Wartha, 

 on the influence of pressure on combustion. He observed 

 the burning of six stearine candles in free air, and in an 

 iron case under a pressure of i '95 atmospheres. They burned 

 under this pressure with a flame 9 to 12 cm. long, and gave 

 much smoke ; their luminous power diminished, while the flame 

 assumed a yellowish-red colour. The decrease of weight after 

 one hour of burning was found to be less than in burning in 

 free air. This last result is opposed to the observations of 

 Frankland, who has affirmed that the consumption of the burning 

 material of a candle, or the like, is not perceptibly dependent on 

 the pressure of the medium in which the combustion occurs. It 

 is supposed that the difference of pressure in Frankland's experi- 

 ments (on Mont Blanc and at Chamounix) was not sufficiently 

 great to give a distinct difference in consumption of the burning 

 matter. M. Wartha further put a candle to burn under an air- 

 pump receiver, with special apertures, and, with increasing 

 rarefaction, the flame was seen to enlarge, and its luminous 

 power to diminish. At a pressure of 90 mm,, the greatest 

 rarefaction produced, the luminous power was quite gone, and 

 the flame, which had now assumed threefold size, appeared to 

 consist of three parts, an inner bluish-green cone with a violet 

 sheath, and a weakly violet mantle. The diminution of the 

 luminous power in this case M. Wartha explains by the fact that 

 under less pressure less of the products of combustion are sepa- 

 rated in the form of soot. 



BIOLOGICAL NOTES 

 The American Bisons. — An important quarto memoir on 

 the living and extinct Bisons of America, from the pen of Mr. J, 

 A. Allen, has just been issued from the University Press of 

 Cambridge, Massachusetts, It is illustrated by twelve plates ?.nd 

 a map of North America, in which the distribution of the bison 



