NA TURE 



\_yune 2, 1 88 1 



addition of hydrocbloiic or sulphuric acid diminislies the liievo- 

 rotatoiy action, and eventually converts it into a marked dextro- 

 rotatory one ; addition of acetic acid has a similar, but much less 

 marked effect ; v\ith asparagine a point is reached at which the 

 solution, in acetic acid, is optically inactive. 



Attention «as recently drawn in these "Notes" to an 

 attempt made by Th. Thorasen to show that the numbers 

 expressing the specific rotatory powers, of various carbon com- 

 pounds might be expressed as whole multiples of certain funda- 

 mental constants ; each of these constants was supposed to be 

 characteristic of a group of allied compounds. Thomsen's 

 methods of calculation have been severely criticised by Landolt 

 (in the Bciichtc), who has shown that from the limited accurate 

 data at our disposal such an attempt as that of Thomsen can 

 only be regarded as a play on numbers, and is devoid of all 

 scientific value. 



Experiments are described in the May number of the 

 Jmtrnal of the Chemical Society by Jones and Taylor, which 

 appear to leave little doubt that these chemists have succeeded 

 in preparing a gaseous hydride of boron, and that the probable 

 formula of this compound is BH3. The new compound— the 

 existence of which establishes another point of analogy between 

 boron and the nitrogen elements— is prepared by decomposing 

 magnesium boride by a dilute acid ; the gas has only been 

 obtained largely mixed with hydrogen ; it burns with a green 

 flame, and is decomposed by heat with deposition of boron. 



In the course of a paper on the appearance of nitrous acid during 

 the evaporation of water (Chem. Soc. Journal), by Warrington, 

 experiments on the detection of this acid, by the use of hydro- 

 chloric acid and naphthylamine hydrochloride, are described, 

 which show th;it one part of nitrous acid is easily detected in 

 10,000,000 parts of water, and that as small a quantity as one 

 part in 1,000,000,000 can be detected. 



In the Zeitschrift fiir anal. Chem. Herr Seelheim describes 

 experiments on the percolation of waters through soils, from 

 which he draws the following general conclusions :— Only that 

 stratum of any soil which is composed of the smallest particles 

 need be considered in determining the permeability by water 

 of the soil of a district. The composition of a soil must be 

 ascertained, otherwise experiments on a large scale furnish no 

 measure of the peruiaabil.ty of that soil. The thickest stratum 

 of sand allows the passage of many hundred times more water 

 than a layer of clay only one centimetre thick. The permea- 

 bility of dykes may be regulated by inserting layers of clay 

 between layers of sand. 



Small quantities of carbon monoxide may be detected, e.g. 

 in the air of rooms, by drawing the suspected gas over powdered 

 glass moistened with diluted blood, shaking the blood with a 

 drop of ammonium sulphide and examining by the spectroscope. 

 Strips of |japer soaked in a solution of o"2 gram, palladium 

 chloride in 100 c.c. water serve to detect carbon monoxide : the 

 dried slips are suspended by platinum v\iies in a large flask with 

 a very little water, and the flask is corkei ; with five parts of 

 carbon monoxide in the atmosphere of the flask, a black shining 

 deposit of metallic palladium appears on the paper in a few 

 minutes ; with one part, in two to four hours ; and with o"5 

 part, in from twelve to twenty-four hours. 



A USEFUL historical account of the investigations made on 

 the subject of dephosphorising pig-iron, appears in Dingier' s 

 polytechnisches Journal, and in abstract in the May number of 

 the Journal of the Chemical Society. 



The rate of chemical reactions having been lately the subject 

 of several investigations and discussions, M. Kayander publishes 

 in the Russian Journal of the Chemical and Physical Society 

 (vol. xiii. fascicule 4), the results of his last measurements. 

 Without seeking to establish theories as to a connection between 

 chemical affinity and the rate of reactions, M. Kayander simply 

 tries to make mea urements in a branch of chemistry insuffi- 

 ciently worked until now. To simplify the results he has em- 

 ployed a solid body and a liquid one, and has measured the rate 

 of dissolution of magnesium in various acids ; the magnesium 

 was taken in the shape of small plates, having a surface of about 

 2000 square millimetres ; the acids, in solutions of O'Oi of 

 the atomic weight (in gi-ammes) in a litre of water. Experi- 

 ments as to the infiueiice of various degrees of concentration 

 will be published in a second paper. As to the influence of 

 time, he arrives at the conclusion that the reaction begins at 

 tlie very moment of the immersion of the magnesium in the 



acid ; acids when mixed produce the same action as if taken 

 separately. As to temperature, its influence is precisely that 

 which it exercises on the diminution of the internal friction 

 of the particles of the liquid against one another, and does not 

 seem to uifluence the chemical properties of the reacting bodies ; 

 the figures M. Kayander has arrived at fro.n a long series of 

 measurements establish that the speed of the reaction is inversely 

 proportional to the internal friction of the medium. The re- 

 searches will be continued. 



PHYSICAL NOTES 



On heating a plate of boracite lately Herr Kleiu (Gdtt. Soc. 

 of Sci.) was surprised to observe a complete change of the 

 optical image. The boundary lines of the optical fields 

 prove variable with temperature, and often wholly disappear, 

 perhaps reappearing in quite different places. Herr Klein con- 

 cludes from these and previous observations that boracite does 

 not owe its origin to a tMin-like formation of parts of lower 

 symmetry, but is regular, and produces simple individuals ; and 

 the optical properties, apparently in sharp contradiction to this, 

 are really due to tensions produced in growth. These divide the 

 crystal into parts of different tension, of which the sometimes 

 stronger suppress the weaker, for certain temperatures and 

 po itions of the crystal. (Similar properties in crystals of 

 analcime have been described by Herr Ben Saude to the Gottingen 

 Society.) 



An ingenious, somewhat complex, apparatus, named an auto- 

 matic methanometer, or automatic analyser of fire damp, has 

 been recently brought before the Geneva Physical Society by 

 Prof. Monnier (Arc/i. des Sci., April 15). The fire-damp, in 

 presence of air in excess, is decomposed in a glass vessel by a 

 platinum wire rendered incandescent, and the condensation pro- 

 duced acts directly on a mercury manometer, having platinum 

 wires inserted in its tube. The air of the mine is automatically 

 forced by bellows, every hour and half hour, into the burner. 

 The receiving apparatus stands in the central office. The system 

 includes several electro-magnets, tv\o batteries, pendulums with 

 escapement, an alarm-bell, &c. 



The influence of pressure on the electric conductivity of metal 

 wires has been studied anew by M. Chwolson (Imp. Acad, of St. 

 Petersburg Bull., March) ; Wartmann's jirevious experiments, in 

 which wires w ere compressed between steel plates with caoutchouc 

 lining, having failed to show whether pressure changes the specific 

 resistance. M. Chwolson used a piezometer, giving pressures 

 up to 60 atmospheres, the wire being wound round a glass tube, 

 then passed through it, and the tube inserted in another, which 

 was connected with the piezometer. (The two wire ends were 

 brought out through binding screws.) Among other results, at 

 3'S C. the copper wire showed a relative diminution of resistance 

 of about o '0000013 by one atmosphere of pressure; a hard 

 brass wire about o'oooooil; and a lead wire (at 7° C.) about 

 o'ooooii, or ten times more than the brass. Pressing at 17° C. 

 the calorific action preponderates over the direct action of 

 pressure for copper and brass, while the reverse occurs with 

 lead. Moreover, the author proves, in the case of the brass wire, 

 that the pressure causes change of the specific resistance besides 

 change of the resistance through change of the length and 

 thickness. Every relative change of volume involves a relative 

 change of the specific resistance about 3'6 times as great. 



M. Mascart showed recently how the phenomenon of Tal- 

 bot's fringes could be applied to measurin ; the refractive indices 

 of gases and the difierence between the refractive index of a 

 solid and that of a liquid. M. Hurion has further thus mea- 

 sured the difference of the refractive indices of liquids, and in 

 the Journal de Physique for April he shows how the refractive 

 index of a liquid may with those fringes be directly determined. 

 The two interferent rays are rendered vertical, so as each to 

 traverse one of the halves of a ]3artitioned rectangular vessel 

 with glass bottom. The liquid being first at the same level in 

 both divisions, its level in one is gradually lowered by a special 

 contrivance, and this has the effect of displacing the fringes in 

 the field of the tele cope. Let e be the variation of level, / the 

 number of fringes that have pas ed a point in the field corre- 

 sponding to light of wave-length A, thenf(OT-i) =/A. The 

 letter m represents the refractive index of ihe liquid for light of 

 wave-length A. (For further details we refer to M. Hurion's 

 note.) 



