44 



NATURE 



[May ii, 1882 



florets were to be found in almost every instance, frequently in 

 great numbers, but usually overlooked from their great resem- 

 blance to scales of the root-stock. M. Battandier further stated 

 that the fruit was twice the size of those contained in the normal 

 capitula ; also that the root-florets were not cleistogamic, a fact 

 confirmed by finding specimens showing the anther-tubes and 

 stigmata projecting. Similar instances were also recorded as 

 occurring in two species of Scuipus and a Myosotis. 



CHEMICAL NOTES 

 The formula? deduced by Guldberg and Waage in their genera' 

 • theory of action of mass have been recently applied, with satis- 

 factory results, by R. Warder (Anier. Chan. Journ. iii. No. 5) 

 to the case of saponification of ethylic acetate. W. Ostwald con- 

 tinues his work in the same field ; he has recently studied the 

 actions which occur when certain pairs of salts are fused together 

 in equivalent quantities. His general result is that those salts 

 which have the greatest heats of formation are always produced in 

 greatest quantity, Berthelot's so-called "law of maximum work," 

 viz. that of several possible products of a reaction that salt, in 

 the formation of which most heat is evolved, is alone produced, 

 is regarded by Ostwald as erroneous ; if it were true, chemical 

 equilibrium would be established only in those exceptional 

 reactions wherein some of the reacting bodies underwent dis- 

 sociation. Berthelot's statement is a return to the old hard and 

 fast ideas on which "tables of affinity" were constructed, ideas 

 long ago overthrown by C. L. Berthollet (Journ. Prart. Chan. 



XXV. I). 



Data continue to be accumulated showing more definitely that 

 there exists a close connection between the structure of molecules 

 and the physical properties of the substances composed of these 

 molecules. Pawlewski has recently published a short account 

 of his researches on the " critical temperatures " of liquid com- 

 pounds : he states that the critical temperatures of isomeric ethers 

 are identical or very nearly so, that isomers containing " doubly 

 linked" carbon atoms have a higher critical temperature than 

 those in the molecule of which the carbon atoms are singly 

 linked, &c. (Bcrichte, xv. 460). 



In an important paper bearing on the same general subject, E. 

 Wilson states, as a result of his collation of many determina- 

 tions of specific gravities of solids, that it is not justifiable to 

 assign, as is usually done, a certain definite volume to each 

 elementary atom in a compound molecule, but that the volume 

 to be assigned to each atom in a compound molecule depends 

 on the nature of all the atoms in the molecule (Proc. A'. S., 

 32. 457)- 



In continuance of his experiments on the effects of pressure 

 on chemical changes — before referred to in these notes Spring 

 states that he has prepared Wood's alloy (melting at 65°) by 

 compressing, at 7500 atmospheres, iron filings, with bismuth, 

 cadmium, and tin, in proper propoitions. He has also obtained 

 Rose's alloy (lead, bismuth, and tin), and also brass, by pressure 

 of the constituent metals (Berichte, 15, 595). 



As the results of an extended series of observations on the 

 structure of metals, Kalischer (Baichle, 15, 702) concludes that 

 most of the metals are naturally crystalline, and that when the 

 crystalline structure has been lost by mechanical treatment it 

 can, in most cases, be restored by the action of he.it. 



PHYSICAL NOTES 

 7£An important contribution to physico-mechanical science has 

 been made by M. Benhelot in a memoir communicated to the 

 Academie des Sciences of Paris, upon the ra; idity of propagation 

 of a wave of explosion. An explosion in a gasecus compound 

 propagates itself, it would appear far more rapidly than a sound 

 wave could travel in the medium. For example, the velocity of 

 sound in mixed oxygen and hydrogen gases is 514 metres per 

 second, while the explosion propagates itself at 2S14 metres per 

 second. M. Berthelot concludes that the wave is therefore not an 

 acoustic wave at all, but a wave of chemical action. The character- 

 istics of this new mode of propagation appear to be the following : 

 uniform velocity of propagation (through tubes) ; independence 

 of this velocity of the material of the tubes ; tubes of lead and 

 gutta-percha of equal calibre conveying the explosion at equal 

 rates. The velocity in a capillaiy tul e is slightly less than in a 

 wide cue, being 2390 metres per second for oxyhydric gas as 



against 2S40 metres. The velocity differs in different mixtures, 

 being 10S0 metres per second in a mixture of oxygen and car- 

 bonic oxide. The velocity is independent of pressure which, in 

 the experiments varied from I to 3 atmospheres. M. Berthelot 

 attempts to identify this velocity with that of the translation of 

 the gaseous molecules at the temperature attained in the ex- 

 plosion, as calculated from the formula of Clausius — 



v - 29354 \l — (metres per second) ; 



where T is the absolute temperature and p the density at 0° of 

 the gas relatively to the air. He assumes T as 3000 in each 

 case, which would give for the oxyhydric mixture a velocity of 

 2000 to 2500 metres per second and 13CO for carbonic acid. M. 

 Berthelot therefore propounds the following view as to the way 

 in which explosive action is propagated. In the film of gas first 

 kindled a certain number of molecules are urged forward with a 

 velocity corresponding to the maximum temperature of the che- 

 mical combination. Their shock against the neighbouring films 

 determines there the commencement of chemical action, and so 

 the movement proceeds, a uniform rate being observed except 

 for those molecules which are close to the walls of the tube 

 which give up in the form of heat a portion of their kinetic 

 energy to the solid matter of the tube. A comparison with 

 certain properties of sound waves leads one to doubt the finality 

 of Berthelot's conclusion that these waves are not sound waves ; 

 for Regnault formed a similar retardation of sound-waves in 

 narrow tubes, and it is known that their velocity is independent 

 of pressure, and that it increases with an increase of tempera- 

 ture, and that the temperature which determines the velocity is 

 not the temperature of the mass as a whole but the temperature 

 of the molecules in the actual wave for the time being. The 

 recent experiments of Gallow ay and of Abel on the propagation 

 of an explosion in air charged with dust and contaminated with 

 gas appear to deal with quite another phenomenon, namely, the 

 velocity of spread of combustion in a space containing particle" 

 of solid matter floating in the air, and which has no more direct 

 relation to the velocity of sound than has the velocity with 

 which combustion is propagated along a train of gunpowder or 

 a piece of slow-match. 



Another contribution to experimental acoustics we owe to 

 Mr. John Le Conte of California, who has published in the 

 American Journal of Science some observations on sound- 

 shadows in water. More than fifty years ago, when Colladon 

 and Sturm were measuring the velocity of sound in the waters of 

 the Lake of Geneva, Colladon remarked on the extreme sharp- 

 ness with which an acoustic shadow was cast by a projecting 

 wall that ran out into the lake. The greater sharpness of 

 shadows might be expected from the mathematical theory of 

 undulations, for waves of higher pitch than for those of lower, 

 as the wave-lengths of the former are shorter, and therefore less 

 liable to diffraction at the edges of acou>tically opaque objects 

 Mr. Le Conte's experiments 'were almost all made with the 

 waves produced by the explosion of cartridges of nitroglycerine, 

 each containing 15 lbs. of the explosive stuff. These cartridges 

 were being used in blasting a shallow reef in the harbour of San 

 Francisco, and the means taken to observe the propagation of 

 the shock consisted in sinking soda-water bottles and glass tubes 

 hlled with air, so as to be wholly or partially concealed behiml 

 soliel objects such as wooden piles. A cartridge was exploded 

 about 40 feet away from a pile about 12 inches in thickness ; 

 behind this obstacle, and for a distance of 12 feet behind it, a 

 sharply defined sound shadow could be traced. Another instance 

 is given in the singular preservation of buildings on th? occur- 

 rence of an explosion at San Francisco when situated within the 

 geometrical shadow of other buildings. Mr. Le Conte seeks to 

 explain the relative sharpness of shadows of explosive sounds by 

 supposing that in this case the very short impulse gives rise to a 

 disturbance whose wave-length is exceedingly short. In connec- 

 tion with the subject, it may be worth while to recall Lord Ray- 

 leigh's beautiful experiment on the sound-shadow behind an 

 opaque circular disk, where (as in the case of light for which, as 

 predicted by Poisson and verified by Arago, there is a luminous 

 point at the centre of the shadow), at the centre of the acoustic 

 shadow, a perceptible augmentation of the shrill note of a bird- 

 whistle was observed. 



The old device of exploring the vibrating column of air in an 

 organ-pipe to ascertain the'position of nodes and loops, by letting 

 down into it a membrane of tissue paper on a wire frame, is 



