58 



NATURE 



[November 17, 1892 



in none of the photographs was the symmetrical diagonal 

 movement of the successive threes disturbed between 

 the 2nd and 12th pairs of legs inclusive. This apparently 

 simultaneous motion of three adjoining legs may probably 

 be explained by supposing a series of waves, whose crests 

 traverse three legs in the nijth of a second, to be passing 

 along the body, since the different photographs show 

 different legs moving in threes ; thus in one photograph 

 the 6th, 7th, and 8th on the left side are seen to be moving 

 forward, while in another the 5th, 6th, and 7th, are 

 moving. 



Since reading the paper at the Royal Dublin Society, 

 Mr. G. H. Carpenter brought to my notice two papers by 

 M. Jean Demoor, " Recherches sur la Marche des 

 Insectes et des Arachnides" {Archives de Biologie, 1890) 

 and " Recherches sur la Marche des Crustacds " {Archives 

 de Zoo logic Expcritnentale et Gencrale, 1891). M. 

 Demoor points out the simultaneous use of the tripod in 

 the insects which he examined, but as he did not use 

 photography he does not seem to have observed the minute 

 want of synchronism of the legs of a tripod. Figs. 4 and 5 

 illustrate this.* These are two photographs taken of the 

 same specimen of Blaps mucronata. Fig. 4 is from a photo- 



graph taken with a long exposure, and shows the ist and 

 3rd of the left side, and the 2nd of the right moving at the 

 same time, just as it appears to the eye. Fig. 5 is from 



a photograph taken with less than half the exposure of 

 4, and shows that while the ist leg on the right side is 

 raised off the ground, the 3rd on the same side and the 

 2nd on the left have not yet been raised. That they 

 have not been raised and are now come to rest is shown 

 by their backward position with regard to the body and 

 other legs. These two photographs also show that the 

 antenna is often twitched almost simultaneously with the 

 motion of the ist leg of its side. M. Demoor also ob- 

 served a scorpion {Buthus australis), but its method of 

 progression does not seem to have agreed with that of 

 the scorpions {Btithus europceus) which I observed. He 

 has not, so far as I know, recorded any observations on 

 spiders. Henry H. Dixon. 



Trinity College, Dublin, June. 



ON IRON ALLOYS. 



'T^HE merely mechanical expert in the working of 

 ■■■ metals would naturally consider it probable that a 

 given metal when fused with another would communicate 

 Its physical properties, roughly, in proportion to the 

 quantity added. A soft, tough metal added to iron would, 

 from his point of view, render the latter softer ; a brittle 

 or hard metal would have the contrary effect, and so on 

 throughout the whole series of metallic alloys. 



I Figs. 4 and 5 show the legs, which are raised from the ground, quite 

 sharp. In the negative they are more or less blurred owing to their motion 

 during the exposure. 



Actual experiment would soon, however, show the 

 fallacy of this, and that in the majority of cases no reli- 

 ance could be placed on this assumption solely based on 

 the physical properties of the elements severally con- 

 sidered. A further study of the laws which govern 

 chemical combination would quickly show that alloys 

 formed by fusion were not merely intermixtures, but that 

 something else took place, bodies being often produced, or 

 rather formed, differing considerably from the metals 

 severally used. It would therefore be fair to assume that 

 the metals entered into combination with each other, and 

 yet it would be found that the problem even at this stage 

 was not completely solved. 



Further inquiry and experiment would indicate that it 

 was not always possible to prove that chemical combina- 

 tions " were in all instances " formed by fusion alone. 

 Instead of this something closely akin to only an inter- 

 mixture of the metals occurred ; second, one of the metals 

 had apparently dissolved in the other ; third, it was diffi- 

 cult to differentiate betwixt intermixture and solution. 

 Here we are on all fours with modern ideas which seem 

 to have met with general acceptance, although it is not 

 denied that elements or metals are capable of chemically 

 combining with each other. We are not, however, quite 

 prepared to draw a hard and fast line betwixt chemical 

 combination of the metals with each other, solutions, 

 and intermixtures of metals. One appears to merge into 

 the other, and no good reason " so far as is known" 

 can be given why solution, as ordinarily understood, or 

 as defined by Van 't Hoff and others, may not be as 

 applicable to fused metals as to the solution of certain 

 salts in water. 



Water at 60° is nothing more nor less than fused ice ; 

 fused iron, therefore, may obey the same laws, and, " like 

 water," may be capable of dissolving certain substances, 

 and rejecting others, temperature constituting the sole 

 difference — or plainly, solid ice is fusible at 60°, iron 

 at about 2500". 



Now what happens in the case of water? Certain bodies 

 are soluble in it, others not ; on lowering the temperature, 

 these bodies are to a certain extent rejected, and nearly, 

 but not quite, pure ice is formed ; and so far as we know 

 this equally applies to fused iron. As an instance, on 

 cooling, the carbon is rejected, and appears in the 

 graphitic ^ form, merely diffused throughout the solid 

 cold metal. It is impossible here to treat this matter in 

 detail ; but enough, we think, has been said to indicate 

 that the analogy is fairly complete throughout. 



But there is another matter— apart from the solution 

 of foreign bodies in fused ice or iron — which requires to 

 be discussed. Ice dissolves in warm water, and so does 

 cold iron or steel in superheated fused iron ; the hot fluid 

 metal from the Bessemer converter fuses or dissolves 

 large lumps of solid steel placed in it as easily as ice is 

 thawed in warm water. Temperature here, in both in- 

 stances, determines the quantity which can be added ; 

 the higher the heat, the greater the quantity which can 

 thus be dissolved or fused, ere the bath becomes thick, 

 pasty, and incapable of being poured out into another 

 vessel. 



In so-called solutions the same rule appears to hold 

 good ; but, as all chemists know, there are many excep- 

 tions ; in some cases heat is evolved, in others absorbed ; 

 and some bodies are more soluble in the cold fluid 

 solvent. 



It is, however, believed that no instance can be quoted 

 of a body being more soluble in iron at a low degree of 

 heat than at a high one. Confining ourselves to hot fluid 

 iron or steel, it apparently readily dissolves cold metal. 

 Similarly, other bodies, such as copper, &c., are dissolved 

 in the same way when added to it. 



The cold metal is fused by absorption of the enormous 



' The relations existing betwixt carbon and iron are peculiar, and 

 require to be separately discussed. 



NO. 1203, VOL. 47j 



