4 



KNOWLEDGE 



r.jANUARY 2, 1893. 



work, and finally succeeded in volatilizing distinct quan- 

 tities of iron in a current of carbon monoxide. The issuing 

 gas burneri with a yellowish flame, and if passed through 

 a heated tube deposited a metallic mirror in the glass, 

 which answered to all the tests for iron with unusual 

 brilHancy. The quantity produced was, however, very 

 small, and the process exceedingly laborious, for it took 

 no less than six weeks to volatilize about thirty grains of 

 iron. Even under the most favourable conditions the gas 

 never contained more than 02 per cent, of the compound, 

 but by varymg the details of the process a much larger 

 yield was obtained. 



The iron carbonyl thus produced is a pale yellow viscous 

 Hquid, nearly half as heavy again as water. It distils 

 without decomposition at 220" F., and solidifies below 6'^ F. 

 into yellowish needle-shaped crystals. It decomposes 

 slowly on exposure to air and, like the nickel compound, is 

 completely broken up by heating its vapour to 356" F. On 

 the other hand, it is much less active than its analogue 

 and is not attacked by dilute oil of ^-itriol. Its composition 

 was at first thought to be similar to that of nickel carbonyl, 

 but on accurate analysis it was found to contain five 

 proportions of carbon monoxide [Fe (CO).] instead of the 

 four which consticute the latter [Ni (CO),]. 



Whilst engaged in some experiments on the utilization 

 of water-gas (which is manufactured by passing steam over 

 red-hot coke, and contains about 40 per cent, of carbonic 

 oxide) for illuminating purposes by means of the Farnehjelm 

 system, in which a comb of magnesia is raised to incan- 

 descence by a number of fine gas jets. Sir H. E. Roscoe 

 and Mr. Scudder noticed that a red deposit of oxide of iron 

 was formed on the rods after the water-gas had impinged 

 on them for a few hours. This was a very serious drawback, 

 as the illuminating power became considerably reduced. 

 As the experiments were being conducted in a steel works 

 the first supposition naturally was that the stain was caused 

 by fine particles of iron present in the atmosphere, but closer 

 inspection showed that the deposit was of a " coralloid " 

 structure and must, therefore, have been produced by the 

 gas itself. In order to ascertain whether the iron existed 

 in the gaseous state or was carried forward chemically, 

 the gas was filtered through several tight plugs of cotton 

 wool. No difference, whatever, was observed and it was 

 concluded that the gas contained a very minute quantity 

 of a volatUe compound of iron. Shortly after it was sub- 

 jected to various chemical tests, which left very little 

 doubt as to its identity with iron carbonyl. 



Coal gas has also been found to contain iron, derived, 

 no doubt, from the slow action of the 7 or H '"/. of carbon 

 monoxide it contains on the iron of the mains and gas 

 pipes. This accounts for the hitherto unexplained black 

 stain so frequently observed on steatite and other burners. 

 Compressed coal gas has begun to take the place of 

 hydrogen in the production of lime-light, and the stain 

 formed on the lime cylinders is very noticeable, being, it 

 is almost needless to say, somewhat of a drawback to its 

 use. 



The discovery of this series of compounds is quite a 

 i-evelation to the metallurgical chemist, and already 

 explains many mysteries. In the cementation process for 

 the manufacture of steel, bars of iron are embedded in 

 powdered charcoal, and kept at about the melting point of 

 copper (2192'-' K.i for eight or ten days. Steel, as is well 

 known, is an alloy of iron, with a combination of carbon 

 and iron, called carbide of iron, and the principle of all 

 ateel-making is the same : carbon must be added to soft 

 iron in definite proportions. If the iron contains no carbon 

 it is comparatively soft and malleable. Wrought iron 

 contains less than 0-3 '',v, of carbon ; steel from 0-3 to 



1-5 7 : above this the metal takes the character of cast- 

 iron. The charcoal which surrounds the bars of iron in 

 the process just referred to, occludes a large quantity of 

 air in its pores, which, when heated, forms carbonic oxide. 

 This gas permeates the iron and gives up its carbon to the 

 metal, returning again to take up a fresh supply from the 

 charcoal, and thus acts as a carrier of carbon to and fro in 

 the interstices of the iron, which it gradually converts into 

 almost homogeneous steel, known technically as hlister- 

 fiteel, owing to its peculiar vesicular appearance caused by 

 the penetration of the gas. These compounds must play 

 a very important part too in the blast furnace, and in both 

 the Siemens and the Bessemer process, especially the 

 latter. Bessemer steel is made from cast-iron ; the carbon 

 and impurities are burnt out of it by driving a current of 

 air through the molten metal. When this has been accom- 

 plished, a highly carburetted cast-iron, called npiciiclcisen, 

 is thrown into the converter in properly regulated quantity, 

 and the carburation of the iron is rapidly eft'ected. 



Renewed attention has recently been directed to some 

 volatile compounds of platinum with chlorine and carbon 

 monoxide, which are broken up by water with deposition 

 of pure platinum, thus forming a possible way of extracting 

 the metal from its ores. If any discovery of this kind 

 were to facilitate the extraction of gold, which at its 

 present rate can barely keep up with the demands of the 

 increasing consumption, an immense boon would be con- 

 ferred on the civilized world. 



CATERPILLARS.-III. 



By E. A. Butler. 

 {Continued from pane 229, Vol.w.) 



IN some caterpillars the usual complement of ten 

 prolegs is greatly reduced, only the last two pairs 

 being present ; thus all the six central segments of 

 the body are left without means of support. This, of 

 course, necessitates a special method of progression, 

 the wave-like motion already described being clearly 

 impossible. Caterpillars of this kind take a firm hold 

 alternately with the two ends of the body, the central part 

 being by turns arched up and extended, as the animal 

 advances, not with the creeping motion of small paces, but 

 with the stately gait of long strides. Thus, when the 

 insect is in a fully extended position and wishes to advance, 

 it clings tightly with its six true legs, and then, releasing 

 its claspers and lifting the hinder part of the body, hooks 

 them on again close up to the legs, thereby causing the 

 intervening portion of the body to assume the form of a 

 perpendicular loop ; then, holding tightly by the claspers, 

 it lifts the legs and advances the fi'ont part to the fullest 

 extent, straightening out the loop and bringing itself again 

 into its former horizontal position. From tlieir peculiar 

 mode of walking, by curves and loops, caterpillars of this 

 kind are called geometers or loopers. They are always 

 long, narrow, thin-bodied creatures, usually green or brown 

 in colour, and often with the head divided on the crown 

 into two prominences like faint indications of horns. They 

 are noted for the extraordinary positions they assume, and 

 the remarkable way in which they mimic little twigs or 

 stems. When at rest, the body is usually kept straight 

 and stiff at an acute angle to the twig, inclined to about 

 the same extent as the twigs themselves are to the main 

 stem, the mechanical difdoulties of such a position being 

 met to some extent by an exceedingly fine thread of silk 

 stretching from the spinneret to the twig, or less frequently 

 by the anterior legs clasping another twig in the 

 neighbourhood. The silken thread provides means of 



