January 2, 1893.] 



KNOWLEDGE 



A VOLATILE SERIES OF METALLIC 

 COMPOUNDS. 



By C. F. TowNSEND, F.C.S. 



THE progress of chemical science is continually 

 bringing to light new wonders and startling 

 paradoxes. Nothing more remarkable and 

 unexpected has occurred in the recent history of 

 chemistry than the discovery of the compounds of 

 nickel and iron with the gas generally known as carbon 

 monoxide or carbonic oxide. The new compounds are 

 called respectively nickel and iron carbonyls, and have 

 evidently a great future before them. Judging from 

 chemical precedent, one would quite as soon have expected 

 oil and vinegar to form a homogeneous mixture as a com- 

 bination of the bodies referred to. In fact, so anomalous 

 did it appear when Mr. Ludwig ]\Iond first brought the 

 accidentally discovered nickel compound to the notice of 

 the Chemical Society in the middle of 1890, that many 

 almost refused to believe in the possibility of its existence. 

 However, there is no doubt about it. Nickel carbonyl, a con- 

 siderable quantity of which was exhibited at a cimnTSinidm' 

 of the Royal Society held in -June last, and also at the 

 meeting of the British Association, is obtained by merely 

 passing carbon monoxide — a product of the incomplete 

 combustion of coke or charcoal, and which may often be 

 seen burning with a lambent blue tlame at the top of a 

 clear tire — over the finely divided metal, and condensing 

 the resulting vapour in a tube surrounded with ice and 

 salt. Its properties have been very fully investigated botli 

 by its discoverers, Messrs. Mond, Langer, and Quincke, 

 and also by M. Berthelot, who published his results in the 

 Comptrs riendu.s. 



It is a liquid of very high refractive power and brilliant 

 appearance, and considerably heavier than water, under 

 which it may be kept without change, provided the vessel 

 is completely filled and the water contains no air. It 

 solidifies at 13° F., and boils at 109^ F., and the vapour, if 

 lighted, burns with a strongly luminous tlame, which 

 appears smoky in consequence of the separation of metallic 

 nickel. The liquid is very volatile, and if the vapour is 

 suddenly heated a sharp detonation is caused. A mixture 

 of nickel carbonyl with air takes fire if brought into 

 contact with a very hot body, and occasionally explodes. 

 A mixture of the dry vapour and oxygen may be detonated 

 by simple agitation over mercury, and strong oil of vitriol 

 produces the same effect in a few minutes. The vapour, 

 when heated to 358'^ F., splits up again into its original 

 constituents, the metal and the gas, and the nickel deposits 

 itself as a brilliant coating on the sides of the vessel. 

 Advantage is taken of this circumstance to apply the 

 carbonyl to nickel-plating, and a patent has been taken out 

 by its discoverers for working it on a commercial scale. 

 At the last meeting of the British Association, Mr. Ludwig 

 Mond described the various uses to which the discovery 

 might be put, and the possibilities which it opened up. 

 The nickel-plating can be accomplished by simply exposing 

 the goods, after being heated to the temperature just 

 mentioned, to nickel carbonyl vapour, and solid articles 

 can be similarly formed by passing the vapour through 

 heated moulds. For this jjurpose, it is found advantageous 

 to dilute the vapour considerably with air. Nickel can also 

 be deposited on any substance by treating it with the liquid 

 itself, or better, by nickel carbonyl dissolved in suitable 

 solvents. These processes possess a great advantage over 

 electro-plating, as not only metal, but any substance, 

 however intricate in design or fragile in structure, 

 can be coated with a brilliant film of nickel by its means 



without the tedium and risk of first covering it with 

 a surface of blacklead. Some very beautiful specimens 

 of real flowers, plated with different metals, principally 

 gold and silver, so as to bring out the various parts of 

 their structure, were exposed for sale at the Frankfort 

 Electrical Exhibition. A syringa blossom, for instance, 

 would have its stamen and anthers plated with gold, its 

 corolla with silver, and the stalk and calyx with copper. 

 Needless to say, they found a ready market. The field 

 before this new process is practically unlimited, for not 

 only could it be applied to ornaments and articles of 

 household use, but, if required, to delicate muslins, and 

 dress or other fabrics. 



The liquid nickel carbonyl is highly poisonous, and, if 

 injected siibcutaneously, acts very powerfully on the animal 

 system, producing an immediate and remarkably prolonged 

 fall of temperature. It might, perhaps, be introduced 

 into medical practice as an antipyretic in the treatment of 

 fevers, were it not for the difficulty of administering it in 

 sufficiently small doses, and its intensely poisonous action. 

 The carbon monoxide alone is the active agent in causing 

 this effect, the symptoms being those of respiratory poison- 

 ing ; and the blood of animals killed by it exhibits the same 

 appearances as that of persons suffocated by inhaling the 

 fumes of burning charcoal. This kind of poisoning is par- 

 ticularly dangerous, and in cases of recovery the effects do 

 not wear off for several hours after. The red corpuscles 

 of the blood owe their colour to a complex chemical sub 

 stance known as hagmoglobin, which acts as the carrier of 

 oxygen. In passing through the lungs oxygen is taken 

 up, and it is converted into oxy-luemoglobin, which, when 

 placed so as to intercept the rays of light in the spectro- 

 scope, gives quite different absorption bauds to the h;emo- 

 globin itself; from the lungs the oxygen is carried to 

 different parts of the body to be exchanged for carbonic 

 acid, which is brought back to be eliminated and again 

 replaced by oxygen, thus completing the cycle. Carbonic 

 oxide combines with the htemoglobin to form carboxy- 

 haemoglobin, an exceedingly stable substance which can 

 only be displaced by oxygen with the greatest difficulty. 

 The consequence is that the blood is unable to perform its 

 functions, and the animal rapidly dies from suffocation. 

 The absorption spectrum of this last body is remarkably 

 characteristic and quite unmistakable, forming an infallible 

 test in case of suspected poisoning by charcoal fumes. 

 The vapour of nickel carbonyl is as deadly as the liquid, 

 and is dangerous in air even to the extent of only 0-.5 

 per cent. 



The extraction of the metal from its ores is another 

 valuable use to which the discovery of this compound will 

 almost certainly be put. The principal sources of nickel 

 are the copper-coloured arsenical mineral which the German 

 miners — after working it unsuccessfully for years in the 

 hope of obtaining copper — called kupfer-nukii (iu\, false 

 copper), and in which the metal was first discovered by 

 Cronstadt in 17-51, and s/n-isn, an impure residue formed 

 at the bottom of the melting-pots in the manufacture of 

 the bright blue pigment known as smult, which is largely 

 used by paper-stainers. Metallic nickel is obtained f'-om 

 these by heating them with charcoal in a furnace, but the 

 product only contains about BO per cent, of the pure metal. 

 It appears now that it will be sufficient to pass carbon 

 monoxide over the crushed mineral, and by simply heating 

 the resulting nickel carbonyl to 358^ F. chemically pure 

 nickel will be deposited. 



All attempts to obtain a similar compound with other 

 metals for a long time proved unsuccessful. As it seemed 

 improbable that nickel should be the only metal forming 

 such a compound, the investigators persevered with the 



