270 



• KNOWLEDGE • 



[Jan. i'7, 1882. 



npimrpntly myBti>rioii« cnsc«, ono must haTo full and complete 

 ovidimco, not only of times nnd ncaBonp, but of all other c-ircuni- 

 KtiinroH conncft«Ml with each caw. 'I'hero must lie no shadow of 

 disoropancy~no lack of comiiloti- and full ajfrocniont in every jot 

 nnd tittle of ovidenco, boforo a sciontiBt can take the ease under liiv 

 coiiaidoration. 



To lay the explanation of Rnch cnBeff within the domain of 

 the }«upomatunil, lieeauso we may not ho able exactly to Katiafy 

 others or oursoIvoH of a rational cause for them, is, of course, 

 hut a sorry way of escaiK- from our diflioilties. But I have, at 

 least, ono idea to fall back upon in treating of so-«illo^l *' warniiiir 

 dreams," and tho appearance of apparitions at expected and uiiex- 

 pi"Cte<l times, and that is, the idea of coincidrncen. If a persim tells 

 me ho dreamt of a person's death, nnd that the person can bo 

 proved to have died at tho moment ho dreamed of the event, or 

 even if he tolls mo ho saw the ajiparition of his deceased friend, I 

 reply that ho may bo indulfrinj,' in the fallacy of post hoc evjo 

 propter hoc. I would further reply—being a disbeliever in 

 "ghosts" of all kinds as visitations from the nether world, at 

 least — that the explanation of these events does not lie outside the 

 doctrine of coincidences. It is, in other woixls, a mere fortuitous 

 circnmstance that tho dream or the " ghost " (i.e., tho subjective 

 image in one's own brain) has apjieared at the time (not always 

 exact) of the person's death. If I can show that as startling coinci- 

 dences occur in our waking life, I m.iy claim to have, at least, shown 

 tho possibility and probability of their occurring in the case of dreams 

 and ghosts. Here is ono well-known coincidence, as startling to my 

 mind as any ghost story 1 liave ever heard. I quote from my 

 recently published " Natnralist's Note-Book " (Chatto & Windus), 

 page 39 : — "The well-known case of Joseph Lesurqnos, whose mis- 

 fortune forms tho incident on which more than one melodrama and 

 novel has been founded, has recently been brought anew under 

 jiublic notice through Mr. Henry Irving's perfoi-maHce in the 

 ' Lyons Mail,' and by liis assumption of the dual rule of Lesurques 

 and his villainous double. The case actually occurred in France in 

 1791-, and its details are sufficiently well known to obviate the 

 necessity for their repetition here. Charged with robbery and 

 murder, tho innocent Lesurques was recognised, identified, and 

 sworn to as the real culprit by various disinterested wit- 

 nesses. Notwithstanding strong exertions which were made 

 to save his life, and, despite his previous high moral cha- 

 racter and probity of conduct, Lesurques was sentenced to 

 death, and executed. Soon afterwards, tho real culprit, a man 

 who bore the closest possible likeness to Le.«nrqnea, was brought to 

 justice. It wag then seen that the similarity in features, statuic, 

 build, and manner was so close as to havo deceived the witnesses 

 who gave evidence at the trial. On those grounds alone, and as a 

 matter of common recognition and identitication, the unfortunate 

 resemblance of Lesnniues to the real culprit had xmwittingly led 

 them into a ' Comedy of Errors,' which resulted in a legal tragedy 

 as its denouement. But more extraordinary to relate still is the in- 

 cident, well-nigh nnparalleled in tho annals of coincidences, that 

 Lesurques was inarked by a scai- on the forehead, and by another 

 on the hand, whilst the real criminal likowi.se possessed similar 

 markings. Surely " the grim irony of Fate "could no further go 

 than this, in cansing chance likeness to assume a form and to 

 entail consequences so fatal and sad as in the case of Joseph 

 Lesurques." 



And, lastly, as to a " ghost " being seen by more than one pei'son, 

 or regarding the possibility of several persons being collectively 

 deceived, lot mo relate the famous case of the Crystal Palace fire. 

 When the wing of the Palace was burnt the animals in the menagerie 

 were believed to have perished in the flames. But, as the flames 

 progressed, the enger and excited crowd of spectators were horrified 

 to behold the chimpanzee struggling to escape from a horrible 

 death on one of the piimacleaof the building. With eager eyes ihe 

 crowd followed every movement of tho ape, and loud was the 

 sympathy for the unfortunate animal. Imagine the seqnel. When 

 the chimpanzee was more nearly approached, the object which, to 

 the eyes of thousands, had presented tho exact reproduction of an 

 ape, was discovered to be merely a fluttering rag of canvas, the 

 movements of which had sinnilnted in their eyes the attitudes of the 

 monkey. .\fter tho occurrence of such an incident, I nmst be 

 pardoned if I feel somewhat scejitical, even when the united testi- 

 mony of two or three jiersons is hurled at my head by way of con- 

 vincing me that a ghost was thereby necessarily proved to be no 

 more ligment of the brain. " AxniiKW Wilson. 



Poin>*9 ExmAOT is a certain ear© for Khoumatitira and Gout. 

 Pond'd Eitrnct in a certain euro for Hiemorriioids. 

 PoiiH'8 Kxrriict JH n cerlain euro for »iirfil:.'ic ntiins, 

 Pond'8 Extract »ill h.-iil Ilunin and Wounils. 

 Pond'e Extract will cure Sprains nnd Bniiiier>. 



Sold by all CheraiBts. Get the f^onuine. 



ARTIFICIAL INDIGO. 



IT may be IntcroHting to many readers of this magazine to know 

 something about the production <if the dycHtulT indigo by 

 artificial means, for it is now to some extent obtained pmctically 

 by the cheniical process known as synthesis, from one of the con- 

 stituents of the tar obtained from tin- distillation of coal for the 

 production of gas. 



Previous to the introduction of this colouring mutter into Europe, 

 about the middle of the sixteenth century, the indigo contained in 

 wood (haliii linctorin) was employed lor dyeing, although the 

 Roman.s and Greeks used indigo for painting; up to tho present 

 time the name " wood" is still in vogue in many dyeworks, tho 

 vats in which tho dyeing is carried on being culled "wood vats" 

 and tho dye-house " wood-house." 



The following is intended to give a short account of the manner 

 in wkich this valuable colouring matter, so largely produced in 

 India from the cultivation of the indigo jilant, is bnilt np by 

 chemical processes. ludigo is comjiosed of carbon, oxygen, hy- 

 drogen, and nitrogen, and is represented by Uic formula C'gHjSO, 

 showing the number of atoms of each of its clementarj" consti- 

 tuents. The naphtha obtained wlien coal tar is distilled, contains a 

 nuTuber of chemical comjjonnds — benzol, toluol, cumol, A'c. ; it is 

 from the second of these (toluol, C;H„) that indigo is obtained. By 

 adding an atom of oxygen to indi^ro, Krdmann and Laurent formed 

 a compound named isatin (CgUjXO^,); and aftenvards Baeycr 

 succeeded in converting this comjiound back again into indigo 

 by the reduction of its cliloride ; and from a knowledge of 

 the constitution of this isatin, the two chemist.''. Claissen 

 and Skadvvell, have succeeded in building it up from a nitro 

 compound of benzoic acid (called ortho-niti-o-bcnzoic acid). It is 

 pretty well known that this acid is contained in gum benzoin, 

 from which it was exclusively obtained until within the last few 

 years. Now, however, it is produced froni toluol by simple but in- 

 teresting chemical processes. The nitro-compound of benzoic acid 

 has one of its hydrogen atoms displaced by chlorine, and on bring- 

 ing this chloride in contact with silver cyanide, the chlorine and 

 cyanide exchange places, forming the insoluble compound silver 

 chloride and the nitrite. This nitrite, heated with potassium 

 hydrate, exchanges the cyanogen for an atom of oxygen and hydrogen, 

 producing ortho-nitro-phenyl-glyoxalic acid and potassium cyanide. 

 The oxygen associated with the nitrogen forming the nitro group, 

 is displaced by a similar process to one already largely employed 

 for converting the nitro compounds of benzol, toluol, A'c, into their 

 corresponding amines or amido compounds (aniline toluidine) ; that 

 is, by contact with nascent hydrogen by the abstraction of water 

 from the amido compound just formed from ortho-nitro-phenyl- 

 glyoxalic acid isatin is obtained, which, as we have already seen, can 

 be converted into indigo by the process discovered by Baeyer. 



This chemist has also succeeded in producing isatin by another 

 process from toluol, first pi-oducing phenyl-acetic acid. 



The colouring matter is obtained pi-actically by Baeyer from a 

 compound found in gum, benzoin, and other natural products, 

 known as cinnamic-acid. This is the proces-s employed : — The acid 

 ])roduced by natural means being too expensive, its synthesis is 

 resorted to ; toluol is also, in this instance, the staiting-point j it is by 

 the substitution of one of its atoms of hydrogen by chlorine, converted 

 into a compound named benzyl chloride, which, by a iirojier treat- 

 ment with nitric acid, is converted into oil of bitter almonds by the 

 displacement of one atom each of the monatomic elements, hy> 

 drogen and chlorine, by the diatomic element o.xygen. This oil 

 is also called benzaldehyd. It was discovered in 1856 by Bertag- 

 nini that this compound, on treatment with acetyl-c'iloride, is 

 converted into cinnamic-acid. W. U. Pcrkin, F.R.S.. has, how- 

 ever, discovered a more practical and cheaper method for tho 

 synthesis of this acid. Two atoms of hydrogen in the toluol are 

 substituted by two of chlorine, forming benzyl-dichloride. and this 

 compound, heated with acetate of soda, yields cinnaroic acid. 

 Acting on this acid with nitric acid there is formed a nitro-com- 

 pound — the ortho-nitro-cinnamic acid. This is caused to combine 

 with two atoms of bromine, by which the dibrom-nitro-phenyl- 

 propionic acid is obtained. By the trr'utnient of this last-named 

 compound with caustic soda or potash, the two atoms of bromine 

 are removed, forming sodium bromide, whilst two atoms of hydro- 

 gen are also removed, forming a molecule of water, thus producing 

 a new compound having two atoms of bromine and two of hydrogen 

 less than the last-mentioned comjiound, the new jiroduct beinf; 

 oriho -nitro -phenyl - propiolic -acid, and this, by reduction with 

 hyilrogen, forms indigo, carbonic acid, and water. It is the 

 ortho - nitro • phenyl - ]u-opiolic - acid which is supplied to the 

 calico printers, who, on printing its .■ilkaliue solution with a 

 reducing agent, form an indigo white on the fabric, and on 

 steaming it is oxydised into the ]<\tw indigo blue. M. Rosen- 

 tiehl siiys, "n mixture of gnni water containing tho above- 



