134 



HARDWICKE'S SCIENCE-GOSSIP. 



GOSSIP ON CURRENT TOPICS. 



By W. Mattieu Williams, F.R.A.S., F.C.S. 



ARTIFICIAL SILK.— I have often pondered on 

 the humiliating fact that, in spite of all our 

 modern chemistry, we are still dependent on a 

 caterpillar for the production of the most beautiful of 

 our fabrics, the one that would be also the most useful 

 if it were cheaper. We know that it exists within the 

 silkworm as a liquid which, by some process of 

 oxidation or evaporation, or probably of both, be- 

 comes a tenacious solid immediately it is exposed to 

 the air. We know its ultimate chemical composition, 

 and also that it is derivable from nearly every kind 

 of leaf that grows, as nearly all are eaten by some 

 species of caterpillar, and caterpillars generally are 

 silk-producers. 



We also know that it is obtainable from animal 

 matter, as the flesh-feeding spider also produces it. 

 Not only these, but a multitude of the inhabitants of 

 fresh and sea-water also produce silk. The threads 

 of the various species of mussel, the tubular cases of 

 many species of marine worms, and some of the 

 caterpillar-like caddis worms, are made partially or 

 wholly of a material of silken character. This is 

 also liquid before ejected, and its solidification under 

 water is still more remarkable than that of the 

 sub-aerial silk spinners. 



We are now told that M. de Chardonnet has 

 produced an imitation of silk by adding to an 

 etherized solution of the material of gun-cotton 

 (nitrated cellulose) a solution of perchloride of 

 iron, and to this mixture a small proportion of 

 a solution of tannic acid in alcohol. This is 

 filtered and then forced by gentle pressure through 

 a fine tubular orifice, dipping into water acidulated 

 with nitric acid. The issuing fluid thus forms a 

 semi-solid thread which can be drawn forth and 

 then wound, after complete solidification by passing 

 through a dry air space. It is grey or black, but 

 may be dyed. The thread thus obtained is described 

 as tenacious, supple, transparent, and of silky appear- 

 ance and touch, and is not attacked by acids or 

 alkaloids of moderate strength, but is soluble in 

 etherized alcohol and acetic ether. The account I 

 have read does not tell us whether it has been used as 

 a varnish, which from the above description appears to 

 be its most promising application. 



Cotton and other fibres covered with an adherent 

 film of such material would serve as the basis of 

 beautiful fabrics, and it might even be made into 

 waterproof sheets by simply painting it over surfaces 

 to which it would not adhere, and then skimming off 

 the film. 



When we remember the small beginnings of some 

 of the greatest achievements of applied science, this 

 effort of M. de Chardonnet is very promising. Others 

 will doubtless proceed with the problem, and how- 



ever great may be their success by improving upon 

 this first step, let us hope that the pioneer will not 

 be forgotten in awarding the honour and profits that 

 may follow. 



The Colouring Matter of Blue John.— 

 Every visitor to the Matlock district of Derbyshire 

 and its catch-penny shows of abandoned lead work- 

 ings that are exhibited as natural caverns, and its 

 twopenny tolls for walking on highways and 

 byways, is familiar with "Blue John," specimens 

 of which are largely sold there, and some of it 

 is actually found in the neighbourhood. It is a 

 variety of fiuor spar (Calcium fluoride) in which the 

 blue tint is very deep and beautiful. The composi- 

 tion of the colouring matter has remained unex- 

 plained until lately. On the ioth of April last, Mr. 

 A. Norman Tate read a paper before the Liverpool 

 Geological Society, in which he showed strong 

 reasons for concluding that the colour has an organic 

 origin. If the further investigations that are pro- 

 mised confirm this, other questions will be opened, 

 such as whether the organic matter is of animal or 

 vegetable origin, and of what class, and how it came 

 thus diffused through the mineral. It is by no means 

 necessary that the material which gives the blue 

 colour to the fluor spar shall itself be blue. This is 

 shown by the fact, that the most intense and brilliant 

 of all blue minerals, of all blue pigments, lapis 

 lazuli, and artificial ultramarine, are composed of 

 materials, none of which are blue, viz., silica, 

 alumina, soda, sulphur, lime, sulphuric acid, iron, 

 chlorine, and water or potash. 



A Prism of Flame. — Everybody knows that 

 prisms have been made of glass, and other refracting 

 solids, and all who have given any special attention 

 to the subject also know that fluids such as carbon 

 bisulphide have been formed into prisms by enclosing 

 them in glass walls, and that spectra have thus been 

 obtained corresponding to the dispersive powers of 

 the material of the prism. A. Winkelmann has 

 recently gone further, has made prisms of flame 

 affording opportunities for examining the dispersive 

 powers of incandescent vapours thrown into the flame. 

 He tried to obtain prismatic flames by enclosing 

 them in plates of talc or mica, but failed, and finally 

 succeeded by using a Bunsen burner of triangular 

 section and placing on the top of the tube a double 

 thickness of wire gauze, and on that again a triangular 

 support smaller than the section of the burner. This 

 carries an iron cup in which is placed the sodium or 

 other material, the vapours of which are to be ex- 

 amined. By these means he obtained a special 

 anomalous dispersion when the flame was largely 

 charged with sodium and potassium vapours ; but 

 only negative results with other substances. This 

 failure he attributed to the insufficient density of 

 their vapours. 



