November 29, 1900] 



NATURE 



1 1 [ 



field, Illinois, 21 per cent. At Fort Smith, Arkansas, the 

 difference was 12 per cent., but with reversed conditions, 

 the upper air humidity being the higher. 



The vapour pressures were compared with others ob- 

 tained at various times at equal altitudes by means of 

 balloons and mountain observations, and found to be 

 somewhat lower. The average value was 59 per cent., as 

 compared with 68 for the balloon and 66 for the moun- 

 tain observations. In these data the vapour pressures 

 were represented in percentages obtained by the formula 



■^, p representing the vapour pressure at any given 



P\ 



altitude, and p" that observed simultaneously at the 



earth's surface. 



Differences in wind direction above and at the surface 

 were for the most part confined to a deflection toward the 

 right at the kite. This deflection frequently increased 

 with the altitude, but rarely exceeded 90 degrees. In 

 some few instances, chiefly during unsettled weather, Ihe 

 deflection was toward the left, but not to any great 

 extent. 



At the present time efforts are being made to obtain a 

 more improved and satisfactory vehicle for the meteoro- 

 graph. If such an one can be devised, it is yet possible 

 that the desire of the forecaster will finally be gratified 

 with great resultant benefit both to the cause of science 

 and to the world at large. H. C. Frankenfield. 



THE PRESENT CONDITION OF THE INDIGO 

 INDUSTRY. 



SINCE a previous article upon the above subject 

 (November i) was written,a report of the opening of the 

 Hofmann House in Berlin has appeared in the Times. At 

 the opening ceremony Prof, von Baeyer and Dr. Brunck 

 delivered lectures upon the synthetical production of in- 

 digo. Von Baeyer's lecture dealt chiefly with the theo- 

 retical side of the question, while that of Dr. Brunck, 

 who is one of the managing directors of the Badische 

 -Anilin und Soda Fabrik, dealt more upon the manufactur- 

 ng side. As the work of von Baeyer is so well known 

 and was referred to in the previous article, attention will 

 only be drawn to the extremely interesting speech of Dr. 

 Brunck. 



In the first place. Dr. Brunck drew attention to the 

 advantages of synthetic over natural or vegetable indigo, 

 owing to its uniformity of composition, fine state of 

 division, ready reducibility, &c. He claimed that a 

 much less skilled operator may be employed in manipu- 

 lating the dye bath than when natural indigo is used. 

 He then went on to describe the prejudice which the 

 synthetical indigo (" indigo pure ") had to contend with 

 when it was first placed on the market in 1897 ; it being 

 stated by some that it was merely specially refined 

 natural indigo, and by. others that it was a substitute 

 for indigo. It is extraordinary how difficult it is to make 

 the public believe that it is possible to prepare in the 

 laboratory a product which is identical in every respect 

 to one which is of vegetable origin. In the case of in- 

 digo, however, there is perhaps some excuse, because the 

 manufacturers of coal-tar products have often brought 

 out colours which dye practically the same shades as 

 indigo, but though not readily distinguished from it 

 even by experts, have lacked one of the chief character- 

 istics of indigo — fastness. But notwithstanding prejudice 

 and keen competition, the development of the manu- 

 factory has been enormous. Dr. Brunck states that 

 about 900,000/. has been invested in the indigo depart- 

 ment of the Badische Company, and that the quantity 

 of indigo now annually manufactured by this company 

 alone would require the cultivation of nearly 250,000 

 acres of land in India. 



The method of manufacture employed by the Badische 



NO. 1622, VOL. 63; 



Company is that of Heumann, in which phenylglycine- 

 ortho-carboxylic acid (anilido-acetic acid) is fused with 

 caustic soda {c.f. Nature, this volume, p. 9). When this 

 process was first discovered, the cost of the out-going 

 products was so great that indigo so prepared could not 

 compete with the natural product. The Badische Com- 

 pany employ more than 100 highly- trained research 

 chemists; to some of these the work of endeavouring to 

 elucidate the problem, how to manufacture phenylgly- 

 cine-orlho-carboxylic acid cheaply, was entrusted. Taking 

 naphthalene, which is obtained in enormous quantities 

 from coal tar, as starting product, the following process 

 was worked out. The naphthalene is oxidised by highly 

 concentrated sulphuric acid in presence of mercury or 

 mercury salts, with production of phthalic acid. The 

 phthalic acid is then, by a series of reactions, converted 

 into anthranilic acid which, when combined with mono- 

 chloracetic acid, produces phenylglycine-ortho-carboxylic 

 acid. During the oxidation of naphthalene with sulphuric 

 acid large quantities of sulphur dioxide are produced, the 

 loss of which would be a very serious expense. In pre- 

 paring indigo upon the scale in which it is now manu- 

 factured, from 25,000 to 30,000 tons of sulphur dioxide 

 are produced annually. But this is not lost ; it is mixed 

 with air and passed over heated oxide of iron, and is 

 thus by catalytic action converted into sulphuric anhy- 

 dride, and this by the action of water into sulphuric acid. 

 Chlorine is required in order to prepare chloracetic acid, 

 and caustic soda to fuse the phenylglycine-ortho-carb- 

 oxylic acid. These two products are obtained by the 

 electrolysis of sodium chloride. As, however, the chlorine 

 as it is first produced is not sufficiently pure, it is purified 

 by condensing it to the liquid condition. Attention has 

 been drawn to the details of the manufactunng process, 

 in order to show what a determined and powerful com- 

 petition the Indian indigo producer has to face. 



Synthetical indigo is being used in this country, but 

 there is a considerable difference of opinion as to 

 whether it is as easy to dye with the artificial as with the 

 natural product. Some dyers state that there is a diffi- 

 culty in obtaining the requisite bloom and that, therefore, 

 materials dyed with it have a flat or dead appearance ; 

 other operators seem to find no such difficulty. Practi- 

 cally the only drawback to materials dyed with indigo is 

 that the dye is inclined to rub. Some dyers say that 

 goods dyed with synthetical indigo rub more than when 

 dyed with the vegetable indigo. This, again, is denied by 

 others. There is also said to be a difficulty in reducing 

 synthetical indigo. In print-work synthetical indigo cer- 

 tainly appears to possess an advantage, owing to its fine 

 state of division and to the fact of its containing no 

 foreign matter which might scratch and injure the 

 rollers. Before natural indigo can be employed, it is 

 necessary to have it in an exceedingly fine slate of divi- 

 sion, and in order to ensure this it is usually ground in a 

 mill with water for several days. The artificial product, 

 on the other hand, is sent into the market as a very fine 

 powder or in the form of a paste. One drawback to 

 natural indigo is the varying amounts of indigoiin which 

 different samples contain. Artificial indigo contains not 

 only a very high percentage of indigotin, but practically 

 no foreign matter. 



Dr. Brunck is sanguine that the synthetical product 

 will shortly overcome all competition and drive the 

 natural product from the market ; and in his address, 

 with a disinterestedness which cannot but be admired, 

 advises the Government of India to ascertain in what 

 manner the land which has been employed for growing 

 indigo may be best cultivated. If the advice of Dr. 

 Brunck is taken, there will be no doubt as to the success 

 of the artificial indigo. .'Vs showing the vast import- 

 ance of the question to India, the following statistics are 

 given. In Northern Behar there are from 250,000 to 

 300,000 acres of land devoted to the cultivation of indigo, 



