230 



process. But a still more important fact remains, that no print- 

 ing process exists in which indigo can be used in combination 

 with other colours in the ordinary way, or without requiring 

 some special mode of fixing after printing. Hence it is clear 

 that the weak points of natural indigo lie in the absence of any 

 good process for utilising the whole of its colouring matter, and 

 in the impossibility, or at any rate great difficulty, of employing 

 it in the ordinary madder styles of calico printing. Such were 

 the reasons which induced the patentees to believe that altliough 

 the artificial dye cannot be made at a price to compete with 

 natural indigo for use in the ordinary dye-beck, it can even now 

 be very lai-gely used for styles to which the ordinary dye-stuff is 

 inapplicable. 



To begin with, Baeyer employed (Patent 1 1 1 7) grape sugar 

 as a reducing agent. The reduction in this case does not take 

 place in the cold, and even on long standing only small traces 

 of indigo are formed, but if heated to 70° or upwards the change 

 takes place. Unfortunately this production of indigo-blue is rapidly 

 followed by its reduction to indigo-white, and it is somewhat 

 difficult in practice to stop the reaction at the right m^mient. 

 But Dr. Caro of Mannheim found that sodium xanthate is free 

 from many of the objections inherent to the glucose'reduction 

 process, inasmuch as the reaction then goes on in the cold. 

 Moreover, he finds that thei red isomeride of indigo-blue, 

 Indirubin, which possesses a splendid red colour, but has 

 little or no tinctorial power, is produced in less quantity in this 

 case than when glucose is employed. On this cloth, alumina 

 and iron mordants may be printed, and this afterwards dyed in 

 alizarine, &c. , or this colouring matter may also be printed on 

 the cloth and the colour fixed by moderate steaming without 

 damage to the indigoblue. This process is now in actual use by 

 printeis both in Kngland and on the Continent, so that, thanks 

 especially to the talent and energy of Dr. Caro, Bayer's dis- 

 covery has been practically applied within the short space of 

 twelve months of its conception. Operations on a manufactur- 

 ing scale have been successfully carried on in the Baden Suda 

 and Aniline Works at Ludwigshafen for the last two months, and 

 the directors see no reason why they should not be able to supply 

 any demand, however great, which may be made for ortho-nitro- 

 phenyl-propiolic acid. 



The proper way of looking' at this question at present is, 

 therefore, to consider ortho-nilro-phenyl-propiolic ac d and indigo 

 as two distinct products not comparable v^ ith each other, in.as- 

 much as the one can be put to uses for which the other is un- 

 fitted, and there is surely scope enough for both. Still, looking 

 at the improvements which will every day be made in the 

 manufacturing details, he must be a bold man who would assert 

 the impossibility of competition with indigo in all its applications. 

 For we must remember that we are only at the beginning of these 

 researches in the indigo field. Baeyer and other workers will 

 not stay their hands, and possibly other colouring matters of 

 equal intensity and of equal stability to indigo may be obtained 

 from other as yet unknown or unrecognised sources, and it is 

 not improbable that these may turn out to be more formidable 

 competitors in the race with natural indigo than ortho-nitro- 

 phenyl-propiolic acid. 



Looking at this question of the possible competition of 

 artificial with the natural indigo from another point of view, 

 it must, on the other, hand, be borne in mind that the present 

 mode of manufacturing indigo from the plant is extremely rude 

 and imperfect, and that by an improved and more careful carry- 

 ing out of the process, great saving in colouring matter may be 

 effected, so that it may prove possible to produce a purer article 

 at a lower price, and thus to counterbalance the production of 

 the artificial m iterial. 



The potential importance, from a purely commercial point of 

 view, of the manufacture, may be judged of by reference to the 

 following statistics, showing that the annual value of the world's 

 growth of indigo is no less than four millions sterlmg. 



How far the artificial will drive out the natural colouring 

 matter from the market cannot, as has been said, be foreseen. 

 It is interesting, as the only instance of the kind on record, 

 to cast a glance at the history of the production of the first of 

 the artificial vegetable colouring matter-, alizarin. In this case 

 the increase in the quantity produced since its discovery in 1S69 

 has been enormous, such indeed that the artificial colour has now 

 entirely superseded the natural one, to the almost omplet- aini- 

 hilation of the growth of madder-root. It appears that » hilst for 

 the ten years immediately preceding 1869 the avera^ie value of the 

 annual imports of madder-root was over one million sterling, 



NATURE [y«/v7, 1881 



Estimated Yearly Average of the Production of Indigo in the 

 World, taken from the Total Crop for a Period of Ten Years. 



the imports of the same material during last year ( 1S80) amounted 

 only to 24,000/., the whole difference being made up by the 

 introduction of artificial alizarin. In 1S68, no less a quantity 

 than 60,000 tons of madder-root were sent into the market, this 

 containing 600,000 kilos of pure natural alizarin. But in ten 

 years later a quantity of artificial alizarin more than equal to the 

 above amount was sent out from the various chemical factories. 

 So that in ten years the artificial production had overtaken the 

 natural growth, and the 3 or 400,000 acres of land which had 

 hitherto been used for the growth of madder, can henceforward 

 be better employed in growing corn or other articles of food. 

 According to returns, for which the speaker had to thank Mr. 

 Perkin, the estimated growth of madder in the world previous 

 to 1869 was 90,000 tons, of the average value of 45/. per ton, 

 representing a total of 4,050,000/. 



Last year (iSSo) the estimated production of the artificial 

 colouring matter was 14,000 tons, but this contains only 10 per 

 cent, of pure alizarin. Reckoning i ton of the artificial colour- 

 ing matter as equal to 9 tons of madder, the whole artificial 

 product is equivalent to 126,000 tons of madder. The present 

 value of these 14,000 tons of alizarin paste, at 122/. per ton, is 

 1,568,000/. That of 126,000 tonsofmadderat 45/. is 5,670,000/., 

 or a saving is effected by the use of alizarin of considerably over 

 four millions sterling. In other words, we get our alizarin dye- 

 ing done now for less than one-third of the price which we had 

 to pay to have it done with madder. 



To Englishmen it is a somewhat mortifying reflection, that 

 whilst the raw materials from which all these coal-tar colours 

 are made are produced in our country, the fini-hed and valuable 

 colours are nearly all manufactured in Germany. The crude and 

 inexpensive materials are, therefore, exported by us abroad, to 

 he converted into colours having many hundred times the value, 

 and these expensive colours have again to be bought by English 

 dyers and calico-printers for use in our staple industries. The 

 total annual value of manufactured coal-tar colours amounts to 

 about three and a half millions ; and as England, though furnish- 

 ing all the raw material, makes herself only a small fraction of 

 this quantity, but uses a large fraction, it is clear that she loses 

 the profit on the manufacture. The causes of this fact, which we 

 must acknowledge, viz., that Germany has driv> n England out of 

 the field in this important branch of chemical manufacture, are 

 probably various. In the first jilace, there is no doubt that much 

 of the German success is due to the long-continued attention 

 which their numerous universities have paid to the cultivation 

 of Organic Chemistry as a pure science. For this is carried out 

 with a degree of completeness, and to an extent, to which we in 

 England are as yet strangers. Secondly, much again is to be 

 attributed to the far more general recognition amongst German 

 than amongst English men of business of the value, from a 

 merely mercantile point of view, of high scientific training. In 

 proof of this it may be mentioned that each of two of the 

 largest German colour works employs no less a number than 

 from twenty-five to thirty highly-educated scientific chemists, 

 at salaries varying from 250/. to 5 or 600/. per annum. A third 

 cause which doubtless exerts a great influence in this matter is 

 the English law of patents. This, in the special case of colour- 

 ing matters at least, offers no protection to English patentees 

 against foreign infringement, for when these colours are ohce on 

 the goods they cannot be identified. Foreign infringers can 

 thus lower the price so that only the pateniee, if skilful, can 

 compete against them, and no English licencees of the patent 



