Chapter 8

When Mr. Greene says that the relations between the physical properties of solids and liquids and their molecular composition can in no manner affect the laws of gases, nobody is likely to dissent; but the conclusion that their discussion is foreign to the question of the number of molecules in unit of volume does by no means follow. If the specific gravity of a solid or the weight of unit of volume represents a certain number of molecules, and is found to occupy two volumes in a compound of the solid with another solid, the number of molecules in one volume is reduced to one half. This I have shown to be the case in a number of compounds, and the decrease of the specific gravity with increase of the complexity of composition appears to be a general law, as may be concluded from the very low specific gravity of the most highly organized compounds, for instance the fatty bodies, the molecules of which, being composed of very many constituents, are of heavy weight; and likewise the compounds which occur in combination with water and without it, the simpler compound having invariably a greater specific gravity than the one combined with water; for instance:

BaH_2O_2 sp. gr. 4.495 " " + 8H_2O " 1.656 S_2H_2O_2 " 3.625 " " + 8H_2O " 1.396 FeSO_4 " 3.138 " + 7H_2O " 1.857

and so in every other case. This is now a recurrence of what takes place in gases, and proves the fallacy of the hypothesis; for if these compounds could be volatilized the vapor densities would necessarily vary in the inverse proportion of the degree of composition.

The reproach that Berthelot has been endeavoring for nearly a quarter of a century to hold back the progress of scientific chemistry, is a great and unjustifiable misrepresentation of the distinguished chemist and member of the Institute of France, who has done so much for thermo-chemistry, and the more unfortunate as it seems to serve only the purpose of a prelude to the following sentences: "But Mr. Vogel cannot claim, as can Mr. Berthelot, any real work or experiment, however roughly performed, suggested by the desire to prove the truth of his own views. Let him not, then, bring forth old and long since explained discrepancies, ... but when he will have discovered new or overlooked facts ... chemists will gladly listen." ... Mr. Greene is here no longer occupied to investigate whether what I have said concerning Avogadro's hypothesis is true or false, but with myself he has become personal, and in noticing his remarks my sole object is to contend against an error which is much prevalent. If, according to Mr. Greene, the real work of science consists in experimenting, and conclusions unsupported by our own experiments have no value, it does not appear for what purpose he has published his answer to my paper; an experiment of his, settling Marignac's uncertain results, would have justified the reliance he places on them. The ground he takes is utterly untenable. Experiments are necessary to establish facts; without them there could be no science, and the highest credit is due to those who perform successfully difficult or costly experiments. Experimenting is, however, not the aim and object of science, but the means to arrive at the truth; and discoveries derived from accumulated and generally accepted facts are not the less valuable on account of not having been derived from new and special experiment.

It is, further, far from true that the real work of science consists in experimenting; mental work is not less required, and the greatest results have not been obtained by experimenters, but by the mental labor of those who have, from the study of established facts, arrived at conclusions which the experimenters had failed to draw. This is naturally so, because a great generalization must explain all the facts involved, and can be derived only from their study; but the attention of the experimenter is necessarily absorbed by the special work he undertakes. I refer to the three greatest events in science: the discovery of the Copernican system, the three laws of Kepler, and Newton's law of gravitation, none of which is due to direct and special experimentation. Copernicus was an astronomer, but the discovery of his system is due chiefly to his study of the complications of the Ptolemaic system. Kepler is a memorable witness of what can be accomplished by skillful and persistent mental labor. "His discoveries were secrets extorted from nature by the most profound and laborious research." The discovery of his third law is said to have occupied him seventeen years. Newton's great discovery is likewise the result of mental labor; he was enabled to accomplish it by means of the laws of Kepler, the laws of falling bodies established by Galileo, and Picard's exact measurement of a degree of a meridian.

If, then, mental work is as indispensable as experimental, it is not less true that there are men more specially fitted for the one, others for the other, and the best interests of science will be served when experiments are made by those specially adapted, skillful, and favorably situated, and the possibly greatest number of men, able and willing to do mental work, engage in extracting from the accumulated treasures of experimental science all the results which they are capable to yield. Any truth discovered by this means is clear gain, and saves the waste of time, labor, and money spent in unnecessary experiment. Mr. Greene's zeal for experiment and depreciation of mental work would be in order, if ways and means were to be found to render the advancement of science as difficult and slow as possible; they are decidedly not in the interest of science, and can not have been inspired by a desire for its promotion.

As the evidence of the specific heats of the fallacy of Avogadro's hypothesis involves lengthy explanations, the subject is reserved for another paper.

San Francisco, Cal., May, 1881.

E. VOGEL.

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DYEING REDS WITH ARTIFICIAL ALIZARIN.

By M. MAURICE PRUD'HOMME.

Since several years, the methods of madder dyeing have undergone a complete revolution, the origin of which we will seek to point out. When artificial alizarin, thanks to the beautiful researches of Graebe and Liebermann, made its industrial appearance in 1869, it was soon found that the commercial product, though yielding beautiful purples, was incapable of producing brilliant reds (C. Koechlin). While admitting that the new product was identical with the alizarin extracted from madder, we were led to conclude that in order to produce fine Turkey reds, the coloring matters which accompany alizarin must play an important part. This was the idea propounded by Kuhlmann as far back as 1828 (_Soc. Ind. de Mulhouse_, 49, p. 86). According to the researches of MM. Schützenberger and Schiffert, the coloring matters of madder are alizarin, purpurin, pseudopurpurin, purpuroxanthin, and an orange matter, which M. Rosenstiehl considers identical with hydrated purpurin. Subsequently, there have been added to the list an orange body, purpuroxantho-carbonic acid of Schunck and Roemer, identical with the munjistin found by Stenhouse in the madder of India. It was known that purpuroxanthin does not dye; that pseudopurpurin is very easily transformed into purpurin, and the uncertainty which was felt concerning hydrated purpurin left room merely for the hypothesis that Turkey-red is obtained by the concurrent action of alizarin and purpurin. In the meantime, the manufacture of artificial alizarin became extended, and a compound was sold as "alizarin for reds." It is now known, thanks to the researches of Perkin, Schunck, Roemer, Graebe, and Liebermann, that in the manufacture of artificial alizarin there are produced three distinct coloring matters--alizarin, iso or anthrapurpurin, and flavopurpurin, the two latter being isomers of purpurin. We may remark that purpurin has not been obtained by direct synthesis. M. de Lalande has produced it by the oxidation of alizarin. Alizarin is derived from monosulphanthraquinonic acid, on melting with the hydrate of potassa or soda. It is a dioxyanthraquinone.

Anthrapurpurin and flavopurpurin are obtained from two isomeric disulphanthraquinonic acids, improperly named isoanthraflavic and anthraflavic acids, which are converted into anthrapurpurin and flavopurpurin by a more profound action of potassa. These two bodies are trioxyanthraquinones.

We call to mind that alizarin dyes reds of a violet tone, free from yellow; roses with a blue cast and beautiful purples. Anthrapurpurin and flavopurpurin differ little from each other, though the shades dyed with the latter are more yellow. The reds produced with these coloring matters have a very bright yellowish reflection, but the roses are too yellow and the purples incline to a dull gray.

Experience with the madder colors shows that a mixture of alizarin and purpurin yields the most beautiful roses in the steam style, but it is not the same in dyeing, where the roses got with fleur de garance have never been equaled.

"Alizarins for reds" all contain more or less of alizarin properly so-called, from 1 to 10 per cent., along with anthrapurpurin and flavopurpurin. This proportion does not affect the tone of the reds obtained further than by preventing them by having too yellow a tone.

The first use of the alizarins for reds was for application of styles, that is colors containing at once the mordant and the coloring matter and fixed upon the cloth by the action of steam. Good steam-reds were easily obtained by using receipts originally designed for extracts of madder (mixtures of alizarin and purpurin). On the other hand, the first attempts at dyeing red grounds and red pieces were not successful. The custom of dyeing up to a brown with fleur and then lightening the shade by a succession of soapings and cleanings had much to do with this failure. Goods, mordanted with alumina and dyed with alizarin for reds up to saturation, never reach the brown tone given by fleur or garancin. This tone is due in great part to the presence of fawn colored matters, which the cleanings and soapings served to destroy or remove. The same operations have also another end--to transform the purpurin into its hydrate, which is brighter and more solid. The shade, in a word, loses in depth and gains in brightness. With alizarins for reds, the case is quite different; they contain no impurities to remove and no bodies which may gain brightness in consequence of chemical changes under the influence of the clearings and soapings. These have only one result, in addition to the formation of a lake of fatty acid, that is to make the shades lose in intensity. The method of subjecting reds got up with alizarin to the same treatment as madder-reds was faulty.

There appeared next a method of dyeing bases upon different principles. The work of M. Schützenberger (1864) speaks of the use of sulpho-conjugated fatty acids for the fixation of aniline colors. In England, for a number of years, dyed-reds had been padded in soap-baths and afterwards steamed to brighten the red. In 1867, Braun and Cordier, of Rouen, exhibited Turkey reds dyed in five days. The pieces were passed through aluminate of soda at 18° B., then through ammonium chloride, washed, dyed with garancin, taken through an oil-bath, dried and steamed for an hour, and were finally cleared in the ordinary manner for Turkey-reds. The oil-bath was prepared by treating olive-oil with nitric acid. This preparation, invented by Hirn, was applied since 1846 by Braun (Braun and Cordier). Since 1849, Gros, Roman, and Marozeau, of Wesserling, printed fine furniture styles by block upon pieces previously taken through sulpholeic acid. When the pieces were steamed and washed the reds and roses were superior to the old dyed reds and roses produced at the cost of many sourings and soapings. Certain makers of aniline colors sold mixtures ready prepared for printing which were known to contain sulpholeic acids. There was thus an idea in the air that sulpholeic acid, under the influence of steam, formed brilliant and solid lakes with coloring matters. These facts detract in nothing from the merit of M. Horace Koechlin, who combined these scattered data into a true discovery. The original process may be summed up under the following heads: Printing or padding with an aluminous mordant, which is fixed and cleaned in the usual manner; dyeing in alizarin for reds with addition of calcium acetate; padding in sulpholeic acid and drying; steaming and soaping. The process was next introduced into England, whence it returned with the following modifications; in place of olive-oil or oleic acid, castor oil was used, as cheaper, and the number of operations was reduced. Castor oil, modified by sulphuric acid, can be introduced at once into the dye-beck, so that the fixation of the coloring matter as the lake of a fatty acid is effected in a single operation. The dyeing was then followed by steaming and soaping.

For red on white grounds and for red grounds, a mordant of red liquor at 5° to 6° B. is printed on, with a little salt of tin or nitro-muriate of tin. It is fixed by oxidation at 30° to 35° C., and dunged with cow-dung and chalk. The pieces are then dyed with 1 part alizarin for reds at 10 per cent., ¼ to ½ oil for reds (containing 50 per cent.), 1-6th part acetate of lime at 15° B., giving an hour at 70° and half an hour at the same heat. Wash, pad in oil (50 to 100 grms. per liter of water), dry on the drum, or better, in the hot flue, and steam for three-quarters to an hour and a half. The padding in oil is needless, if sufficient oil has been used in dyeing, and the pieces may be at once dried and steamed. Wash and soap for three-quarters of an hour at 60°. Give a second soaping if necessary. If there is no fear of soiling the whites, dye at a boil for the last half-hour, which is in part equal to steaming.

Red pieces and yarns may be dyed by the process just given for red grounds; or, prepare in neutral red oil, in the proportion of 150 grms. per liter of water for pieces and 15 kilos for 100 kilos of yarns. For pieces, pad with an ordinary machine with rollers covered with calico. Dry the pieces in the drum, and the yarn in the stove. Steam three-quarters of an hour at 1½ atmosphere. Mordant in pyrolignite of alumina at 10° B., and wash thoroughly. Dye for an hour at 70°, and half an hour longer at the same heat, using for 100 kilos of cloth or yarn 20 kilos alizarin at 10 per cent., 10 kilos acetate of lime at 18° B., and 5 kilos sulpholeic acid. Steam for an hour. Soap for a longer or shorter time, with or without the addition of soda crystals. There may be added to the aluminous mordant a little salt of tin to raise the tone. Lastly, aluminate of soda may be used as a mordant in place of red liquor or sulphate of alumina.

Certain firms employ a so-called continuous process. The pieces are passed into a cistern 6 meters long and fitted with rollers. This dye-bath contains, from 3 to 5 grms. of alizarin per liter of water, and is heated to 98°. The pieces take 5 minutes to traverse this cistern, and, owing to the high temperature and the concentration of the dye liquor, they come out perfectly dyed. Two pieces may even be passed through at once, one above the other. As the dye-bath becomes exhausted, it must be recruited from time to time with fresh quantities of alizarin. The great advantage of this method is that it economizes not merely time but coloring matter.

The quantity of acetate of lime to be employed in dyeing varies with the composition of the mordant and with that of the water. Schlumberger has shown that Turkey-red contains 4 molecules of alumina to 3 of lime. Rosenstiehl has shown that alumina mordants are properly saturated if two equivalents of lime are used for each equivalent of alizarin, if the dyeing is done without oil. These figures require to be modified when the oil is put into the dye beck, as it precipitates the lime. Acetate of lime at 15° B., obtained by saturating acetic acid with chalk and adding a slight excess of acetic acid, contains about ¼ mol. acetate of lime.--_Bulletin de la Société Chimique de Paris._

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