I080
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
Now, if the buyer does not boil his dye up a t a sufficiently high concentration he may not bring about ‘a complete conversion of the calcium salt into the sodium salt and the calcium salt may not enter into the dyeing process a t all. I can remeniber a lot of dyestuff that was variously estimated at all the way from 0 . K. to 50 per cent weak according to the locality and method of dyeing. A practice which prevails in some large laboratories doing much work of this kind sometimes leads t o incorrect results. I n such laboratories it is customary to keep a girl or boy steadily employed in winding off and weighing to a definite weight, skeins of yarn for use in dyeing, these skeins being stored in such a way that a skein wound and weighed a t one time may be dyed against a skein wound and weighed some time previously. Now as wool and cotton are both hygroscopic, it is evident that the moisture content of woolen skeins may vary considerably within a few days. Hence, unless some control is maintained, a considerable error may be introduced here. It has been Found in our laboratory that a skein exposed to the air will vary by as much as 8 per cent within a few days. Our practice is to open up the large skeins as received and expose them to the atmosphere of the winding room for 24 hours before winding off the small skeins. Then instead of a metal weight a standard skein of the same quality is used as a counterpoise. Working in this way we find that our skeins maintain a constant weight of dry material. As a further precaution, however, each day’s winding is kept separate, and in a trial, only skeins wound and weighed a t the same time are taken. The colorist must also asswe himself that his material contains nothing that will interfere in any way with his dyeing. I have found it almost impossible to obtain woolen piece goods from any source, that does not a t times contain either sulfuric or sulfurous acids. I n some cases either of these acids might vitiate conclusions drawn from a test. -4common practice when very accurate results are wished, particularly in the estimation of yellows of clear shade, is the addition of small amounts of either a red or a blue. This expedient is frequently resorted to without proper consideration being given to the magnitude of the error that may be introduced in this way. These additions of a second color are generally made with the view of catching very slight differences. I have seen such 5 cc. additions made, the measuring being done in a 2 5 cc. cylinder. I doubt if anything was added to the accuracy of the final estimation of strength by such procedure. But when all precautions have been taken and all possibilities considered, there remains one cause of disagreement that is wellnigh insuperable. All findings based on comparative dye trials depend for their correctness on the judgment of the observer. I have frequently tested the accuracy with which an experienced dyer can detect a strength difference and have found that the average experienced man will, nine times out of ten, detect a difference of 3 per cent, but will not certainly detect a smaller difference. Now this means that in standardizing i t is easily possible that deliveries will sometimes be 3 per cent stronger and sometimes 3 per cent weaker than the standard. Unless the buyer has the exact standard used by the seller he may occasionally, if he has taken for his standard a 3 per cent stronger delivery, find lots that show weakness, and he will, of course, claim a I O or 15 per cent difference. This is t o emphasize the necessity of seeing to it that buyer and seller operate with exactly the same standard and that such standard samples are carefully preserved. One other point in the estimation of strength from comparative dyeings must always be borne in mind, and that is the Pallibility of human judgment. Let anyone divide a skein of colored yarn into two equal portions and mark one portion A and the other B, then hand them to anyone with the remark that B is a trifle weaker. In the majority of cases you will find that
Vol.
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he will agree with you. Unconsciously the man working on dye trials will be influenced by his prepossessions and will frequently honestly see a difference where none exists simply because he expects to find it or has been told that it does exist. My feeling is that the buyer should make no claim except for differences that are clearly apparent to a trained eye, and on LIe other hand when such differences are apparent the seller should unhesitatingly allow the claim. NATIONAL ANILINEAND BUFFALO,
CHEMICAL COMPANY
N e w YORE
THE PLACE OF PHYSICAL CHEMISTRY IN DYESTUFF RESEARCH By E. K. STRACHAN
The success of the dyestuff industry, perhaps more than that of any other industry, is dependent on chemical research. It is more dependent upon research than on manufacturing secrets, or patent laws, or tariff protection. Chemical research is the keystone of the entire industry. On account of the important position which it occupies, the research organization of the American dyestuff industry should receive an exceedingly careful scrutiny. No pains shoiild be spared to make our research organizations as comprehensive in their scope and as thoroughly adapted to their purpose as possible. It is as true of research as of any other branch of manufacturing, that a complete and well-developed organization is more effective in the long run, than is individual brilliancy. It is almost a commonplace to state that such an organization should include physical chemistry as one of its departments. There is hardly a chemical problem that can be mentioned but someone will remark, “Let us see what the physical chemist has t o say about this,” and I am sure that a good many of our physical chemists would he a t a loss to say, off-hand, precisely what they could do to assist in dyestuff research. On the other hand, I know from experience that a very large proportion of the dyestuff chemists would feel that it was futile t o attempt to apply physicochemical methods to their work. It is my purpose in this talk to illustrate a few of the uses of physical chemistry in dyestuff research, in order that any man conducting this kind of research will not neglect such a valuable tool. I also desire to turn the attention of physical chemists themselves to a commercial use of their particular methods. Since the larger part of the problems arising a t present have to do with the preparation of dyestuff intermediates, these remarks might apply equally well t o any other industry manufacturing organic chemicals. For our present purposes, physical chemistry may be regarded principally as an attitude of mind or method of attack, rather than a separate body of knowledge. It is true that this branch of chemistry does possess a small body of knowledge not common to other branches of chemistry, but this is its least important aspect. .4nd indeed, the larger part of the work of the physical chemist connected with dyestuff research or in any other organization dealing with organic chemicals will be the contribution of his attitude of mind and of his methods of study to the discussion of any problem a t hand. It is my intention t o suggest a few particular uses of physical chemistry and to illustrate them by examples which have occurred in my own laboratory during the past few years. There is nothing strikingly original in any of these methods; most of them have been known for a long time. The function of the physical chemist has been to know when i t is profitable to apply various methods, to devise technique and equipment to carry them out successfully, and to systematize all physical chemical methods in use. As illustrations I have chosen t o mention the use of physical constants in analytical methods, physicochemical methods applied t o a few plant processes, and the contribntions of the physical chemist to the chemical engineer.
Kov., 1919
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
I n any chemical processes in which a small amount of impurities may render the products worthless, the analytical control of materials and procedures is highly important. Indeed, a comparatively small amount of foreign substances in some intermediates may completely ruin the shade of the finished dye. I n other cases, only a small percentage of some material that should not be present will decrease the weight yield of product enormously. This is an important consideration in dealing with high-pr iced materials. One of the very important functions of the physical chemist is that of establishing criterions of purity.
0
%
CARBAZOLE
A substance may be considered pure only when no method of fractionation will cause any change in any of its physical properties, that is, a pure substance may be fractionated by any means whatever that can be used and all of its fractions will have the same physical properties. Organic chemists for a long time have used the melting point as a criterion of purity. They have also employed the density, refractive index, solubility, and a number of other properties to a less extent for this same purpose. It is interesting to note, however, that the melting point is not always a sure criterion of purity. I am exhibiting in Fig. I a curve showing the melting point of mixtures of anthracene and carbazol. You will note from this curve that as much as 15 per cent carbazol may be present in anthracene without affecting the melting point by more than I ', and indeed a mixture containing 15 per cent carbazole has exactly the same melting point as pure anthracene. In such case we must use a different physical property as a criterion of purity. For this particular system the solubility will serve t o differentiate pure anthracene from anthracene mixed with carbazol. My purpose in presenting this curve is to show the necessity of knowing the melting point curve over all, or nearly all, of i M
20
M
Recently one of our chemists attempted to follow the course
of a certain distillation by measuring the melting point of the distillate. Much to his surprise the melting point appeared to remain constant while the bulk of the material distilled. Apparently distillation was not separating the components. A
io81
determination of the melting point curve of the system, which is shown in Fig. 2 , revealed the difficulty. Another physical constant, of course, was used, namely, the density. These remarks on physical properties as criterions of purity verge very closely on the use of physical properties as analytical methods. For analytical purposes, physical properties may be classified as one-sided properties and common properties. Optical rotation and color are both examples of what I mean by onesided properties, that is, they are properties possessed by only one component of a mixture. It is quite easy to determine the amount of an optically active substance present in its solution in an optically inactive solvent by well-known polariscopic methods. Similarly, the concentration of a colored substance in a colorless solvent is easily determined by the common colorimetric methods. On the other hand, the common properties are properties which are possessed in common by all components of the mixture, such as melting points, density, refractive indices, and many others. The use of these latter as analytical methods depends upon the knowledge that we have of a definite and limited number of components in the system. For instance, we must know that the system is binary, and contains nothing but) its two components, or ternary and contains nothing but its three components, and so on. It is quite easy to see this from a mathematical standpoint. I n a binary system we have two variables, namely, the per cent of each component. Two equations are therefore necessary to fix the value of the two variables. One of our equations for a binary system is that the sum of the percentages of the two components is 100; the other equation is that some particular physical property is a function of the amount of each component present. Ordinarily
we plot a curve from experimental data showing the change in the chosen physical property with the composition of the mixture. This, of course, is the way that the curves already shown were obtained. The choice of the particular physical property to be used in the analysis of a given system depends upon the characteristics of the system; for example, the composition of a mixture of 0- and p-nitrochlorbenzol can be determined very easily from its melting-point curve, which is shown in Fig. 3 . The upper curve represents the melting point of a mixture of pure, dry 0- and 9-nitrochlorbenzol. This was used for a time in determining the composition of the mixture until we reealled that the product we were analyzing was not dry but was saturated with water, whereupon the lower curve was constructed for the same substances saturated with water. This curve iIlustretes also the necessity of knowing precisely how many Components are present in the mixture. On the other hand, a melting-point curve would be of little use for the analysis of $-bofuidine containing small amounts of o-toluidine since the melting point of p-toluidine is about 2 1 ' below aero. Specific gravity
THE JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
I082
has been tried for this purpose, but owing to the fact that 0 . 5 per cent of o-toluidine causes a change of only 0.01 per c2nt in the specific gravity, the method is not very accurate. Further work should be done on this point.
Vol.
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of the mixture can be read off the curve. By measuring the melting point to within I' and the density to within 0.001 the composition can be determined within I per cent. This method yields good results in the laboratory. As far as I know it does not appear anywhere in the literature. Physicochemical methods can afford short cuts in the solution of a number of plant prohlems that otherwise could be solved only by the laborious method of cut and try. The distillation of aniline water, commonly known as oil water, is an interesting example. This is the aqueous portion of the distillate resulting from the steam distillation of aniline. It contains ahout 3.5 per cent of dissolved aniline which is recovered by distillation-scalping, as it is called. The aim of this process is to distil as large a proportion of aniline as possible and as little of the water. Should it he done under vacuum or atmospheric pressure? The vapor-pressure curves of aniline and water are shown in Fig. 5 . The proper conditions for distillation will
LE
PXQ.SPECIFIC GRAVITYAND FREEZING POINTSOF
THE
SYSTEM OR
O-NITRANISOL, O-NITROPHBNOI. AND 0-NITROCHLORBENZOL
There are quite a number of physical properties that have up to the present been very little used for analytical methods or as criterions of purity. These offer considerable promise and should by all means be tried. Among them are dielectric constant, magnetic susceptibility, electric birefringence, and magnetic rotation. For the same reason that the measurement of one physical property is necessary for the analysis of a binary system, it follows that the measurement of two physical properties is necessary for the analysis of a ternary system by purely physical means. Quite a few ternary systems can be analyzed by the removal of one component whereupon they become binary and the binary methods can be used. A mixture of hydrazobenzol, azobenzol, and azoxybenzol is typical of this situation.
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OF M f R C u R y
The hydrazobenzol can be removed by treating the system with hydrochloric acid which rearranges it to soluble benzidine hydrochloride. The mixture of azobenzol and azoxybenzol can then be filtered off and their ratio determined by the melting point of the mixture. On the other hand, it is sometimes easier and quicker to measure two physical constants than to attempt any separation. Fig. 4 shows both the melting point and specific gravity of the system o-nitrochlorbenzol, o-nitranisol, and o-nitrophenol plotted as functions of the composition. By measuring both melting point and density, the composition
I ArffOSP#PRt
DIFfCRENT T€MP€R4GUR€S
be those under which the ratio of the vapor pressure of aniline to that of water is the highest. Fig. 6 shows the change of this ratio with the temperature. Since the boiling point rises with increasing pressure, i t also shows the change of this ratio with increasing pressure. The ratio of aniline is much higher a t atmospheric pressure than in vacuum, but not enough higher under two atmospheres to warrant distilling under pressure. Experimental results are in accord with this conclusion. On the other hand, the vapor pressures of o- and p-nitrochlorbenzol are such that their ratio is constant a t all temperatures and, therefore, as far as any separation by distillation is concerned, the pressure is of no importance. The freezing-point curve affords a perfectly definite guide in the separation of a pure substance from a mixture by crystallization. T o obtain a maximum yield the mixture should be cooled to a temperature as near the eutectic as possible. But in order to avoid crystallization of the other components, the process should be so arranged that the mixture will not cool quite to the eutectic point until after it has been centrifuged or filtered. The curves of Fig. 7, which show the solubility of benzidine hydrochloride in hydrochloric acid, indicate a point of maximum solubility. The solubility in pure water is 4 per cent and in 0.2 normal acid 8 per cent. This is of considerable importance
N o v . , 1919
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
in view of the cost of wooden vats and the number of such vats required for large-scale production. By choice of suitable acid Concentration the vat space may be cut in half. On the other hand, too much acid renders the solution of the hydrochloride very difficult. 5
/4 IS
iz i/
9
28 $ 7 :6 $5
4
3 2 I 0
NOLS. ACID PER L I T E R
As business conditions approach more and more to the normal, efficiency of processes must he more closely watched. Here is one field where a physicochemical study of the mechanism, velocity, and ultimate equilibrium of all reactions is absolutely
I 083
essential. Thorough physicochemical study can do more toward the determination of maximum yields and quality of the product than +ny other line of work. The time and equipment required to make these physicochemical measurements is frequently overestimated. This has caused some chemists to believe that it is quicker and easier to settle these matters by actual trial in the laboratory or plant. Such a view is incorrect, for the vapor pressures, melting points, and similar physical properties which I have discussed, require no more time or skill than most of the operations of a routine analytical laboratory. We have trained intelligent boys and girls to employ standardized methods for the determination of those physical properties which are most in demand. A complete vapor-pressure curve may be determined in a single day. The data obtained by use of our apparatus and technique have been compared with the results of some of the best experimenters on well-known substances and we agree with them as well as they do with each other. A complete melting-point curve can be measured in two days with an error not exceeding 0.1’. I doubt if the information which can be deduced from these physical daia could be obtained by cut and try experimentation in anywhere near this time. Of course, none of these scientific shortcuts can supplant actual laboratory or plant trial as ultimate proof of a method. They do, however, frequently replace much time-consuming experimentation, NATIONAL ANILINE AND CHEMICAL COMPANY BUFFALO,N E W Y O R K
BIBLIOGRAPHY OF THE. LITERATURE OF ORGANIC MERCURIALS 1
-I
B y FRANK C. WHITMORE, University of Minnesota, Minneapolis, Minnesota
Received July 21, 1,919
The interest in organic mercury compounds has been steadily increasing during the last few years. This is largely due to the growing feeling among medical men that the much-lauded organic arsenicals are not coming up to expectations in the treatment o f syphilis. This feeling has led to a rather intensive search for organic mercury compounds which shall lack the toxic effect of the mercuric ion but shall retain the marked spirillocidic properties of the element. The publication of this bibliography was prompted by the effort of Dr. A. S. Loevenhart, of the University of Wisconsin, to enlist the efforts of a large number of American organic chemists in the making of new organic mercurials to be tested for possible chemotherapeutic uses. I t is hoped that the bibliography will be helpful to chemists who may becom? interested in this field. The chemistry of organic mercurials has nowhere been satisfactorily summarized or reviewed as has that of the organic: arsenic compounds. A good grasp of the chemistry of the known organic mercurials can only be obtained by mastering almost all of the individual papers. The beginner in the field will be helped by first reading a few articles which contain most of the typical reactions which occur in many of the other papers. Otto1 gives a thorough treatment of the chemistry of merciiry diphenyl. The reactions of this substance are typical of most compounds in which both valences of the mercury are attached to carbon. Pesci2 reviews most of his work published in Gazzetta chimica italiana on the introduction of mercury atoms and groups into aromatic amines. Dimroths studies “mercuration” as a general reaction of all aromatic compounds, as general as nitration or sulfonation. Brieger and * A n n , 154 (1870). 93 Z norg Chcm , AS (1897), 208 a Bet’., 8 1 (1898), 2154, S A (1899), 758; 86 (1902), 2032, 2853.
Schulemannl give a good brief history of organic mercurials and make an exhaustive study of new mercury compounds of naphthalene derivatives, chiefly on the substances which are commercially available as dye intermediates. It will be noted that all four of the articles recommended deal with aromatic compounds. This choice was made because the chemistry of the aromatic mercury compounds is much more definitely known and the substances likely to be of chemotherapeutic value are mainly aromatic. Notable exceptions to this rule are the complex mercury thio compounds which have been recently studied by a number of the French chemists. The first part of the bibliography contains a systematic list of the parent substances from which the organic mereitrials are actually prepared or may theoretically be derived. These parent substances are arranged in the order used in the third edition of Beilstein. By comparing the table of contents in the front of a volume of Beilstein with the corresponding part of the bibliography it is possible to tell a t a glance what classes of compounds are not represented by organic mercurials. It will be noted that the gaps are many and extensive. Compounds to fill these gaps should be made and thoroughly tested for their pharmacological properties. Of course their purely chemical properties should not be neglected. Too much of the modern work on organic mercurials has aimed a t immediate usefulness. The result of this tendency is that we do not know nearly as much of the chemistry of organic mercury as we should, considering the great number of compounds which have been prepared. The second part of the bibliography consists of a series of references illustrating the important reactions of mercury compounds having either one or both valences attached to carbon. J . pro& Chcm., [2], 89 (1914), 97.
