May, 1923
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T h e Decolorizing Action of Bone Black’ By Paul M. Horton AUDUBON SUGAR SCHOOL,BATON ROUGE,LA.
T
H E complex subThe experimental wort of Patterson and Hall on bone black is reviewed. Nitrogenous substances extracted by sulfuric acid are stance known as animal or bone black not necessarily the active materials in bone black. Experimental is the product of the lowproof is submitted. temperature distillation of bones. It is of considerable technical importance and therefore has been submitted to much investigation relative to its composition and properNAME OF CHAR ties. This paper deals only with its ability to remove color Norite Darco from certain types of solutions. Supchar Kelp char Carbrox Bone char Purified bone char C . P. sucrose char
WORKOF PATTERSON AND HALL Nitrogen has long been recognized as a constant constituent of active bone char, and the fact that as the activity of a given char decreases with use the nitrogen content is diminished has led to many attempts to prove it to be the active constituent of the char. As early as 1865 Wallace2 suggested that the active body is a compound of carbon and nitrogen. P a t t e r ~ o n however, ,~ was the first to isolate a nitrogenous substance from bone char, which, according to his data, was even more active as a decolorizer than the char from which it was obtained. He stated, therefore, that the active principle of the char was comprised of the nitrogenous bodies present. Hall4 recently confirmed this conclusion. Patterson obtained the active substance by treating the purified bone char with about twenty times its weight of concentrated sulfuric acid, followed by filtration through asbestos and dilution of the filtrate with water. A brown to black gelatinous substance soon precipitated from the dilute solution, which was further purified by washing. It was shown by analysis to be a nitrogenous compound similar in composition to the cartilaginous substance of bones. Hall’s work consisted in the substitution of alundum for asbestos as the filter. Zerban5 has demonstrated that a more active char can be prepared from a mixture of sawdust and casein than can be obtained from the sawdust alone. This seems to support the work of Patterson. However, these chars were all of low power, and there was little conclusive evidence that nitrogenous matter played an important part in the increased decolorizing power. I n this instance such an assumption might lead to the conclusion that a char from sawdust mixed with casein could show a certain degree of activity, even though the raw sawdust was known to yield an inactive char. Furthermore, the activity might be expected to follow some simple function of the nitrogen content when the latter is present in small amounts. Neither of these conclusions is substantiated by the data published. There is no published record of an attempt to correlate the decolorizing power of a char and its nitrogen content. Furthermore, unless the data are confined to bone char-a char unique among chars-no relationship will probably be found. I n this laboratory carbon made from C . P. sucrose has been activated many times, simply by selective oxidation. 1 Presented before the Division of Sugar Chemistry at the Bard Meeting of the American Chemical Society, Birmingham, Ala., April 3 to 7, 1922. 2 Proc. Glasgow Phil. SOC., 6 (1865). 377. 3 J . SOC.Chem. I n d . , 32 (1903), 608. 4 THIS JOURNAL, 14 (1922), 18. 8 Louisiana State University, Bull. 167.
(See also the work of Bartell and Miller.‘) The analYSiS of a few typical commercial chars7 is inserted in further proof of this contention. Per cent Nitrogen 0.136 0.265 0.070 2.000 0.590 1,060 2.570 0.000
Decolorizing Power 1.00 0.99 1.01 0.50 0.95 0.30 0.46 0.82
Raw rice-bran carbon contains more nitrogen than the most active of the vegetable chars cited above, but it is absolutely inactive. The kelp char and sucrose char used in this series were not activated to the highest degree; therefore, the figures are not as convincing in these cases as they might be. If it is admitted that the extracted matter from bone black exhibits a certain degree of activity, it is not necessary to postulate that this material represents all, or even a large part, of the active substance of bone black. Certainly, the adsorptive capacity of the extractive would not be expected to exhibit a degree of activity equal to that of the char, since in the latter it is very uniformly distributed over a large surface of inert material, while in the extracted solution it is a more or less gelatinous coagulum. This contention cannot, however, be disproved, owing to the experimental difficulties encountered. For example, if the loss in capacity of the char exactly equaled that of the extract, sufficient proof would have been given that the extract represented the active constituent of the char. Patterson claims to have shown this. Tanners has expressed some doubt of this, however. I n view of the theory that decolorization is a specific surface effect, and that the char and the extract are radically different in structure, it is probable that Patterson’s work is erroneous in this respect also. Again, direct proof cannot be obtained since the residual char substance remaining after extraction is profoundly modified. It shows considerable solubility in water, the color is grayish instead of black, and it is soft and amorphous. The temperature of extraction, if varied, will not only change the amount but the nature of the extract obtained, as is shown later. Hence, it would be an error in principle to attempt a comparison of the char in the original to the char in the extracted form. I n a series of experiments on the production of an activated carbon by the action of sulfuric acid on sugar or molasses, it was found that the apparent activity of the char decreased upon prolonged washing with water. The char can be washed with water for about 3 hrs. and the runnings will be apparently neutral. However, upon boiling with water the filtrate will become acid again. This throws some light upon Patterson’s experiments, for even if his extract were a t first neutral, upon standing several hours sufficient acid J . A m Chem. SOC., 44 (1922), 1866. Analyses made b y J. L. Farr of the State Experiment Station of Louisiana. ( T H I S JOURNAL, 14 (1922), 19. 6
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is slowly dissolved from the extract to exhibit considerable bleaching effect upon the caramel test solution. The molasses char mentioned above became absolutely inactive upon boiling with dilute sodium hydroxide, or upon ignition to 400" C. Patterson's dried extract showed no decolorizing effect; hence, it is apparent that occluded acid will account for all the effects observed, as, if the acid is removed by neutralization, volatilization, or reduction (upon ignition the odor of SO2 is observed from chars made with sulfuric acid), the char becomes absolutely inactive. It should be mentioned in passing that all chars made by the action of sulfuric acid on organic matter are not inactive when neutral. The change in color of a molasses or caramel solution with change of acidity has been recognized for some time, and is mentioned in publications from this laboratory and by Turrentine and Tanner.* This fact, of course, explains the extraordinary activity sometimes exhibited by vegetable chars, as they are often washed with acid to remove soluble ash. The acid is then retained very tenaciously, even when the char is heated to 400" C. However, when the char is tested sufficient acid goes into solution to exert a considerable effect. Patterson and Hall mention the extreme difficulty encountered in washing the acid out of the precipitated matter from the acid extract of bone char. The precipitate tends to pass into a colloidal solution after a certain amount of dilution. It is apparent, therefore, that the treatment given the precipitate removed the acid only superficially. German and Traxlerg verify the well-known fact-in another connection, however-that it is impossible to wash all absorbed matter from a precipitate when treated on a Buchner funnel. It was found that when three drops of 0.1 N sulfuric acid were added to the caramel solution used in testing the extract approximately 25 per cent of the total color was discharged. The extreme importance of this one factor should now be apparent.
EXPERIMENTAL A large quantity of commercial granulated bone black was first ground to pass through an 80-mesh sieve, suspended in boiling water, and treated with portions of hydrochloric acid until no more gas was evolved. An excess of acid was avoided. The char was then filtered and washed thoroughly, then dried over night at 300' C. The treated char was blacker and more amorphous than the original material. Twenty grams of the char were then treated with 100 cc. of concentrated sulfuric acid, allowed to stand for 5 hrs. a t room temperature, and filtered. The filtration was first made with asbestos, as recommended by Patterson, then the filtrate passed through a dense alundum thimble, as recommended by Hall. The thimble removed a small amount of material from the filtrate through the asbestos, which was shown to be very fine particles of unchanged char. However, on account of the dense and viscous nature of the filter cake, it was found to wash very slowly. Consequently, a small filter of the Pukal type was used in all subsequent work, the cake being sucked dry and then scraped off into a beaker where it was mixed with fresh acid and again filtered. This procedure was repeated until the filtrate became clear. Washing with dilute acid offers no advantages. After the preliminary work was completed two series of experiments were made. I n the first, bone char was extracted with concentrated acid for 1 hr. a t the temperature of the water bath. In the second series, the extraction was made with concentrated acid a t room temperature for 3 9
J . A m . Chem. SOC.,44 (1922), 463.
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days. The filtration was made through a Pukal filter, the filtrates being treated identically in all cases-i. e., diluted with 5 volumes of water and washed by decantation until the precipitate began to pass into solution. The suspension was then dialyzed for 36 hrs. in running water at about 20'C., then for 6 hrs. in distilled water at 80" C. Collodion sacks were employed as the membrane. I n all cases the dialysate was shown to be free from acid by testing with barium chloride. The purified extract thus obtained from the hot acid extraction slowly flocculated upon standing a few hours, while that from the cold extraction remained in suspension for several days. I n fact, one specimen was observed for 3 wks., with only a small amount of sedimentation. The purified extracts were then washed into a liter flask and made to the mark with distilled water. Fifty cubic centimeters of this solution then represented 1 g. of char. One hundred cubic centimeters of each solution were evaporated on the water bath and dried at 110' C. to constant weight. The amount of substance extracted was thus found to average 9.1 per cent for the hot and 7.3 per cent for the cold extraction. The char showed a loss on ignition of 32.6 per cent. In order to test the extracts, a solution of 10 g. of caramelized sugar per liter was made and buffered according to the method of Tuxrentine and Tanner.s The solution showed no change in color upon adding a few drops of dilute acid of any kind. The solution upon dilution was also shown to follow Beer's law within the limits of the Klett colorimeter used. Fifty cubic centimeters of the extract and 50 cc. of the caramel solution were mixed and heated on the water bath for 1hr., and filtered with the use of a little kieselguhr. The comparison was made against the original caramel solution diluted with an equal volume of distilled water, heated, and filtered with kieselguhr.
RESULTS The extracts showed no decolorizing power whatever, provided the mixtures of bone char and sulfuric acid were carefully filtered. Sulfuric acid seems to cause the char to pass through a filter unless the pores are very fine, in which case the extract will be active.
CONCLUSION I n conclusion, it is suggested that bone char owes its power of removing color to the presence of active carbon, and that
the nitrogenous material serves as a reserve to supply fresh carbon upon reignition. This will explain why the char can be renewed by ignition only as long as it contains nitrogenous material, and why the latter disappears with continued use. This does not preclude the possibility, however, that protein matter may have an important influence upon the form assumed by the carbon upon ignition. I n general, it is assumed that the activity of a char from any source is due to the same form of amorphous carbon, produced by the low-temperature decomposition of vegetable or animal substances. Usually, the carbon surface is coated over by a layer of ash or hydrocarbons. The surface may then be exposed, or the char activated, by removal of this film. I n the case of sucrose or wood char this may be accomplished by selective oxidation; in the case of highly siliceous material such as rice-hull char the surface may be uncovered by boiling with sodium hydroxide; in the case of bone char the surface film is evidently soluble in water or dilute acids. This theory will be taken up further in subsequent publications from this department.
