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THE JOURNAL
OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
Vol. 13, No. 11
keeping it exposed to air when its pH value is greater than 10 apparently prevents its precipitation when brought to 3; all such liquors remained brilliantly clear. The addition of a great excess of acid, however, caused all liquors to precipitate, while any precipitate could be completely redissolved by the addition of sufficient alkali. Another interesting fact is that the liquors exposed to air when their pH values lay between 8 and 9 gave much trouble with the hydrogen electrode. After bubbling hydrogen through them for only a few minutes, the voltage would fall rapidly towards zero. Even when brought to a pH value of 3.0, the liquors still gave this trouble and we had to check the results by meane of indicators. No such trouble was encountered with liquors exposed to air a t pH values below 7 or above 10. Apparently pH = 9 is a critical point in the oxidation of tan liquors. It may prove valuable to make much more extended studies of the changes going on at this point. EFFECT UPON LEATHER The changes in color of the tan liquors parallel in a rough way the changes in color imparted to hide. A hide tanned in a liquor having a high pH value not only comes from the liquor very dark in color, but this color continues to darken upon exposure to air. SUMMARY The color value of a tan liquor depends upon its hydrogenion concentration when used. A change in pH value produces a change in color of both liquor and leather. Tan liquors change in color like indicators with change in pH value, but over a range from 3 to 12. This change in color is completely reversible, if the liquors are not long exposed to air. Liquors exposed to air continue to darken in color, the more so the higher the pH value, but this change is not reversed by lowering the pH value. Liquors exposed to air a t pH values of about,9 give bulky precipitates when their pH values a,re brought to 3, and such liquors tend to poison the hydrogen electrode.
5 6 7 a g i o i i PI! Value during 3 Days Esrposnre to Air FIO.I-SHOWINQ How TENDENCY OF A TANLIQUOR TO FORM A PRECIPI4
TATE W R E N BROUQET TO A V A L U E DURING A PERXOD OF
pH
V A L U E OF
3
V A R I E S WITH I T S
pH
EXPOSURE TO AIR
value-during the period of exposure to air; furthermore a precipitate settled out from those whose pH values had been in the vicinity of 9. This precipitate formation is very curious. A complete series of each extract was allowed to stand exposed to air in shallow dishes for 3 days; the liqucrs were then made up to original volume and poured into 100-cc. graduate cylinders. Each was brought to a pH value of 3.0 by the addition of hydrochloric acid and allowed to stand over night. Next day the volume of precipitate from 100 cc. of original liquor was read from each cylinder. The resnlts are shown in Fig. 1. Keeping a solution of either extract exposed to air while its pH value is 9 causes it to yield an enormous precipitate when its pH value is subsequently brought to 3.0. But
The Tannin Content of Pacific Coast Conifers' By R. H.Clark and H. I. Andrews DI~PARTMENT O F CHEMISTKY,
UNIVERSITY OF
This investigation was made to determine how the tannin content of western hemlock (Tsuga heterophilla) and spruce (Sitka) bark varies with the month of the year in which the tree is cut. The samples of bark were taken from trees, either standing or just felled. I n no case had the logs been in the water. Samples for nine months of the year were analyzed for total solids, solubles, non-solubles, tannins, nontannins, and moisture. The bark came from Kingcome Inlet, B. C., from the vicinity of Kingcome River. As nearly average a sample as possible was sent from the woods.2 The samples for the months of May and June were held about 2 mo., in stoppered bottles, before the analyses were made; the effect of such seasoning might possibly have raised the tannin content slightly, as the effect of seasoning All douglas fir was found by Benson and Jones3 to be. values recorded are the average of two separate extractions. The extraction and analyses were carried out by the standard methods of the International Association of Leather Trades' Chemists, as described by Lunge and K e s ~ n e . ~ Received June 6, 1921. We wish t o thank the Powell River Co., Ltd., for their kindnessin providing the samples. a THIS JOUKXAL, 9 (1917),1096. 4 "Technical Methods of Analysis," Part I, Vol. 111. 1
2
BRITISHCOLUMBIA, VANCOUVER,
CANADA
The average sample shipped from the woods weighed about 4 Ibs. This was resampled, and about 300 g. were ground up in an ordinary meat chopper until it all passed through a 20-mesh sieve. I n most cases 25 g., in some 20 g., of the ground bark were extracted, as this amount was found t o give the required 3.5 to 4.5 g. of tanning material per liter. The extract from all the bark was quite clear and remained so for some time, with the exception of a few spruce samples, which deposited a very slight precipitate. The total solids were determined by drying 100 cc. of the extract a t 100'. The total solubles were found by evaporating 100 cc. of the extract which had been filtered through a Berkfeld filter until the filtrate was clear by the reflected and transmitted light of an electric lamp. The first 200 to 300 cc. of filtrate to pass through the filter was rejected, to avoid any correction for absorption. The tannin was d e termined by shaking the extract in a mechanical shaker with hide powder, previously tested and chromed. A clear solution of the non-tannins was left, which was evaporated, and the non-tannins weighed. The tannin absorbed by the hide powder is given by the difference between the total solublea and the non-tannins. I n the case of hemlock, the tannin content rises quite
Nor., 1921
T H E JOURNAL OF lNDUSTRIAL A N D ENGINEERING CHElMIXTRY
Month MOUTH CwT
-
CALCULATRD
cTANNIN CONTENT (BONE-DRY) Tots1 Solids Solubles Insolubles Tannins Non-tannins
January 5 . . ...... February 14.. Aprii 12 May 15.. June 15... July 20.. August 15.. September 15.., . November 1 5 . .
........ ....... ......... ....... ...
18.44 20.27 22.10 22.96 22.30 20.50 15.98 14.88 12.96
...... .... .......... .......... ........ ........ ... ...
18.11 24.7R 26.38 26.81 24.58 24.74 22.56 22.39 27 44
.... ..........
January 5.. February 14.. April 12 Mav 15 June 15.. July 20.. August 15........ September 15.. November 15..
I
Weslern Hemlock 17.78 0.66 19.64 0.63 21.66 0.45 22.28 0.68 21.70 0.60 19.16 1.34 15.48 0.50 14.57 0.31 12.89 0.07 Western Spruce 17.23 0.88 1.14 23.64 1.48 24.89 2.22 24.60 1.86 32.72 2.02 22.72 1.47 21.09 1.60 20.79 2.14 25.30
12.05 13.66 14,84 15.50 15.30 14.15 11.34 10.52 9.00
5.73 5.9s 6.82 6.78 6.40 5.01 4.14 4.05 3.89
12.01 14.96 17.19 16.58 1.5.46 15.24 15.10 16.39 17.54
5.22 8.68 7.70 8.02 7.25 7.48 5.99 4.40 7.76
regularly during the first six months of the year and then
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declines. For spruce, however, a similar regularity was not found; there appears to be a maximum in the spring of the year, then a gradual falling off with another maximum in the late fall. The accompanying curves show the tannin content in per cent, on a bone-dry basis, plotted against the time of the year in which the sample was collected. The tannin value found for hemlock is somewhat less than found for Western hemlock bark from the State of Washington by Dr. H. W. Wiley and also H. G. Tabor and referred to by Professor H. K. Bens0n.l Very few references to the tannin content of spruce could be found, the results obtained throughout were higher than expected, especially so, when compared with the results obtained by Professor Benson on a sample of sawmill bark, the history of which was unknown. The tannin content is known to be affected by many factors, among them being the length of time the log is floated in water, by how much of the cambium layer is taken with the sample, and probably by the age of the tree and length of seasoning.
SUMMARY The tannin content of freshly cut western hemlock (Tsuga heterophiZZa) bark varies from 9 to 15.5 per cent, according to the month of the year the sample is taken and averages, for the 9 mo. investigated, 13 per cent; that of spruce (Sitka) varies correspondingly from 12 to 17.5 per cent with the season, and averages about 15.6 per cent. It would appear that the extraction of tannin from the bark from the pulp and paper industries of British Columbia should be profitable.
The Alkaline Hydrolysis of Casein' By Mary A. Griggs DEPARTMENT OF
CHEMISTRY, W E L L E S L E Y COLLEQE, W E L L E S L E Y ,
It is the general belief that hydrolysis of proteins by acids gives the most satisfactory products for a study of the composition of the protein molecule or for the isolation of the different amino acids. In certain processes, however, where amino acid mixtures are required for chemical uses, such as the production of chloramines, or for the nutrition of bacteria, molds, etc., the usual methods of acid hydrolysis are not desirable because of the special apparatus required. Since alkaline hydrolysis of proteins can be carried out in iron or steel vessels and the products of the hydrolysis readily recovered, this method can often be used with advantage. Although alkaline hydrolysis promotes the racemization of optically active amino acids, this is not ordinarily a serious consideration. I n view of the scarcity of data relating to the conditions most favorable for alkaline hydrolysis, i t became necessary in connection with a larger problem to study the changes in the hydrolysis of a characteriptic protein, casein, caused by variations in time of hydrolysis and in concentration of alkali, within certain limits. Abderhalden and Brahm2 found that a residue from the hydrolysis of Shantung silk which was not hydrolyzed further either by concentrated hydrochloric acid or by 25 per cent sulfuric acid gave a considerable yield of alanine when treated with 33 per cent soda lye. Abderhalden, Medigeceanu and Pincussohn3 studied the hydrolysis of silk by hydrochloric acid (1.2 sp. gr.), 25 per rent sulfuric acid, 25 per cent sodium hydroxide, and Raturated barium hydroxide, and concluded from repeated experiments that, within narrow limits, equivalent mixtures of amino acids were obtained whether acids or alkalies were used for the hydrolysis of 1 Received
June 8, 1921. Chcm.. 61 (lQOQ), 266. I b i d . , 61 (lQOQ), 205.
12. physdol.
a
MASSACHUSETTS
the silk. Van Slyke2 used casein, among other proteins, in determining the conditions for complete hydrolysis by acid. These experiments showed that the amino nitfrogen reaches a definite maximum a t which the hydrolysis by acids is complete and that this maximum does not vary whether the temperature of the experiment is 100"or 150". The yield of amino nitrogen is also the same whether the protein is boiled for 24 hrs. with 20 per cent hydrochloric acid or heated in an autoclave at 150" for 1 . 5 hrs. with 10 per cent hydrochloric acid. The yield of amide nitrogen increased quite regularly with the time and temperature of the hydrolysis. The present work on the hydrolysis of casein by sodium hydroxide also showed the usual maximum yield of amino nitrogen, but in this case the maximum varied considerably with the concentration of the alkali and appeared much more quickly with the more concentrated solutions. The yield of amide nitrogen found was irregular owing to the volatilizing of ammonia from the alkaline solution, but in general it increased with the time of hydrolysis.
EXPERIMENTAL The material used was a sample of natural-sour casein. The hydrolysis was carried on in an autoclave immersed in an oil bath a t *150° C. The time was reckoned beginning when the temperature of the contents of the autoclave reached 150'. The casein was added to the cold water while it was being stirred vigorously, to prevent lumping, and the dissolved alkali was then added, and the whole thoroughly stirred before it was transferred to the autoclave. After hydrolysis, the autoclave was allowed to cool before it was opened. A filtered portion was then distilled into standard sulfuric acid for the determination of ammonia. 1
THISJOURNAL, 7 (1915), 915.
* J . B i d . Chcm., 12 (1912),295.
