Fat-Extraction Apparatus for Feeds CHAS. E. WEAKLEY, JR., West Virginia Agricultural Experiment Station, Morgantown, W. Va.
end to keep the water level constant. The copper bath is covered with 6-mm. (0.25-inch) hard asbestos board supported on a 2 5 mm. (1-inch) wood frame, leaving a 25-mm. (1-inch) air space between the bath and the asbestos board cover, except on the top. Figure 2 shows one end of the setup in detail. The bath is heated by a 500-watt tubular, immersion water heater, and the temperature is controlled by a 25-cm. (10-inch) plate-type rheostat, having twenty-eight regulatory steps from 150 to 500 watts. The length of the asbestos-covered bath is 150 cm. (59 inches) with a front-to-rear depth of 26.5 cm. (10.5 inches), this depth being required for the rubber tubes which connect the condensers. Five ether condensers are cooled with one stream of water, making it necessary to have four water outlets, with needle valves, across the rear of the top shelf. The two waste overflows empty into drains at each end in such a way that the amount of water being discharged can be seen and the needle valves can be adjusted properly. A constricted lipped container (length 85 mm., outside diameter 28 mm.) holds the ether and collects the fat. A funnel-top filter tube, 100 mm. long, rests on the top of the constricted fat container and is held upright by the funnel top. This filter tube holds the sample of feed and is made up as follows: A cupped perforated tin disk is pIaced in the bottom beneath a 10-mm. asbestos (acid- and alkali-washed and ignited) pad on which
T
HE ordinary Soxhlet extraction apparatus is not only fragile but requires a large amount of space, especially where large batteries are necessary as in feed control work. Figure 1 shows a compact, rugged, and easily operated unit which has been in successful use in this laboratory. It is very economical of solvent, requiring 0.2 kg. (0.5 pound) of ether for twenty determinations if no recovery is made.
FIGURE 1. FAT-EXTRACTION APPARATUS This unit consists of twenty large test tubes with an inside diameter of 35.5 * 0.5 mm., and a length of 280 mm. each. Metallic zinc dust, wrapped securely in tin foil, is placed in the bottom of each tube to make the heat transfer more efficient and to eliminate the possibility of breakage when the fat container is placed in position. The condensers consist of test tubes with an outside diameter of 31.25 * 0.25 mm. and a length of 115 mm. each. A short collar of 32-mm. heavy-wallrubber tubing supports the smaller test tube on the top of the larger one and a strip of tightly wound flannel about 25 mm. wide, just below the rubber ring, centers the condenser tube and aids in the complete condensation of the ether. Several layers of flannel strip are wrapped to such a thickness that the inner tube fits snugly into the outer one. The outer tubes are heated in a copper water bath having twenty cups for the tubes and a copper tube condenser on each
FIQURE 3. ACCESSORIES the feed is placed and then covered with a thin layer of asbestos (this asbestos layer together with a small amount of the bottom pad is removed with the feed for the crude fiber determination). A metal cup, made from a short piece of 13-mm. (0.5-inch) block tin pipe by soldering in a perforated bottom, rests on the asbestos layer. This holds the contents of the feed tube together, distributes the ether drip, and keeps the feed from raising up and channeling. TABLE
I. COLLABORATIVE RESULTS
West Virginia, results
% 1.62 6.17 2.73 3.20 6.11 3.10 4.12 6.56 3.12 3.46 Av. 3.91
Ether Extract Avera e results of 63 la%oratories
% 1.49 6.29 2.72 3.26 5.26 3.19 4.16 6.46 3.17 3.48 3.95
The results obtained by the use of this apparatus have been found to check those obtained by the use of the Soxhlet apparatus. Table I gives the results from 53 feed laboratories on check samples sent out by the Department of Agriculture in comparison with those obtained with this apparatus. The results show close agreement. Figure 3 shows the accessories necessary for the operation
FIGURE 2. DETAILOF APPARATUS (All dimensions in millimeters)
388
SEPTEMBER 15, 1936
ANALYTICAL EDITION
of the apparatus: a pair of straight-end tongs to remove and replace the metal cup, feed funnel, and fat flask; a straight funnel tube to add ether; an ether bottle with constricted tip for a tin container with twenty places for the feed funnels, of such size as to fit a high-form 20.4-cm. (8-
389
inch) desiccator; and a tin container with twenty places for the fat flasks, of such size as to fit a 20.4-cm. (8-inch) desiccator. RECEIVED May 21, 1936. Published with the approval of the Director, West Virginia Agricultural Experiment Station, as Scientific Paper 167
Lignin in Douglas Fir The Pentosan Content of the Middle Lamella A. J. BAILEY,' College of Forestry, University of Washington, Seattle, Wash.
I
N AN EARLIER communication (1) a method of isolating
the middle lamella of wood was described. The isolated material was subsequently analyzed for lignin by a micromethod (2) developed for the purpose. The present report describes the analysis of another sample of middle lamella, which was isolated by the same method, in order to establish further the composition of the lamella by the identification of a t least a portion of the unknown 29 per cent. As was pointed out earlier (I), several investigators produced evidence indicative of the presence of hemicelluloses in the middle lamella.
Methods of Hemicellulose Analysis An inquiry into the prior work on hemicelluloses brought to light such an overwhelming mass of incomplete, contradictory, and apparently inaccurate information that there is little wonder that the nomenclature is so unsatisfactory. A brief but reasonably complete bibliography (3, 9-11, 17, 20-23, 27, 34) on hemicelluloses, including recent excellent reviews, offers a summary of present knowledge; hence i t is unnecessary to epitomize the experimental work or to take up in detail the viewpoints of the various investigators. Inasmuch as the estimation of the hemicelluloses-rather than their constitution-was the primary consideration, only the analytical methods need discussion here. Unfortunately, there is no method of making a complete analysis of hemicelluloses in a single sample. It is even impossible to define hemicelluloses in a way that has analytical significance. Supposedly, they are anhydrides of hexose and pentose sugars which are soluble in dilute alkalies and which are less resistant to hydrolysis by dilute acids than the remainder of the plant tissue. It is well known that these properties do not furnish a means of sharp distinction. There is no known method of determining the total hemicelluloses or the total hexoses in a single sample. Pentoses are usually determined by conversion to furfural, which may be estimated by oxidation or precipitation methods. Hexoses are usually determined by oxidation of the sugar or by conversion to the phenyl hydrazone or osazone (S, 18,19, 30, 3s-36). While 2 pure carbohydrates can be characterized fairly easily, their identification or quantitative separation from mixtures is exceedingly difficult. An attempt to determine the total hemicelluloses was made by extracting a sample of wood with hot water, and then subjecting the residual wood to hydrolysis. The hot-water extractive of oven-dry Douglas fir (Pseudotsuga tazijoZiolia) powder which had been put through a 100-mesh screen was 13.68 per cent; the subsequent loss in this sample, based on the original oven-dry weight of the wood, due to hydrolysis by 2 per cent sulfuric acid was 15.99 per cent; the loss in unextracted wood when refluxed with 2 per cent sulfuric acid was 27.15 per cent. On the basis of Schorger's definition, 1
Present address,lInstitute of Paper Chemistry, Appleton, Wis.
that hemicelluloses are insoluble in hot water but are hydrolyzed by heating with dilute acids at atmospheric pressure (.%), i t would seem that the total hemicelluloses in Douglas fir constitute 16 per cent of the wood. That this is not accurate is shown by the fact that the extractive plus the loss by hydrolysis is greater than the loss by hydrolysis of the unextracted wood. In other words, the hot water alone either extracts some hemicelluloses or changes some constituents so that they are soluble in the dilute acid. Further evidence that hemicelluloses are removed by hot water alone was found by an examination of the hot-water extractive. Treatment with phenylhydrazine and acetic acid in the cold yielded no mannose phenylhydrazone. When the hot water extract, however, was made up to a concentration of 5 per cent with hydrochloric acid, hydrolyzed, neutralized, and treated with phenylhydrazine and acetic acid in the cold, a small quantity of mannose phenylhydrazone was formed, together with a large quantity of an as yet unidentified compound with a melting point of 235" C. Hence, it may be concluded that mannan in Douglas fir is soluble in hot water but is not hydrolyzed by it, The total mannan by Schorger's method (18, 29) was found to be 5.33 per cent (Schorger found 6.65 per cent). After filtering off the mannose phenylhydrazone and other material from the hydrolyzate, heating in the presence of an excess of phenylhydrazine yielded the brownish yellow oily drops of the osazone of arabinose, phenylglucosazone, and another crystalline solid. When the hot-water extract, with no prior treatment, was made up to a concentration of 12 per cent with hydrochloric acid and distilled, the addition of thiobarbituric acid solution to the distillate produced furfuralmalonylthiourea. This fact extends earlier knowledge of the resistance of pentosans to hydrolysis to include not only those that occur in purified cellulose or those that are readily hydrolyzed by dilute acids, but also to those which are removed by hot water. In other words, hot-water extraction alone removes a t least three hemicelluloses and other carbohydrates. Likewise, there seems to be no way of determining the hexose hemicelluloses in a group in a single sample. Pentose hemicelluloses, however, can be distinguished easily from hexoses. Since the existing knowledge of hemicellulose chemistry was insufficient to permit an even reasonably complete determination, it was necessary to attempt to ascertain the hemicellulose most likely to occur in the middle lamella. Prior work pointed the way: Ritter and Fleck (16) found that the pentosan content of springwood was greater than that of summerwood. It was suspected that the higher volumetric fraction of lamella in the springwood was responsible. Other speculations (16), many of a teleological nature, however, had been voiced, showing the mechanism of chemical metamorphosis from pentoses to lignin, hence the possibility of a close relation between pentosans and the middle lamella.
