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affinity for silicon, unless it be on the basis that both the silicon and the magnesium are prone to segregation. As cast, Melt 2823 (0.91 Si, 0.54 Mg) showed (Figure 3) rectangular or nodular blue-gray constituent and some ekeletons and needles of FeAls, a more abundant quantity of needles and irregularly shaped particles purely of X, duplex needles of F e d 3 and X, the AI-Si eutectic in moderate amount, and MgzSi in fairly large skeletons (binary eutectic?) and in small particles closely associated with silicon, as if in a ternary eutectic (Figure 9). Some of these latter complexly constituted colonies of hard particles also embraced minute fragments of X . More of the blue-gray constituent and of the &-Si eutectic was present in this than in Melt 2822, and the particles were coarser. No MgzSi or Si was observed in the quenched and aged specimen (Figure 4), which, like the annealed specimen, contained both skeletons and needles, principally the latter, of tbe iron-bearing constituents, and all of such particles were generally composed partly of FeAb and partly of X. Annealing caused the precipitation and coagulation both of Mg&i and of Si (Figure 5 ) , there being an abundance of the latter as compared with the amount in Melt 2822, annealed. This type of structural change is responsible for the loss in strength to 11,OOO pounds per square inch. The duplex character of many iron-bearing particles has already been noted. This condition was distinguishable in the unetched specimens, but was much more emphasized by etching in 2 per cent aqueous hydrofluoric acid for 10 seconds. The FeA& cores turned brown, while the X sheaths remained watery blue. The action of this reagent in aluminium-silicon-iron (as impurity) alloys containing magnesium is just the reverse of its action in alloys of t,he same base, yet without magnesium.
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Melt 2825 (4.67 Si, 0.56 Mg) presented many interesting metallographic peculiarities. As cast, there were duplex iron-bearing needles, skeletons and needles of X, skeletons and small rounded particles of MgzSi-those in the latter form grouped with silicon in the ternary eutectic-he and coarse binary ALSi eutectic, the predominating constituent, and a fairly considerablequantity of the blue-gray compound (Figures 6 and 10). After quenching and aging the MgzSi was not visible, but the silicon in excess of the solubility limit (about 1.5 per cent) was simply coagulated (Figures 7 and 11). The annealing treatment caused grain growth (Figure 8). Figure 12 gives evidence of the formation of the blue-gray constituent prior to that of the aluminiumsilicon eutectic. In Figure 13 the duplex iron-bearing needles are shown also to be antecedent to this eutectic. Figure 14 portrays a duplex skeleton with FeA13 core and enveloping X,MgzSi (right), and a silicon particle enmeshed by X . In conclusion, it should be mentioned that the slight solubility of MgzSi and the ready solubility of the blue-gray constituent lead to confusion when the specimen is etched in dilute hydrofluoric acid for 10 seconds. When there is doubt whether the black spots are polishing pits, cavities, or MgZSi partially or completely blackened by the finishpolishing with magnesia and distilled water, the specimen should be repolished down to 65 F alundum and then examined for the characteristically blue MgBi. Acknowledgment Grateful acknowledgment is herewith made to Clifford McMahon and to John L. Hester for their assistance in this experimentation.
Laboratory Preparation of Viscose’ By Earle H. Morse NUTLBY, N. J.
I
N a recent article Snellz has described the preparation of viscose from cotton cellulose. The process of making viscose from sulfite cellulose differs somewhat from that for making viscose from cotton. The writer has prepared in the laboratory viscose for experimental work which should be essentially the same as that made in the plant. Since commercial viscose is ordinarily made from sulfite cellulose, sulfite cellulose must be used in the experimental batches. The preparation of laboratory batches of viscose of a grade favorably comparable with the commercial batches differs in certain important details from the commercial production, owing to mass reactions and the limitations of the mechanical equipment for handling the larger batches. The methods here described have been in actual use by the writer for several years and have also been tested in other laboratories. From 200 to 800 grams of sulfite cellulose have been used per batch and both American and foreign pulps have been employed. With different grades of sulfite cellulose it is sometimes necessary to change details slightly to obtain identical results, but with little changes the process outlined here will produce commercially comparable products from any suitable grade of sulfite cellulose. It is not a t all difficult to make viscose, but some experience is necessary to make uniform batches. 1
Received October 31, 1925.
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THISJOURNAL, 17, 197 (1925).
If viscose is to be prepared as a routine operation it is advisable to secure the best possible apparatus. However, if only a few batches are desired it is possible to prepare viscose with the simplest of makeshift apparatus. The process and equipment described here will give good results where a considerable number of routine tests and batches are to be made. Notes as to simpler equipment which has been found satisfactory for a smaller number of batches or an occasional test are added. Treatment with Caustic Soda About 800 grams of sulfite cellulose pulp are cut into sheets about 15 cm. (6 inches) square. The cellulose as used should contain about 10 per cent of moisture, so that about 890 grams will be required to give 800 grams of dry cellulose. The sheets are piled into a wire mesh basket about 20 cm. (8 inches) deep and immersed in 8 liters of a caustic soda solution. A basket made of 4-mesh black iron wire is satisfactory. The tank into which the basket is dipped and which holds the alkali solution is preferably an open-top tank welded from light (No. 8 or 12) black sheet iron. Glass or wooden containers should be avoided. Although about an 18 per cent sodium hydroxide solution is suitable for commercial work, a concentration of 20 to 21 per cent is preferable for these small batches. Ordinary
April, 1926
INDUSTRIAL AND ENGINEERIXG CHEMISTRY
room temperatures are satisfactory. With a room temperature of 24" C. a caustic solution of 20.7 per cent has been successfully used, whereas a t 20" C. a caustic strength of 20.1 per cent gives about the same results. If the viscose is to be strictly uniform the same temperature of soaking should be used for each lot. Temperature control is less important with these small batches than with the commercial batches, however, and some variation can be allowed without serious consequences. The action of the alkali is probably completed in less time, but it is advisable to soak the cellulose for one hour so that uniformity can be maintained. Pressing
The basket with its load of cellulose is raised and the excess liquid allowed to drain back into the tank. The sheets are then removed to a press. As a makeshift a letter press may be used, though it is often difficult to get the required amount of pressure with this. A hand-operated screw jack or a small hydraulic jack are also suitable. The "baby" press made by the Watson-Stillman Company is representative of the best sort of press for routine work. The sheets are stacked on a light black iron plate with the edges of the sheets as even as possible. The pile is placed on the bed of the press, covered with another light iron plate, and pressure slowly applied, allowing plenty of time for the liquor to drain out of the sheets. The pressure is gradually increased until the weight of the pressed mass is 3.00 times the original dry weight of the pulp used. For thick viscoses the pressed weights are usually lower, down to 2.86 times the dry weight. The weight will be readily reached with less than 20 kg. pressure per square centimeter (300 pounds per square inch) of pulp surface if the process has been correctly carried out. The pressed cellulose will then contain from 13.7 to 13.9 per cent sodium hydroxide. For routine work where best uniformity is desired, it is advisable to adjust the pressed weights with the actual strength of caustic soda solution used so that the sodium hydroxide content of the alkali cellulose, as determined by titration, will be practically a constant. This constant is somewhat higher than it would be in most, commercial practice. "Crumbing"
The pressed mass of alkali cellulose must be broken up into a light fluffy mass of "crumbs." If it has been properly pressed, this can be done with any sharp-pointed instruments -a pair of needles or a pair of kitchen forks for an occasional batch. A wooden roller studded with sharp nails and working against a base plate has been used with reasonable success on quite large batches. Nothing is quite so convenient and efficient as a small double-armed mixer of the Werner & Pfleiderer type. The commercial machines have water jackets and are equipped with toothed blades and serrated bed plates. With small batches these are unnecessary, though teeth on the blades are advantageous. They can be readily cut with a small triangular He. The fluffy mass of crumbs must be kept about 24 hours, or overnight, a t a temperature of between 18" and 23" C. The viscosity of the resulting solutions will be greatly affected by the temperatures and times of this storage, and these can be varied somewhat with the particular product desired. As high as 30" C. is used in some commercial work, but below 15" C. is not satisfactory. Almost any container that is shallow and loosely covered is suitable for a small batch. In large batches, where overheating has to be avoided, sheet-metal boxes with loosefitting covers, holding about 50 pounds each, are used. The crumbs must be left as loose and fluffy as possible.
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Xantha tion
The crumbs can be mixed with carbon bisulfide in almost any type of container that will revolve. With very small batches a mason jar is convenient because one can observe the course of the reaction. If a Werner & Pfleiderer mixer is available the sulfuring can be carried out in this and a glass plate laid across the top. For routine work a 20-liter (5gallon) cylinder can be welded from sheet iron and fitted with a removable cover or head, with a heavy sight glass fastened in the head to permit inspection during the course of the reaction. An ordinary rotating wooden churn could be used for some time and is readily obtained. In the covers of the larger apparatus a 25-mm. (1-inch) hole is bored and fitted with a cork stopper. The stem of a dropping funnel is cut off to about 15 cm. (6 inches), is drawn out to a fine, though blunt, point, and fitted with a cork the size of the hole in the drum head. The amount of carbon bisulfide used is slightly over a third of the weight of alpha cellulose in the original pulp. For the 800-gram lot of pulp 288 grams of carbon bisulfide are used and fed into the mixer in four separate portions. Seventytwo grams are placed in the dropping funnel, the churn is given a few preliminary turns, and stopped with the head up. The cork is withdrawn from the drilled hole and the dropping funnel fitted tightly in its place. The carbon bisulfide flowing in through the fine opening is vaporized almost. as rapidly as it flows in. The cylinder is then rotated for about 10 minutes a t such a speed that the crumbs fall over and over each other. The three remaining portions of the carbon bisulfide are fed in a t 10-minute intervals in the same manner. The churn is then rotated until completion of the reaction is shown by the rich orange color of the finished xanthate. This may require several hours, but the time can be greatly shortened if the crumbs are very fine and the temperature is relatively high. The xanthation does not proceed satisfactorily below 20" C., and a temperature above 35" C. is decidedly detrimental. Ordinary room temperatures above 20" C. are suitable for these small batches, and there will be but little change in the temperatures of the batches during the progress of the reaction. The finished xanthate is deep orange in color and free running like sand, and should not be more moist than ordinary bread crumbs. Solution of Xanthate
The xanthate is dissolved in water to which sufficient caustic soda has been added to make about a 3 per cent solution. Sulfite pulp as ordinarily purchased for viscose work contains about 85 per cent of alpha cellulose recoverable in the viscose, making a 15 per cent loss on the original weight of the pulp. I n making up the xanthate solutions the amount of water can be calculated on the basis of 85 per cent available cellulose, although in careful work the amount of actual alpha cellulose should have been determined in the pulp. On the basis of the actual cellulose present the solution is made up to contain from 6 to 10 per cent cellulose as desired. Slightly over 6 per cent is usually used for fine Haments, 8 per cent for thick filaments or films, and 10 per cent for coating! printing, etc. Assuming a normal pulp with 10 per cent moisture and that 890 grams were weighed out at the start, there were 801 grams of dry pulp, not all alpha cellulose. With a net loss of 15 per cent of the original weight the alpha cellulose present is 756.5 grams. On the basis that an 8 per cent cellulose content is desired in the finished viscose, and that this is to be made with a 3 per cent solution of sodium hydroxide, 8699.5 grams of 3 per cent sodium hydroxide are required for dissolving the xanthate. To make this 261 grams of pure sodium hydroxide and 8438.5 grams
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of water substantially free from magnesium and calcium salts are used. This will give close to 8 per cent of cellulose in the finished viscose. Other concentrations are calculated on the same basis unless analysis later shows a need to vary them or there are definite analytical results upon which to base the alpha cellulose content. The solution can be made in any container of suitable size by hand stirring alone if necessary. In this case it is desirable and saving of much labor to cover the xanthate with the required amount of water and set aside for overnight. If placed in an ice box little ripening of the solutions will occur. The mass swells when it stands in water this way and makes the subsequent solution much easier when the stirring has to be done by hand. For small routine amounts a laboratory stirrer can be readily made by taking the fan from an electric fan, lengthening the shaft, and adding a suitable paddle blade. For routine work it is better to take a 10-gallon drum and have one head replaced by a loose cover, which can then be equipped with a suitable type of mixer giving rapid and thorough agitation. If a paddle-blade mixer is used the blades should go close to the bottom of the tank to assist in breaking up the lumps of xanthate. If the same churn that was used for sulfuring is employed to dissolve the xanthate, it is advisable to remove the xanthate completely and feed it back slowly after the required amount of water has been introduced. This aids in freeing the xanthate of any excess carbon bisulfide and in keeping the solutions of constant composition. The mixing is usually a long operation, 5 to 6 hours being used here, depending upon the type of xanthate and the efficiency of the mixer. After solution is practically complete there may be a few lumps that have not broken down and some formed from unattacked cellulose. These are kept out of the tank or storage container by filtering through a piece of iron wire screen, of about 20 mesh. The storage tank may be a convenient sized crock, a small drum, or even the mixer itself. Ripening
The ripening is carried on at room temperatures, or a constant-temperature bath or even a refrigerator may be used. At room temperatures this solution ripens at a satisfactory rate. If relatively high temperatures are used-i. e., around 30" C.-there is danger of the ripening proceeding so rapidly that coagulation will set in before the solution can be used. The amount of ripening desirable depends upon the products to be made-for thick films, it is usually not over 48 hours, for thin fibers it is carried as far as possible without thickening the solution unduly. It depends also on the type of bath and the machine used for the spinning of the fibers, etc. For thinspinning solutions about 90 hours are commonly allowed. Ordinary room temperatures are suitable here. Commercial temperatures vary between 15"and 23" C. in different plants and for different uses. Tests for ripeness are made in many ways. For film and coating work the tests are simple. A solution of magnesiumfree sodium chloride is made in varying strengths. For the formation of relatively thick films two drops of the viscose should dissolve practically clear in 10 cc. of 2.5 to 3 per cent solutions, but not in stronger solutions. For thin films or filaments the concentration of the salt solution is somewhat less, and this test is not entirely suitable for spinning solutions. The quality of solution depends largely upon the spinning bath and the machine used, and considerable experimental work is often required to adjust the viscose and the coagulant to give the best results. Filtration and Subjection to V a c u u m
At some stage the solution must be filtered and freed from air and excess carbon disulfide, etc. The solution should stand for a t least 24 hours before filtering; it can as well
Voi. 18, No. 4
stand until ready for use if allowance is made for the time consumed in filtering and subjection to vacuum. On standing, much of the air and included vapors rise to the top and form a foam, while the heavier particles settle to the bottom. Filtering is best carried out in a small plate and frame iron filter press, discharging a t the top. The filter medium is either several layers of very fine linen filter cloth or a layer of surgeon's cotton between two layers of fine bleached muslin. For small lots this arrangement can be applied to a large Buchner funnel and vacuum applied in filtering. After filtering the solution is subjected to a gentle vacuum that is gradually increased until there are no further signs of bubbles. It is necessary to free from air once more and filter more carefully just prior to use if the solutions are to be used to spin fine filaments. For this second filtering two or three layers of surgeon's cotton are used. If required to filter in more than one lot great care must be taken in pouring the lots together and in transferring from one container to another, in order that a minimum of air bubbles will be entrapped. R e d u c t i o n to Proper Viscosity
The best viscosity depends upon the use to which the viscose is to be put. For general use a viscosity such that a steel ball 3 mm. in diameter falls 100 mm. through the solution in 15 seconds will be found satisfactory. The viscosity can be changed by the addition of small amounts of clear caustic soda solution of about 15 per cent NaOH. Care must be taken in mixing as time is required to complete the addition. It will be found that a few changes in the times and temperatures as suggested will make it possible to obtain the desired viscosity as the solution is made up. Usually several runs must be made before reaching any definite conclusions about viscose and its products, and after a few trials a definite program will be adopted that will give the desired results with little variations. Precipitation
The methods of precipitation have to do with the type of product formed and also with the quality of viscose best adapted to the particular product desired. It is hoped at. some later date to present a discussion of the methods of coagulation. Acknowledgment
For checking these notes and reading the copy and for many valuable suggestions, the writer is indebted to Albert D. Conley, who has done much work in the laboratory and semicommercial production of viscose and viscose products.
Proposed Atmospheric Nitrogen Plant in New Zealand A proposal has been made to harness the latent water power in South Island, New Zealand, for the fixation of nitrogen by the arc process. A huge hydroelectric plant a t the head of Smith Sound on the southwest coast of the South Island i s contemplated. The sources of power will be waterfalls near by and Lake Manapouri. Immediately to and adjoining the flat is a large waterfall of 600 feet which, when harnessed, is expected t o generate approximately 50,000 horsepower. It is proposed to erect the 50,000 horsepower plant first and construct the Lake Manapouri one when feasible. The principal product contemplated is nitrate of lime and i t is expected that a large fertilizer market can be developed in Australasia, especially in wheat and sugar-growing sections. Raw material will be available in large quantities in the immediate vicinity of the hydroelectric plant. A large deposit of excellent marb!e is situated within half a mile of the proposed plant, and can easily be transported t o the plant by gravity inclines, narrow gage railroads, trucks, etc.
