I N D U S T R I A L A N D ENGINEERING CHEMISTRY
778
It is impossible to apply t h e figures given to coal in storage. The samples all passed a 200-mesh sieve, and are far more readily attacked by oxygen than a pile of lump coal would be. I n fact, coal sized a t minus 100 and plus 200-mesh suffers smaller loss than minus 200-mesh size, as shown in the comparative figures given in Table IV. TABLEIV-COMPARISONOF THE HEAT Loss IN MINUS 200-MESH AND MINUS100 AND PLUSZOO-MESHCOAL,OXIDIZED AT 125' C. FOR 5 HOURS 100f200-Mesh Loss -200-Mesh Loss Per cent Per cent Pittsburgh 0.49 0.38 Upper Freeport 0.58 0.56 Pocahontas No. 6 0.28 0.27 New River 0.35 0.35
Vol. 16, No. 8
A coal of minus 100 and plus 200-mesh loses, on the average, 7.8 per cent less in heat than a minus 200-mesh coal, whose surface area is about twice as great. Since a minus 200-mesh coal has nearly five hundred times as much surface area as an equal weight of 0.5-inch lumps, it is evident that the figures shown in the tables are an enormous magnification of the loss in the average coal pile.
ACKNOWLEDGMENT
-
The writers wish to acknowledge their indebtedness for the helpful suggestions of A. C. Fieldner, superintendent and supervising chemist of the Pittsburgh Station.
T h e Melting Point of Acetyl Salicylic Acid' By Mark E. Putnam THE Dow CHEMICAL Co., MIDLAND, MICH.
N AN article by Dahm2 there is a careful description of a melting point apparatus especially designed for this work. I n some particulars, however, this author has not emphasized several very essential points necessary for securing a melting point covering a very short range. The range given by Dahm is 133" to 135" C., which is unusually large. The method given herein will serve to shorten this range and a t the same time give great uniformity in the checking of all samples of the pure product. I n connection with the Dahm apparatus, it has been found advisable to hold the melting point tube containing the sample as far as possible above the surface of the heated sulfuric acid bath, for its initial position, or a t least somewhere near the top of the neck of the flask. The bottom of this same melting point tube should extend an inch or more beneath this supporting rod, just as indicated in the Dahm apparatus. Needless to say, the walls of the melting point tube should be very thin (such tubes are best made by drawing out thin test tubes) and the samples of acetyl salicylic acid employed should be very finely powdered and carefully dried a t 85" to 90" C. for 15 to 20 minutes. With such precautions carefully observed, the determinations are made in the following manner :
I
*
The temperature of the sulfuric acid bath is raised to 120' C. and observations are immediately begun on the rate of further heating. The most satisfactory rate found in this laboratory has been taken as 3 " C. per minute, and after some few experiments this rate can readily be attained and carried from 120 O to 140 O C. without much variation. When the rate of heating is found to accord with 3 O C. per minute, and the temperature of the bath is exactly 130" C., the melting point tube is introduced and the observation taken. After the product has melted, the rate of heating of 3' C. per minute is again checked. All determinations are rejected where the rate of 3 " C. per minute is found to be greater or less by 5 seconds in a 60-second interval, within the range 120" to 140" C.
It will be found that the sample of acetyl salicylic acid in melting passes through three well-defined stages: (a) moist stage, ( b ) formation of first globule, (c) complete liquefaction with definite meniscus. Naturally, the appearance of the second stage is that usually considered as more closely representing the true melting point. The following observations were made on three samples of acetyl salicylic acid put out by three separate manufacturers. The thermometers used were glass spindles 31.8 cm. (12.5 inches) in length, reading from 100" to 140" C. and graduated 1 2
Received April 11, 1924. THISJOURNAL, 11, 29 (1919).
in tenths of a degree. They were calibrated by the writer for every one-half degree Centigrade between 124" and 137" C., as against a Reichsanstalt thermometer reading from 95 " to 150°, graduated in two-tenths of a degree, and without any appreciable correction in the range here concerned. Sapple 1 C. 133.5 133.8 133.4 Average 133.6
Sample 2 O
Sayple 3
c.
C. 133.4 133.5 133.3 133.4
133.5 133.4 133.8 133.6
From these averages, therefore, the melting point of pure acetyl salicylic acid may be given as 133.5" C. I n order to give a more severe test to this method of determination of the melting point, two separate observers were given these same samples of acetyl salicylic acid and asked to construct a melting point apparatus after Dahm's description and proceed with the determinations as described above. Their results are as follows: Sample
c.
6 3 6 2
Observer A
B B A B
A
Here the range may be given as approximately 133.3" to 133.6" C. I n other words, the melting point of the purest acetyl salicylic acid that could be obtained does not vary more than between these limits (133.3' to 133.6' C.), and accordingly this is recommended as the correct range for the melting point when taken under conditions described; the value 133.5 " C. is therefore representative of the mean for this range. It is interesting to note the many variations in the melting point of this product as recorded in the literature. The British Pharmacopeia gives the melting point of 133" to 135" C., the Japanese Pharmacopeia that of 135" C., the German, 135" C., and the New and Nonofficial Remedies, U. S. A., 128" to 133" C. The determination given by Dahm, 133" to 135" C., covers too wide a range, but when interpreted as meaning 133' C., referring to incipient fusion, and 135" C., for complete transparency, the figures are sufficiently clear. Cappelli3 has described the conditions emphasized in this paper and has given as a final value 132" C. for incipient fusion, which corresponds to the moist stage described herein. ' These observations were made in the spring of 1920 in collaboration with W. A. Van Winkle, for whose careful work the writer expresses his gratitude and appreciation. 8
Giorn. chim. i n d . applicata, 2, 291 (1920).
August, 1924
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
779
Low-Temperature Distillation of Farmville, N. C., Coal‘ By W. E. Giles and F. C. Vilbrandt UNIVERSITY OF NORTH CAROLINA, CHAPEL HILL, N. C.
T
HE coal from the
This low-temperature distillation study of the Farrnville coals of nature of the volatile Products distilled from different Farmville mines of North Carolina indicates that this excessively smoky and high volasamples of coal at low ternt h e Deep River tile coal can be converted into commercial gas and a low volatile Peratures in the early stages Valley field of east-central residue suitable for domestic consumption. The presence in the coal of heating varies according North Carolina is rated a of complex paraffin hydrocarbons easily liberated at low temperatures to the smoke-producing good gas coal with respect to is girren as the cause for the smolpproducing tendencies andfor the t e n d e n c i e s of the coal. its volatile matter, accordcharacteristic atmospheric disintegration of this coal in storage. Ac c o r ding1y , the coals ing to the classification of from the Farmville mines, coals by Bone,2 who rates coals having a volatile matter content between 32 and 38 being excessively smoky, should liberate large quantities of per cent a t 900” C., with a n oxygen to hydrogen ratio of heavy hydrocarbons very rapidly when subjected to low1:2. The Farmville coal falls in this class if only volatile temperature distillation. The gases liberated should be rich matter is considered, but its oxygen to hydrogen ratio is 1:1. in the heavy hydrocarbons, and at very low temperatures No studies are recorded that show any data on laboratory or would be unsuited for gas for ordinary domestic heating plant tests on the applicability of this coal for such purposes as purposes, because of their high sooting tendencies. gas coals. RAWMATERIAL The outstanding characteristic of this coal is that of giving off excessive amounts of smoke and frequent “flare backs.” The coal used in this investigation came from the Farmville On this account it is in disfavor as a household fuel. It is said mines of the Deep River coal field, comprising parts of that the use of this particular coal on the fleet blockade run- Chatham, Moore, and Lee Counties, North Carolina. This ners of the Confederacy enabled the Union forces to spot and coal field has been estimated to contain 100,000,000 tons capture them readily because of the large amount of smoke available a t depths not exceeding 1600 feet. The sample used pouring from the stacks. The engineers on locomotives using in this investigation was a face sample taken from different this coal claim that the flues become quite clogged with the parts of the mine. The coal is brilliant black, retaining its soot and also with some fine coal dust accompanying the soot. luster on pulverizing; the fracture is conchoidal. Sulfur apThe fines thus produced are the result of disintegration of the pears mainly as “ball” sulfur. When mined the coal is hard coal on being heated, for the coal shows this property of dis- and lumpy, but on exposure to the air it disintegrates after a integrating from lump into fines on exposure to the air. short time t o “fines,” leaving but a small portion as lumps. The efficiency of boilers depends largely upon the quantity APPARATUS and nature of those constituents of the coal that can be gasified a t a low temperature, but which do not condense I n order to maintain the different temperatures accurately upon the boiler surfaces, or which are not reduced below the and for long periods of time, an electric furnace was built with temperature for their complete combustion. An evaluation electrical control. The furnace was of sufficient size to hold of the products of low-temperature distillation of these coals a retort of 1 kg. capacity. assists in understanding why this Farmville coal is notoriously The retort (Fig. 1) was made of 3.2-mm. (‘/V-inch) steel, smoky. electrowelded 162 X 102 X 264 mm. (6 X 4 X 10 inches) inside Inasmuch as the coal as mined cannot be used efficiently dimensions, calculated to hold 1kg. of the coal. On using the either in the boiler room or in the homes, some heat treatment coal that was screened to pass 13-mm. (‘/2-inch) mesh and be is necessary to convert the 100,000,000 tons that are in sight retained on the 3.2-mm. (l/&xh) mesh, there remained an ininto illuminating gas and the residue into coke, which is sufficient air space above the charge, so the charge was made to finding much favor in the households a t the present time. equal 907 grams (2 pounds). The top of the retort was I n addition to the above, further studies were outlined to made of 13-mm. (l/%-inch)steel provided with holes to bolt the investigate the smoke-producing tendencies of this coal, top to the container and also with three holes, one for charging, which is notorious in this characteristic. The coal was one for the pyrometer well, and the third for the stillhead, subjected to a series of low-temperature distillations in a for carrying off the gases and the volatile matter. The conlarge retort a t temperatures maintained constant by electrical denser system consisted of a tar trap with a tapping petcock control. The products obtained a t these low temperatures, a t the bottom, and three glass condensers sealed into a unit which ranged from 200” to 660” C., were carefully analyzed. with glass-blown joints. Receivers were supplied a t the From studies on some British coals by Burgess and Wheeler,3 bottom of each condenser. The gases were collected over in which the smoke-producing tendencies of the several water containing sulfuric acid. The entire set-up consisted of types by low-temperature heat treatment were investigated, the electric furnace, A , the steel retort, stillhead, tar trap, it was concluded that this property was due entirely to the three glass condensers, four glass receivers, and a gasometer presence or formation of the higher hydrocarbons of the assembled as shown in Fig. 2. paraffin series, while the extent of the smokiness was due DISTILLATION to the rapidity with which these hydrocarbons were disengaged by the heat applied. Porter and Ovitz4 claim that the A 907-gram mmple of the freshly mined, graded coal was 1 Received December 4, 1923. charged into the retort and the retort sealed with steam 2 “Coal and Its Scientific Uses,” 1918, p. 68. Longmans, Green & ‘20. gasket and sodium silicate to prevent leakages. This sys8 J . Chem. SOL. (London), 97, 1917 (1910); 99, 649 (1911); 106, 131, tem was then tested for leaks. The furnace was previously (1914). heated to approximately the desired temperature before the 4 J . Gas Lighting, 107, 343 (1908).
