1、140 INDUSTRIAL AND ENGINEERING CHEMISTRY Vol. 22, KO. 2 The heating chamber of this apparatus was essentially the same as that in Figure 14. e., a vertical inner tube to receive the sample, this tube immersed in a lead bath, and the bath heated in an electric furnace. As in determining the softening
2、 point, nitrogen was passed down through the steel coil and up through the inner tube containing the coal sample. At the bottom of the inner tube was placed a short solid cylinder of steel, somewhat smaller in diameter than the inner tube, with a flat-bottom well at its upper end. The coal to be tes
3、ted was made into a briquet and placed in the well. On the briquet rested a steel rod which passed up through guides and carried a platform for weights at its upper end. In order not to place too much weight on the electric furnace, the inner tube was supported independently of the furnace as indica
4、ted in Figure 6. Table 111-Plasticity of Coal at Temperatures below the Softening Point COAL TIME ROD NO. TEMP. ELAPSED SETTLED REMARKS a C. Min. Mm. 10 412 60 18 No further settling after 1 hour, briquet deformed 10 405 110 3 Briquet barrel-shaped at end of run 10 395 251 4 2 385 25 23 Briquet had
5、flowed up around rod, the coal 2 348 95 0 Briquet distorted quite plastic In making a run the lead bath was brought up to the de- sired temperature and the nitrogen stream started through the apparatus. The briquet was then lowered into place, the rod brought down upon it, and weights amounting to 2
6、5 pounds (11.35 kg.) placed on the platform. The rod and platform weighed 1 pound (0.45 kg.), so that the load on the briquet was 26 pounds (11.80 kg.) or nearly 340 pounds per square inch (24 kg. per sq. cm.). As soon as steady condi- tions were established at the predetermined constant tempera- tu
7、re, the position of a mark on the vertical rod was observed with a cathetometer. Plasticity in the briquet w and the difference in plasticity exhibited at temperatures be- low the softening points may be one of the factors which cause wide variation in the ease with which different coals can be briq
8、uetted. Plasticity of the sort exhibited by bituminous coals is characteristic of amorphous substances such as glass. Some investigators claim that coal and coke give x-ray diffraction patterns. This argument has been considerably weakened by a recent observation that the ash of a particular anthrac
9、ite coal gave the same pattern as the coal itself. During the course of the present investigation x-ray photographs were made of No. 10 coal and of its semi-coke, using powdered samples. No diffraction patterns were discernible in either case. Coal No. 10 is so low in ash that interference from this
10、 source disappears. Literature Cited (1) Audibert, Fuels Science Praclice, 6, 229 (1926). (2) Coffman and Layng, IND. ENG CHEM., 20, 165 (192s). (3) Foxwell, Fuels Science Practice, 3, 122, 174,206,227,276,316,371 (1924). (4) Layng and Coffman, IND. ENG. CHEM., 19,924 (1927). (5) Layng and Hathorne,
11、 Ibid., 17, 165 (1925). (6) Parr and Olin, University of Illinois Eng. Expt. Sta., Bull. 60 (1912). (7) Porter and Ralston, Bur. Mines, Tech. Paper 66 (1914). Carbon Dioxide Preservation of Meat and Fish D. H. Killeffer DRYICE CORPORATION OF AMERICA, 52 VANDERBILT AVE., NEW YORK, N. Y. T HESE studie
12、s are of a preliminary character and do not by any means exhaust the subject. Consider able temerity in drawing conclusions from such scanty observations is freely admitted, particularly since the bacterial studies do not include many of the types of bacteria common to meat and fish. Xevertheless, i
13、n view of the obvious impor- tance to the meat industry of the findings, it has been Carbon dioxide atmospheres have long been known to exercise a preservative action on certain food prod- ucts. This paper describes the results of a preliminary study of the effect of carbon dioxide on meat and fish
14、and on certain common bacteria. It is shown that meat and fish can be kept fresh longer when refrigerated in a carbon dioxide atmosphere than in air, that car- bon dioxide is absorbed by meat and fish as indicated by pH changes, and that the growth of common bac- teria studied is greatly impeded, if
15、 not actually stopped, by the presence of dissolved carbon dioxide in the culture medium. Further work on the subject is desirable on account of the increasing importance of solid carbon dioxide (Dry-Ice) as a commercial re- frigerant. thought wise to publish this preliminary discussion at this time
16、 for criticism and suggestion. In attempting to explain some of the facts of Dry-Ice refrig- eration, it early became obvious that mere refrigerating effect alone could not cover the entire situation as it was observed, especially with respect to meat and fish. Strangely enough, identical refrigerat
17、ing systems using Dry-Ice as the refrigerant 1 Received December 5, 1929. Presented before the Scientific Section of the Convention of the Institute of American Meat Packers, Chicago, Ill., October 18, 1929. I preserved meat and fish better than other perishable prod- ucts. Many statements, based fr
18、equently on very scant evidence, have been made regarding the efficiency of carbon dioxide atmos- pheres in preventing spoilage of foods. Long ago patents were issued on preservation of foodstuffs by carbon dioxide atmospheres. Many of them have proved disappointing on careful investigation , but ne
19、vertheless in the particular case of flesh foods really re- It is the purpose of obtained. markable results have been this paper to describe some investigations of this preserva- tive effect of carbon dioxide atmospheres and to point out a hitherto neglected field for further research and applica- t
20、ion to the meat industries. Effect of Carbon Dioxide Gas on Meat Questions arose early in the commercial application of solid carbon dioxide refrigeration, as to whether the gas itself had February, 1930 ISDCSTRIB L ASD E-YGINEERISG CHEXISTRY 141 any deleterious effect upon ineat stored in it. To an
21、swer this, a number of commercial samples of beef, pork, poultry, butter, eggs, and cheese were suspended in individual tin cans of sufficient size to prevent contact with the cans and to insure complete coverage of the samples by the atmosphere sur- rounding them. List of Samples Exposed Round stea
22、k 3 pounds Duck (2) Ql/4 pounds Soup meat I O3/r pounds Pork sausages 2 pounds h-eck bones 3 pounds Frankfurters 2 pounds Sweetbreads 2 pair Butter 2 pounds Beef kidneys 2 Cheese (Snappy, Kraft, Spare ribs 3 pounds Roquefort, Camembert) 2 pounds Pork trimmings 4 pounds Eggs 2 dozen Pork loins 6 poun
23、ds Lamb chops 3 pounds Bought from a retail butcher in New York City. One set of cans was connected to a sourceof a slow, continuous supply of gaseous carbon dioxide, and a duplicate set closed with air in the cans and sealed to prevent the accidental con- tamination of the air by carbon dioxide. Bo
24、th sets of cans, containing duplicate qamples and cut where possible from the same pieces of meat, were placed in a refrigerator side by side at 40“ to 45“ F. The flow of carbon dioxide through the carbon dioxide cans connected in parallel was at an average rate of 3 to 4 cubic feet per hour distrib
25、uted through twelve cans, or an average of 0.25 to 0.30 cubic foot per can per hour. The purpose of this was to insure that any deleterious effect of the gas would not be nullified by leakage of carbon dioxide out and air into the cans. The gas supply was passed through 15 feet of rubber tubing with
26、in the refrigerator before reaching the cans to bring it to the refrigerator temperature and pre- vent either cooling or warming of the carbon dioxide cans to a different temperature from the others. The samples were inspected at frequent intervals and at the end of 2 weeks a difference had develope
27、d worthy of note. These interim inspections were made only of one, or at most two cans in each set to determine approximately what might be expected of the entire sets. At the end of 2 weeks the inspector from a nearby meat company was called in to inspect all samples. He unhesitatingly discarded as
28、 spoiled the air- stored samples of pork spare ribs, soup meat, lamb chops (10 days only), kidneys, sweetbreads, frankfurters, and pork sausage. All of the COrstored samples were in good condi- tion and did not begin to show spoilage until the end of the third week. At that time the spoilage of air-
29、stored samples of meats was complete. Butter, cheese, and eggs in both air and carbon dioxide were still in excellent condition. Rough though it was, this test indicated a definite pre- servative action of carbon dioxide atmospheres. Two possible explanations offer themselves. Bacterial growth might
30、 be materially reduced by the absence of oxygen in the atmosphere around the meat or a condition might be set up on the actual surface of the meat unfayorable to f he bacteria. It seems probable that both factors are of importance. Degree of Preservative Action Later, inore careful tests were made w
31、ith the idea of de- termining more definitely how potent this preserbative action is. It was found that samples of both meat and fish, when placed in atmospherrs of substantially pure carbon dioxide, would keep twice to three times as long as when in air at the same temperatures. It was even found t
32、o be feasible to store meat and fish for several days at a temperature as high as 80“ F. in carbon dioxide. To follow the changes in the meat in B manner which would be fairly accuratcb and at the same time not too complicated for continual use with many samples, a colorimetric pH method was employe
33、d as offering a ready means of following the absorption and evolution of carbon dioxide by samples exposed to it. Chlorophenol red with a blue light filter was used as the most convenient indi- cator. By observing the condition of the samples and deter- mining their pH value changes during storage a
34、 fair idea was gained of the effect of carbon dioxide and the extent of its absorption. The charts of results of these studies show quite clearly (1) that carbon dioxide is absorbed by meat and fish; (2) that pH values proT-ide at least an approximate method of following the changes thus produced; (
35、3) that meat and fish are preserved even at relatively high temperatures by the absorption of gas; (4) that after a short period of exposure no further effect is detectable in the meat or fish; and (5) that in no case did the fall of the pH value as determined on the exposed meat even approach that
36、of beef extract completely carbonated. EXPOSUREOF SOUPMEAT TO 100%COz 68 661 ii TIME INHOURS - Change of pH Value of Beef Muscle during Exposure to COZ Atmospheres Several peculiarities are apparent from the accompanying charts, which are representative of a great many tests. Although the samples of
37、 meat were obtained from the same retail store and were presumably the same in every case, the wide variation of original pH values indicates distinct differ- ences between samples. Apparently these differences were the result of the previous history of the meat and may very well have been caused by
38、 bacterial action. In every case the meat samples used showed a slightly slower pH value than that of freshly killed beef muscle, which is in general around 6.4. Every sample of meat showed a lowered pH value after exposure to carbon dioxide at temperatures above freezing. One sample held in high co
39、ncentration carbon dioxide in a solidly frozen condition (0“ to 10“ F.) did not change. All samples removed from carbon dioxide to air showed a rising pH value. It seems reasonable to presume from these ob- servations that the absorption is almost, if not wholly, a physical phenomenon, involving no
40、more tightly bound chemical compounds than carbonic acid. The probability is that carbon dioxide is merely dissolved in the juices of the meat, from which it is easily evolved on exposure to air or slight warming, or both. Cooked meats (cold cuts) stored for as long as 10 days in carbon dioxide both
41、 before and after cooking possess no detectable off-flavor from the treatment. 142 IKDUSTRIAL AND ENGIXEERING CHEMISTRY Vol. 22, No. 2 The relatively slight drop in pH value observed in all of these tests as compared with the drop obtained by carbonation of extract of fresh beef (6.4 to 5.5) is prob
42、ably due to the rela- tively thin surface layer of the meat affected by the gas. In taking samples for pH value, thin slices were cut from exposed samples of a pound or so of meat to give a fairly representative proportion of surface to center of piece in each case. The presence of relatively large
43、proportions of the unexposed and presumably unaffected core of a piece in the pH test samples would naturally yield a high pH value on account of the buffer action of the unchanged core. The behavior of fish is similar to that of meat, although the absorption of carbon dioxide as indicated by the pH
44、 value is somewhat greater and its preservative effect somewhat more pronounced. Effect of Carbon Dioxide on Bacterial Growth In addition to the pH studies and storage tests made upon meat and fish, a series of bacteriological tests has been made to determine the effect of carbon dioxide on bacteria
45、l growth. Because of the virtual impossibility of making qualitative and quantitative cultures on either meat or fish, it was de- cided to carry on these experiments using nutrient agar plates, exposing duplicate plates to carbon dioxide and air. EXPOSURE OF COD FISH TO 100 co, I I TIME IN HOUR5 - C
46、hange of pH Value of Cod Fish Steak during Exposure to COZ Atmospheres Preliminary tests with standard nutrient agar plates made alkaline by the addition of sodium hydroxide solution showed complete penetration of carbon dioxide as indicated by methyl red, bromocresol purple, thymol blue, and phenol
47、phthalein. Sot only was the indicator color changed to the acid side by exposure to carbon dioxide, but it returned to the alkaline side by subsequent exposure to air. The procedure adopted with bacteria follows: Standard nutrient agar was seeded with the particular organism from a 24-hour growth in
48、 nutrient bouillon and two 10-cc. portions were poured into Petri dishes forming a layer about 4 mm. deep. One plate was then exposed (open) to an atmosphere of carbon dioxide in a glass vessel and the other (covered) to air. All cultures were made at room temperature (New York, summer, 1929) for th
49、e intervals indicated and at the end of the time the number of colonies on each plate was counted. Tabulation of Bacterial Counts COLONIES IN: ORGANISM TIME Air COS AIR AFTER CO? Days Staphylococcus aureus 2 1960 None . . . . . . . . Micrococcus ovalis 2 1945 350 (7 days) Micrococcus catarrhalis 2 Innumerable hTone 14 (”) Innumerable Streptococcus viridans 2 2355 175 (7%) 299 (7 days) .- .- Streptococcus non-hemo- Proteus vulgaris 5 4040 126 (3%) 164 (2 days) Bacillus coli 1 92 0 0 (7 days) Bacillus coli 5 710 3; (5%) 719 (2 days) Bacillus typhosus 1 615 . . . , . . . . Bacillus typhosus 5
