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The paper industry uses controllers for various purposes. The instrument is used to regulate the operation of the grinder. The controller is also employed on the paper-making machine itself t o regulate the flow of steam to the drier rolls so that paper with just the correct amount of moisture is obtained. This is an important matter to the paper maker, for too high moisture may mean that the paper will spoil in storage while too little wil! make the paper brittle.
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Among the many high-temperature operations in which controlling pyrometers are employed may be mentioned galvanizing, carburizing of steel, gas-fired and oil-fired heattreating furnaces, the blast furnace in the steel plant, core ovens in the foundry, annealing furnaces, etc. I n conclusion, it may be said that wherever heat is used and where temperature, either low or high, is important, there is a possible use of the automatic temperature controller.
Some Scientific Aspects of Packaging and QuickFreezing Perishable Flesh Products* I-More Rapid Freezing Means Better Preservation Clarence Rirdseye GENERALFOODSCOMPANY, GLOUCESTER, MASS
T IS the purpose of this article to contrast the characteristics of air-frozen and quick-frozen products. For present purposes air-frozenJ slow-frozen, and sharp-frozen will be considered as synonyms referring to products frozen in modern "sharp freezers" with a minimum temperature of about 10' or 15" F. below zero (-23.33' or -26.67' C.). "Quick-frozen" will be used to designate products that have been frozen by direct immersion in a liquid refrigerant such as sodium chloride brine, or by indirect contact with a very cold liquid refrigerant such as calcium chloride brine. Animal flesh is made up largely of countless elastic-walled cells filled with a semi-liquid protein gel. This gel contains a large percentage of water in which are dissolved appreciable quantities of sodium, calcium, potassium, magnesium, manganese, iron, and zinc salts in the form of chlorides, phosphates, sulfates, bromides, and iodides. Water in which these salts are dissolved does not freeze homogeneously. Instead, fresh water ice begins to freeze out of the cellular and intercellular material when the temperature of the product is lowered to about 31" F. (-0.56' C.), and, as the temperature is lowered still further, more and more fresh water ice is formed, leaving an ever more concentrated solution of the various salts. The water content of fish is not entirely frozen until the temperature of the flesh has been reduced to approximately -70" F. (-56.67" C.).
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Percentage of Freezing at Various Temperatures
Complete figures are not available to show exactly what percentage of the moisture content of fish is frozen a t various 1 Received
February 8, 1929.
AVERAGE
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temperatures, but from the fragmentary evidence at hand it may fairly be inferred that a very large part has been solidified by the time the temperature has been lowered to 25" F. (-3.89' C.). From Figure 1, which shows the time required to thaw a fillet in the center of a filled 50-pound insulated shipping container, it will be noted that the temperature rise is very rapid from -10" F. (-23.33' C.) to 25" F. (-3.89" C.) the curve thereafter remaining comparatively flat until the temperature has reached about 31 " F., after which it again shoots up very rapidly. Figure 2 shows that the time-temperature curve in sharp-freezing a carton of fillets is very much the same shape as that in Figure 1. Taylor* says that a t 5' E'. (-15" C.) about 15 per cent of the water remains unfrozen; while a t 31" F. (35" C.) below zero, about 2.5 per cent remains liquid. Plank3 has ascertained that a t 29.3" F. (-1.5' C.) only 42 per cent of the water is frozen; while the very last of the water, which is more closely bound to the muscle colloids than the rest, is not frozen until a temperature of a t least 68.8" F. (57" C . ) below zero is reached. These facts have been used in the preparation of Figure 3. Crystal Formation
During the period in which the bulk of the moisture content is being frozen, the individual ice crystals are continuously increasing in size, by accretion. After the temperature has reached 25" F. (-3.89' C.), by which time most of the water has probably been frozen, the growth of individual 2 Taylor, "Refrigeration of Fish," Appendix VI11 to Report of U. S. Commissioner of Fisheries for 1926, p. 601, Washington, 1927. 8 Plank, Z. gcs. Kiiile-Ind., 81, 141 (1925).
R o w TEMPERATURE 65-A
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Figure 1-Temperature Rise during Thawing Period in Center Package of a 50-Pound Insulated Corrugated Shipping Container of Haddock Fillets
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Figure 2-Time Required to Sharp-Freeze and Quick-Freeze In Center of a 2-Inch (5-Cm.) Carton of Haddock Fillets
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May, 1929
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crystals apparently largely ceases. Therefore, we may for conveniencerefer to thetemperaturezonefrom31-F. (-0.56' C.) down to about 25" F. (-3.89- C.) as the "zone of maximum crystal formation." And since, when substancer crystallize, the size of the crystals depends upon the time allowed for them to form, it is obvious that the more quickly flesh is passed through this zone of maximum crystal formation the smaller the crystals in the frozen product will be.
contact with a very cold liquid refrigerant, heat is extracted from them with such extreme rapidity t.hat, instead of being chilled almost uniformly throughout their bulk, the freezing zone advances toward the center as a sharply defined line, on one side of which the flesh may be frozen hard while on the other crystallization has not commenced. By referring again to Figure 2 i t will be noted that the package of fish which required 10 hours to harden in a sharp-freezer needed only 1'/* hours t o quick-freeze. The chart also shows that, although the whole package required 6.66 times as long to sharpfreeze as it did to quick-freeze, 1 cc. of tissue a t the center of the quick-frozen package passed through the zone of maximum crystal formation in 25 minutes, or fourteen times ae fast as in the sharpfrozen package. Thus quick-frozen flesh is passed through the zone of maximum crystal formation so very rapidly that the resulting ice crystals are too small to be capable of materially rupturing or compressing the tissues. The contrast between s h a r p and quick-frozen flesh is clearly illustrated in Figure 4. A is a photograph of a piece of sharpfrozen haddock fillet cut "across the grain." This fillet was taken from near the center of a 3Qpound tin of parchment-wrapped fillets of a well-known brand frozen in 36 hours in a large Boston plant. Even a c a n a l glance at this illustration shows the serious damage done by the crystals. Much of the tissue was reduced to an amorphous mass which escaped at the cut surface when the product thawed. The remaining flesh has been compressed into tough bundles utterly incapable of re-absorbing the mois ture from the melted crystals. Such a sharpfrozen piece of flesh spoils rapidly; and even when cooked immediately after .a.r"l-r A T W*TCS c o " ~ ' ~ , ~ ' " F ~ * e ,e",, , ______ being thawed, is dry, pulpy, lacking in nutrient value, and _____._-__...._.._._~.~..~... totally without the delicious flavor of the fresh product. Plavrs 3-Perccntage-Ternperarvre Curve of Cryatdllzarlon In Figure 443 shows a section of quick-frozen flesh from the Fre'rsszlnp Flesh Products center of a 10-pound packageof haddockfillets. It is perfectly In usual sharpfreezer practice fish is frozen in from 12 to 48 obvious that no large crystals were formed when this fish was hours, the heat being removed from the surface principally by frozen, and that no damage has been done to the flesh. Such convection air currents. The heat transfer is so slow that a fillet, even though it may have been held in storage for moisture at the center of the fish begins to crystallize almost several months, is still truly fresh fish. as soon as that near the surface, the whole mass of the fish gradually becoming first firm and then hard. From Figure 2 it will he seen that if a 2-inch ($em.) package of fresh fish requires 10 hours to freeze hard in a sharp freezer, a small group (about 1 cc.) of cells in the center of the p a c b g e will require approximately 6 hours to p a s through the zone of maximum crystal formation. It is thus evident that in sharpfrozen fish a great deal of time is allowed for the formation of large ice crystals, which are sometimes as much as an inch (2.5 cm.) in length. "",C"
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Effect on Tissues The formation of these large sharp-pointed ice crystals within and between the cells results in a more or less serious rupture of the more delicate of the tissues and a compression of the tougher and more resktant fibers into dehydrated layers or bundles.' Moreover, this badly ruptured sharpfrozen flesh autolyses more rapidly,&and is more susceptible to bacterial decomposition than fresh undamaged flesh. During the comparatively slow process of sharp-freozing, a considerable amount of moisture is lost by evaporation from the surface.' Exact figures on the amount of this loss are not available; but i t probably averages from 1.5 to 4 per cent on fish frozen in blocks, 3 to 7 per cent on singly frozen fish, and 2 to 6 per cent on hulk-frozen meats. When flesh products are quick-frozen by direct or indirect Cook, Love. Viekery, end Young, Avilrdinn J. Er~il.Bid. N e d . Sei., 9, 15 (1928). 8 Taylor, O h &., D . 523. Pefenoo, Rcfiigrroling World, September, 1924.
Figure 4-(Al
Sharp-Frozen Haddock FlUefi (61 Quick-Frozen Haddock Fillet
Figures 5 to 10 illustrate microphotographically the damage which large ice crystals cause to individual cells of s h a r p frozen haddock fiilets and beef tenderloins. These photcgraphs were taken under the supervision of R. P. Bigelow, of Massachusetts Institute of Technology. The cells of the fresh, unfrozen product are entirely normal in appearance; the quick-frozen cells show not the slightest damage from ice crystals; but the sharpfrozen cells are obviously badly r u p tured. It is interesting to note that the sharpfrozen and quick-frozen haddock cells came from the fillets illustrated in Figures 4-A and 4 B , respectively. Professor Bigelow made a further careful study of muscle tissue from fresh, sharpfrozen, and qiiick-frozen haddock fillets, and the following extract from his report is illuminating:
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INDUSTRIAL AND ENGINEERING CHEMISTRY
Fisuip 5-Cells of fresh unfrozen beddock. Note that the cells are perfect and have a full rounded appearililce.
Figure 6-Cells from quick-frozen haddock. Note cello perfect in every way.
Vol. 21, No. 5
Pieurc ?-Cells from a haddock fillet frozen in the regular manner. Note TUPturer caused by ice erystsis and Bat empty eppcriience of ~ 1 1 %
Haddock
Figure 9-Cells from beef frozen in 30 minutes in qmick-lreeziny apparatus. Note that cells are unbroken.
Eigure 10-Cells from beef frozen by oidinary commercial cold-atorage methafs.
Beef Tenderloin
On examination. the fresh haddock appears t o be well preserved. The structure of the muscle fibers is well seen, the fibrillae being quite distinct and in places the striations arc visible. Between the fibers is the connective tissue. Blood vessels and capillaries can be seen, containing nucleated blood corpuscles. and in several places very beautiful pictures are seen of nerve fibers showing clearly the axis cylinder and the sheath. The quick-frozen haddock showed apparently some disintegration of the connective tissue between the fibers, probably due to a slight maceration during the handling between the death of the fish and the commencement of freezing. But in s m e places the nuclei of the connective tissuc can bc seen and the blood vessels show distinctly the nuclei in their smooth muscle fibers. The striated muscle fibers of the muscle amear to be in good condition, showing distinctly both the fidlillae s In this material, as well as in the fresh and the c m ~ striations. haddock. the nuclei within the muscle fibers are not very distinct The slow-lrozen haddock has a very different appearance in cross section under the microscope. as well as when;een in the hand. The muscle fibers seem to be swollen. Together with the differences in size. these muscle fibers show verv different structure. In the first place, they are firmly presshd together so that only a very narrow space appears between them, and they are not evenly distributed throughout the specimens as in the case of the fresh and the quick-frozen fish. Between these masses of pressed fibers were large empty spaces, or large spaces filled with an amorphous material which may be the result of the disintegration of connective tissue. The connective tissue seem to have entirely disappeared as such from the specimen. This makes i t v&ry diffiNlt to prepare a block for section cutting, because as soon as one attempts to cut a small Piece of the flesh it falls anart. I think these slides show a very big diserencc between the slow-frozen haddock on the one hand and the quick-frozen and the fresh material on the other.
Shrinkage
For obvious reasons, loss of weight by evaporation during quick-freezing by any of the better known methods is very much less than in sharp-freezing. When the products are properly protected by highly vapor-proof packages before being frozen, the shrinkage is negligible. At one large quickfreezing plant the average shrinkage in freezing haddock fillets wrapped in Moistureproof Cellophane and packed in 10pound cartons is less than 0.25 per cent. Table I shows that there was practically no shrinkage in various packaged dressed meat products experimentally quick-frozen a t the above plant. Tabfe I-Loss of Weishf durlne. Quick-Freezing of Certain Packaged Meata PRODVCT BEPORG Farzarrrt; APTBBF R S R I X N ~ LbS. os. Lbs. Os. Sirloin s:eak-r chow .enderloin
11
6
5
4111
lP/. 10"'
Other Advantages of Quick-Freezing
When certain forms of meats and poultry are sharp-frozen, the extensive drying of the surface, sometimes apparently associated with a partial oxidation of the fats in and immediately under the skin, causes an effect known as "freezer-burn," which considerably lowers the value of the products. Freezer-burn was entirely absent in the packaged meats con-
INDUSTRlAL A N D ENQINEERING CHEMISTRY
May, 1929
sidered in Table I, and did not occur even with such bulk products as green pork bellies frozen in direct contact with the metal belts of the quick-freezing apparatus. Perhaps equally important, from the marketing point of view, was the
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fact that the color and odor of the packaged meats was not changed at all by the quick-freezing. “Drip”-leakage of moisture from the product during the thawing process-was very slight indeed.
Recent Developments in the Manufacture of Sulfuric Acid’ S. F. Spangler CnElricnL CONS-IYUCTION
A
NY review of recent developments in the manufacture
of sulfuric acid that aims t o point out tlie present trend and predict future developments must necessarily recognize the changes in the use of this most important chemical in the last few decades. Sulfuric acid has been recognized since the beginning of chemical industry as being one of the most important chemicals and a necessary material in the manufacture of very many other chemicals. Chamber Piants At the beginning of this century about half of the sulfuric acid produced was used in the maiiufacture of phosphate fertilizers and the remainder in the manufacture of explosives, oil-refining, the pickling of steel pla.te, and the preparation of heavy chemicals. For most of these purposes the lead chamber plant producing an acid of 60’ 136. (77 per cent I4SOJ strength was the most suitable and most common type of plant, since only 52’ B6. strength of acid is required in the fertilizer trade. The stronger “oil of vitriol” or 66” BE. (93 per cent H*SO,) acid was made, when required, by concentration of 60’ BP. acid by direct lieat in retorts or cascade concentrators. If an especially pure, strong acid was desired, such Concentration was effected in glass or platinum vessels. The comparatively small requirements for fuming sulfuric acid-i. e., acid of over 100 per cent H,SOI strengthwere taken care of by a few scattered contact plants employing platinum-mass as the catalytic agent, with none too sa&
co., CIIIIRLOrnTB, N.c sulfuric acid. The “mixed acid” used in the manufacture of explosive nitro compounds required sulfuric acid both as one of its direct constituents and indirectly in the manufacture of nitric acid, tlie other constituent. For the manufacture of nitric, a sulfuric acid of 66’ RP. strength was required, while fuming acid was the most suitable form of the sulfuric acid used as a direct constituent of the mixed acid. The result of the war demand was to compel operation of all existing chamber plants in excess of their normal capacity, the rapid building of various types of concentrating plants to produce 66’ Be. acid from chamber plant acid, and a large increase in the number of contact acid plants. This period saw the successful application of acid-proof masonry in this country to the construction of the Glover and Gay-Lussac towers of chamber plants and of tower types of concentrating plants on a large scale and the shdt from pyrites to brimstone as the principal source of sulfur dioxide gas. This latter shift was accompanied by the replacement of brick furnaces by more efficient types, such as the rotary Glens Falls burner and the Vesuvius burner. Such plants as continued to use pyrites as a source of sulfur dioxide generally replaced their brick ovens with mechanical furnaces of the Herreshoff or Wedge type. The contact acid plants continued to use platinum as the catalytic agent and the sudden scarcity of platinum caused by the war demands will not soon be forgotten by the cheniical industry. With tlie close of the war the demand for 6G0 B6. and fum-
Contact Acid Plant Showing Very Compact Arrangemen8 Con?pared w i t h Chamber Plant of Equal Capacifyin Background
factory an efficiency. The usual source of the sulfur dioiide gas used in both chamber and contact plnnts n a s iron and copper sulfides (pyrites), wlich commonly were roasted in brick ovens. To a small extent brimstone was used as a source of the sulfur dioxide gas by direct combustion in similar oveus. The rapid development of the explosives industry during the war period caused an enormous increase in the demand for *Received Much 11. 1929.
ing sulfuric acids declined rapidly, though the subsequent growth of the dye industry eventually brought a resumption of tbe demand for mixed acid The fertilizer industry contimed to demand chamber plant acid, but the depression in the fertilizer trade forced many of the weaker plants out of business and prevented expenditure of funds for all but the more urgent repairs. A new factor came into the industry in the increase in the demand for sulfuric acid from the rapidly expanding oil industry. This called not only for additional
