I N D U S T R I A L AiYD ENGINEERING CHEMISTRY
April, 1930
absorb all the sugar liberated as concentration increases. The mother liquor does not get viscous and does not cling to the crystals. They are easily washed white and ultramarine blue is not required. Fully 85 per cent of the available sugar is now recovered as white directly out of the evaporator thick juice; the remainder furnishes high-grade seconds which ran be washed to produce a second-grade white of excellent quality. Then there is no remelt a t all. American Method-The
Work at Glendale
In the American heet-sugar houses all the available sugar is recoyered in two boilings as compared with four in Europe. The American method requires much less factory equipment, labor, and supplies, and is cheaper to operate. The method is easily adapted to cane work. The white cane granulated is in all respects identical to the standard beet granulated in America, and is much superior to the best Java white produced. One hundred pounds of this white cane granulated can be delivered for the cost of producing raw sugar plus 8 cents. About twenty years ago the owners of the beet-sugar factory a t Glendale, A h . , decided to grow sugar cane instead of beets. They imported seed cane from Sinaloa, Mexico, and set it out on their estates. Later they brought mill equipment from Louisiana and secured a growing Louisiana cane crop, to be milled together with their Mexican cane. Many different cane varieties came to their Arizona mill. The cane juice was purified by the Javan acid-thin juice method, according to Harloff and Schmidt, but for the recovery of the sugar all resemblance to Javan methods ceased. The evaporator thick juice was boiled to white sugar in the same manner as had been done with the beet juice, and the results were the same. Fully 80 per cent of the sugar contained in the thick juice was recovered in first jet as a standard white granulated. This sugar kept in the warehouse without difficulty even in that hot climate. The green sirup was boiled to grain; it delivered seconds of a good quality and molasses which was well exhausted. %gar cane did not do well in southern Arizona, however.
367
The enterprise was considered a failure and the factory was dismantled. At t h a t time the writer did not realize that he had accomplished something which was ahead of the best Javan white-sugar practice. He simply believed that he had equaled the Javan results, never dreaming that the work of the Javan sugar department is much inferior to the American practice of making white beet sugar. He did not know then about the handicap caused by the use of exhaust steam for boiling white sugar and the troubles experienced in Java on this account. Later investigations revealed to him that the costly and intricate juice-purifying methods of Java become entirely superfluous and obsolete as soon as the pan floor is operated according to American beet-sugar rules. Equal results are easily obtained if the evaporator sirup of any well-equipped raw-sugar houses is relimed and sulfured to a certain degree. It is then easily atered through Vallez thick juice filters and a very clear and brilliant pan supply liquid is obtained. Such standard white cane granulated is very much superior to the Java white; it keeps better upon storing, and it costs much less to produce. Means of Furnishing Live Steam
I n fitting up a raw-sugar house for such white-sugar work, several provisions can be made for furnishing the live steam for sugar boiling and for decreasing the amount of engine exhaust produced. About 90 pounds of live steam are required to boil 100 pounds of white sugar. In saving this amount on the steam consumption of the power plant, the engine exhaust is decreased by a like quantity. Diesel motors could be installed to supplant part of the steam power. For a motor-driven mill house all the power could be generated by Diesels, thus avoiding the production of any exhaust steam. In this case pressure evaporators fed by live steam should be used for concentrating the juices. An important portion of the bagasse is then left unused. It becomes available to firms who make paper pulp out of bagasse and affords a source of income, independent of the sugar market, to the owners of the central.
Magnesium-Manganese Alloys' G . W. Pearson 1215 SOUTH TRESTON ST.,TULSA,OKLA.
H E R E are few references to magnesiuni-manganese alloys in the literature and the conclusion3 reached by the investigators are varied. Schmidt (5)says that the manganese appears as an intermetallic compound; Bakken and Wood (1) report that the alloys are solid solutions up to a t least 3.20 per cent; G a m ( 2 ) says that, whilc some manganese is present as solid solution, most of it is in the elenientary state as small blue-gray particles scattered through the crystals of magnesium.
T
Preparation of Alloys
Attempts made by the writer to produce alloys of higher manganese content were unsuccessful. The alloy highest in manganese had 2.7 per cent and showed solid-solution structure with rather wide grain boundaries and a somewhat dirty appearance under the microscope. This alloy was obtained by holding magnesium a t about 750" C. in contact with five times its weight of manganese lumps for 5 hours. 1
Received December 2 , 1929
It was possible to pour only about half of the magnesium out of the manganese, either because of its entanglement in the sintered manganese or because of the formation of a solid magnesium-manganese alloy. After the molten magnesium had been poured out, the tempwature was raised sufficiently high to melt the entire contents of the crucible. The magnesium all boiled out, leaving manganese with no appreciable quantity of the lighter metal. A stick of magnesium was plunged into the liquid manganese, but it volatilized and ignited with explosive violence, forcing some manganese out of the crucible. In order to see what diffusion of manganese into magnesium was taking place, rather large pieces of manganese were pushed into the molten magnesium. Since these pieces splintered up below the surface, the two metals came into contact without an intervening coat of oxide. The melt n a s then held a t about 750" C. for 2 , 3, and 4 hours and permitted t o cool in the furnace. Later, specimens for microscopic examination were cut from the lower portionof themelt.
L Me at L'op, Two l o i l o s of Alloy. Mn at Bofrom. x l2a
Fielire
Figure 7-Mn
~
Fieure 2 MP af I'op Narrow Second Lone, Wide Third, M n .'t Boftem. x 125
Inclusion In Ma. Crack in Lower Portion of Mn. x 20
Microscopical Examination
In thwe specimens t.he same zones do not show up in all cases, although there seem to be two quite definite zone^ of intermediate material. Figure 1 shows four differrnt. areas; the whitest is the magnesium (probably solid solut,ion), tlie black i p the magnesium-rich area, the fine-grained zoiie of material is rdativel? rich in manganese, and coarser strncturn below it is the pure manganese. Figures 2 and 3 sliow tlic sane gradations but very little of thr black zone. Thc blaak spots in the magnesium a t tbe top of the picture are lioles caused by pieces of manganese which were torn out am1 shoved into the soft mabmesium. The black spots in the manganese are also holes, the metal being so hard and brittle
Fieurc 1 Me a t Top and mght, M n a* Bottom and KIPhr x 125
Pieure 8 &owor Rirlht Ehd of Crack Seen in Figure 7.
x
540
that it is ilifficitlt to get a good snrfuce. Figure 4 show3 a boundary between the magnesiinn and the magnesium-rich dark zone. Figure 5 s h o w the gradation front mairganese to the manganese-rich material. Figure 6 sliows the transition from the magnesium-sich alloy to the inangnnese--ricii alloy. Oxidation by air and wnter polishing have somcthing to do with t,he dark color of thc Inagnesium-rich material. Fignre 7 is a photograph at low powx of B manganese inclusion with the alloy zone hrdweeti thc niapicsiuni and the Inanganesc. The significant thing in the picture is the crack t11a.t developed in the manganese and which was filled with magnesium-rich mateiial. Althougli it does not show up in this particular picture, tlie magiiesiiim iii this fissure is of
Fiaure 9
Alloy i n Which Upper End of Crack T~rminales. X 540
Fiaurs 11-MB
at Top, M n at Boftem, Alloy In Between X 360
iliffereiit nature from the alloy zone surroiiridiug the manganese. At the moutli of the crack there is a rather wide band of alloy, which is thc only material besides the magiiesium that shows up in Figure 8. In t h 2 picture the nature i l f the niagiiesiiirn a t the mouth of the crack seems to be different from that farther along the cmclt, where more of the (lark manganese-rich material had come out of solution as the alloy cooled. Figure 9 shows the nature of the alloy in nhicb the crack terminated. The fact tbat tile crack did not go clear through the alloying layer might irieaii that this was in a semi-solid condition at the time thc crack developed. Tlie bright areas in this picture are manganese and the ground mass in which tbcy appear is magnesium-rich material. One of t,he leads in this ground inass is continuous with the crack in FiEillures 7 and 8. The magnesium backgrouiid then grades off ta a material which looks like pure niapesium and which showed 1.57 pcr cent of manganese on analysis. Too niuch iriiportaiice should not Lc attached to simple
FiI?urc le
Bsundary. Alloy at Tup and Pure M n at Bottom Of Piccure. X 548
FiDure 12-Pure M n Crystallizing Ouf of Allay Zone.
x
5*0
analysis. Unless special precautions were t,aken to secure a uniform melt, check analyses were riot obtained. Because of the differrncp in demity of the two metals, there WBP considerablr tendency to segregat.s. Some of the black alloy which surrounds the manaarieae iixlusion in Figure 7 W R ~ removed and tested for manganese. It showed 37 per cent manganese, but t h i i is not entirely reliable because the brittle manganese chipped off and the soft magnesium came out very easily when the dent,ist’s biirr, with whirh the work was done, touched either of the bounding metals. Figure IO shows a typical boiindary between the manganese and t.lie manganese-rich allny. The holes in the manganese should not be eonfused with the magnesium ground mass in the upper port,inn cbf the picture. fimire 11 ?how magnesium at, the t,np, rnanpmeae at the bottom, and the intennediat.e mnes of alloy. Figure 12 iS that. of an a,lIoy zone in R melt that stayed in the furnace 5 longer time and got somewhat hotter than did the series 7 to 11. The distinctly white masses arc manganese. This
INDUSTRIAL A N D ENGINEERING CHEIIfISTRY
370
structure was typical in certain zones. It occurred away from large masses of manganese and was more likely to be found near places where there were islands of the alloy. The difference in the appearance of the manganese masses in this and in Figures 9 and 10 is due, perhaps, to a different rate of cooling. The microstructure that is most difficult to account for is the ground mass in the alloy or, more definitely, the material which is black in Figures 1 and 4. It appears as a narrow line in Figures 2 and 11 and again may be the material which immediately surrounds the manganese in Figure 12. If the manganese as such is present in this structure, it must be in very small particles. There is some evidence from work with oil-immersion objectives that there are globular masses of a second material with the magnesium. These globular masses may be an intermetallic compound which, upon slow cooling, breaks up into pure manganese and magnesium. There was a further structure that was not accounted for and was attributed to iron until malysis showed iron less than 0.1 per cent. It was a pearlitic arrangement with one
VOl. 22, No. 4
set of bands appearing yellowish brown with a 2 per cent nitric acid etch. One of the lamina is magnesium and the other may be a manganese or an iron compound, the iron being an impurity from the crucible. This structure shows up very clearly in material that has less than 0.1 per cent iron. It can be seen in photographs 37 and 38 of Gann’s paper (9). Summary of Results
Study of the microstructures of magnesium-manganese alloys shows that the solid solution area extends beyond 2.7 per cent manganese. I n the higher ranges that metal may show up as angular masses. In the still higher ranges, 35 per cent and up to pure manganese, it appears as irregular masses in a background of magnesium. Literature Cited (1) Bakken and Wood, Am. SOC.Steel Treating Handbook, p. 560 (1929). ( 2 ) Gann, MIntng M e t . , 9, 449 (1928). (3) Schmidt, Z . Meletallkunde, 19, 452 (1927).
Temperature Changes in the Formation of Soluti onsl*z K. M. Watson and 0. L. Kowalke DEPARTMENT OF CHEMICAL ENGISEERISG, UNIVERSITY
OR a study of the unit
F
OF
WISCOSSIN, MADISON, WIS.
A method has been demonstrated whereby the dif-
in an infinite amount of solu-
ferential heats of dissolution of a salt at various contion of concentration C. This operations of leaching is ordinarily termed the “difand e x t r a c t i o n i t is centrations and temperatures may be calculated from ferential heat of soIution.,, n e c e s s a r y to establish relathe thermochemical data generally available. tionships from which the temSo-called “dissolution charts” have been devised c, = specific heat capacity of solution perature changes taking place from which the temperature attained i n the adiabatic c,‘ = specific heat capacity in such processes may be preformation of solutions may be readily predicted. of solid solute dicted. If the process is conA study has been made of the equilibrium temperat = temperature of solutures attained by the solid particles of a typical salt tion ducted under approximately t’ = temperature of solid adiabatic conditions, the temwhen dissolving in water. solute p e r a t u r e of t h e s o l u t i o n formed will be a function of its concentration and must be The relationship between temperature and concentration evaluated as such, I n addition, if dissolution is treated solely changes in such a dissolution process is expressed rigidly in as a diffusional process, the temperature of the surface of the Equation 1. However, its integration and application redissolving solid must be known in order to establish an ac- quire knowledge of the relative rates of temperature changes and of the relative masses of the solid and of the liquid. The curate concentration difference as a driving force. In the present investigation working generalizations are introduction of such relationships would seriously complicate presented regarding these two types of temperature varia- the equation. A form, much simplified, which is of sufficient accuracy for many Durposes,, may- be iustified by a considerations. -... tion of ihe probable reiative magnitucles of t h e terms on the Changes i n Solution Temperature during Adiabatic right-hand side of the equation. It will later be shown that Dissolution in all ordinary cases dt’ will be somewhat smaller than dt. The dissolution of any material is accompanied by a ther- The term m’/nz mill in practical cases be limited to the mass of mal effect, generally an absorption of heat in the case of solute as a maximum which may be dissolved in a unit mass neutral inorganic salts. The transfer of solute from a dis- of solvent to form a saturated solution. In most ordinary solving solid surface to a solution must therefore be ac- cases this ratio will not exceed 0.1. The value of c,’ for companied by a transfer of heat. Consider a definite mass, most solutes will be less than 0.3, while for aqueous solutions m’, of solid solute in contact with a definite mass, m , of solu- c p will approximate unity. I n many cases it may then be tion of concentration c. If the system is adiabatic, the heat assumed that (m’/m)c,’.dt’ is negligible compared with c,.dt. absorbed in dissolution will be derived from the sensible heat This assumption should result in a satisfactory engineering approximation except in cases where very concentrated soluof the solute and solution. Thus, tions are prepared which involve a high value of m’/m. On - AH.dm’ = - AHm.dc = c,m.dt $. cp’m’.dt’ this basis, or
+
- AH.dc = c,.dt (m~/m)c,~.dt‘ (1) AH = heat absorbed in dissolution of a unit mass of solute
1 Received January 12, 1930. 2 Submitted by K. M. Watson in partial fulfilment of the thesis requirement for the degree of doctor of philosophy, University of Wisconsin.
dt = -(AH/c,)dc
(2)
This expression establishes a simple and useful relationship between the changes in the temperature and in the concentration of the solution in an adiabatic process of dissolution.
