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concentration from boiling ; otherwise these two operations have the same end in view : namely, the separation of the water from the juice by evaporation. The difference between them in the order of the proceedings is-1. That concentration precedes boiling. 2. That the one operates on larger bodies than the other. 3. That the process of clarification intervenes, the object of which is to separate the substances precipitated by concentration, in order to produce a clear, limpid juice for boiling. 4. That the concentration takes the juice at the density of defecation to carry it to 20 or 250 hot, while boiling takes it at this density to carry it to 40 or 41° (areometrical), a point nearly sufficient for a good crystallization.
The process of defecation generally causes a loss in the weight of the raw juice of l° or 11°, for instance a juice that weighed 7 areometrical degrees at 10° (55°) of the thermometer would not weigh, after defecation, more than about 6°. If it weighed 10° the defecation would reduce it to 84 , in fact the loss of weight in this case is nearly in proportion to the density of the juice.
Concentration operates by the intervention of fire, which reduces the water to the state of vapour; and as the tension of vapour is regulated by the temperature, it follows that, to produce the quickest possible evaporation, under the atmospheric pressure, it will be necessary to expose it to the highest temperature that it can take under this pressure, which is that of ebullition.
There are other methods of producing concentration. Achard, for instance, by steam, (not high pressure), acting on the boiler which contained the juice to be evaporated. This he effected without ebullition, but very slowly. In England syrups are often evaporated by means of steam ; but there it is so highly compressed that the liquor enters into ebullition as if it were exposed to a naked fire. All these means of evaporation are more or less complicated, and on that account rather deviate from the common routine of agricultural operations. The author therefore confines himself to the most simple mode of evaporation for concentrating the juice of the beet root. The great problem is,
“ To exhibit the simplest apparatus for concentrating the juice in the shortest possible space of time, and with the least alteration in the quality.”*
* In the process of boiling, great improvements have recently been made in France, steam being now generally employed for that purpose in the several sugar establishments.
§ 1. Of Evaporating Apparatus, or Boilers for Concentration.
Boilers of copper are thought to be the most suitable for this purpose. It has been proved both by theory and practice that the vaporization of liquids is best effected in wide open vessels. It is then important that the evaporating surfaces should be as large as possible, and exposed to the direct action of the fire. But herein a difficulty presents itself, which is this :
The beet root juice will suffer by concentrationareduction nearly equal to four-fifths or five-sixths of its volume, according to its richness, and this reduction ought to take place in a very short time, which, of course, is only to be effected by a fierce fire. The great difficulty in this case is to prevent the sugar from burning. But the better way perhaps will be to give a brief analysis of the several modes actually in use.
1. Achard's Plan of Concentration.
This chemist recommended from experience the concentration by steam, for which purpose he had two boilers placed for one defecating boiler. These were charged only about six inches deep, consequently the process is very slow, and, in the author's opinion, by no means advantageous to follow.
2. Plan adopted at Chatillon-sur-Seine.
Here the concentration is effected in boilers equal in capacity to those of defecation, thus each defecating boiler has its evaporating boiler. The process of concentration requires ten or twelve hours to bring the juice to 22 areometrical degrees boiling. This is a very imperfect system.
3. M. Chaptal's Plan of Concentration.
This chemist employs one evaporating boiler for one of defecation, and this boiler, 15 inches deep, receives all the juice of one operation. The surface of this boiler is calculated to contain about 8610 English square inches, (555} square decimetres) capable of evaporating per hour as many killogrammes of water (555} killo. =1221lbs). M. Chaptal concentrates the syrup to 28°boiling, which corresponds with 32° cold. To obtain this result it was necessary to reduce the body nearly to a sixth, which would require three or four hours, a period
considered to be too long. M. Dubrunfaut therefore does not advise a single boiler for this operation.
4. Plan of Concentration Generally in Use.
This method consists in the adoption of two evaporating boilers, for one of defecation. All three have bottoms of the same dimensions ; and as the two former are capable of receiving all the juice furnished by one defecation, they are made rather more than half the height of the latter. Thus admitting that the one contained 2000 litres, (70 cubic feet), each of the others would contain rather more than 1000 litres, (35 cubic feet). This plan is practised at many of the manufactories. Still some are of opinion that it is not the most advantageous to adopt.
5. M. Crespel's Plan of Concentration.
Each boiler of concentration is 2m32 (about 91 inches) long, and 1m06 (39 inches) wide, and presents a surface of 3600 square inches. There are six of these for one of defecation. An evaporation takes place during the defecation of about an 18th part of the mass. About 280 to 300 litres (62 to 67 gallons) are poured into each concentrating boiler, which is nearly four inches deep. The juice is kept boiling till it has reached 31° of Beaumé. This operation will require five hours. The 1800 litres (400 gallons or so) contained in the six concentrating boilers will be reduced to 220 or 240 litres (50 or 54 gallons) of syrup, according to the richness of the beet roots in saccharine matter.
The above is M. Crespel's own account, but since it was written he has made many improvements, and particularly in his evaporating apparatus, which is composed of two rows (batteries of six boilers each, forming a set for each of the two defecating boilers with which they are intended to act.
Each of these boilers may be about four feet in diameter by one foot in height. The following is the mode of using them : The charge of one of the defecating boilers being drawn off clear, is distributed by equal portions over the six boilers which compose one of the batteries. They are then submitted to a brisk evaporation till the juice has acquired a density of 20°, or nearly so. The contents of the six boilers are then united in one, to be clarified, which process will be described hereafter. The concentration thus advanced but to 20° (areometrical), does not expose the juice to the risk accruing from too thin a body.*
* This reduction arises not so much from evaporation as from the scum and froth removed during the defecating process.
This M. Dubrunfaut thinks the best plan he had hitherto seen adopted, although in his opinion it still admitted of improvements. He therefore proposes the following as his own :
6. Plan of Concentration.
It has received the sanction of experience, and will be particularly advantageous in large concerns : three boilers are supposed to be necessary, each affording a charge of 500 litres (114 gallons) every half hour, making 24,000 litres, or 5472 gallons in the 24 hours.
The author has ascertained that the syrup, to undergo a suitable evaporation, ought never to present in the boilers a layer reduced to more than 5 centimetres (2 inches) in depth. This is the minimum of reduction to which it can be brought without danger; for beyond that the ebullition will not operate well.
It is well known that to produce the greatest evaporating effect, the juice ought to be spread over the largest possible surface, but that this must necessarily be limited by the reduction in bulk which the juice will undergo in concentration. The inconvenience arising therefrom is overcome in the following manner. First, the juice is so distributed over the surface as not to complete its evaporation there; but when the layer shall be reduced to 5 centimetres (2 inches), this same juice is removed to a vessel presenting a smaller surface, and where, consequently, it undergoes a new evaporation ; then, when on this new surface it shall again be reduced to 5 centimetres (2 inches), it is removed to another still smaller, and so on. However, three of these removals have been found to be sufficient, in the progress of which the juice has been exposed to the action of the fire but an hour and a half.
It will be well to ascertain the quantity of water evaporated from a given quantity, say 500 litres (114 gallons) of juice, the mean richness of which is 6 areometrical degrees, and which by concentration is raised in density to 30 degrees when cold. A calculation is then given, by which it appears that these 114 gallons will be reduced to 18} gallons (82 litres), 9 gallons of which are water. There must then have been evaporated during the concentration 95 gallons = 919 lbs. of water.
respel, I am informed, has materially altered his plan since this was written,
In adopting vessels of three different calibres to effect the concentration of 500 litres (114 gallons) of juice, and the consequent evaporation of 95į gallons of water in half an hour, it has been taken for granted that the boilers were worked simultaneously and continually. It would, of course, be necessary in such case, that they should be discharged and recharged every half hour. But in order to do this properly, their evaporating surfaces should be exactly proportioned to the quantities of liquid received by each of them, and to the effect which they are intended to produce. Thus the first (500 litres) ought to have an evaporating surface equal to 861 square feet. The juice will be distributed over a bed of 10 centimetres (4 inches) in depth, and as it ought not to continue in a state of ebullition more than half an hour, after this time it will have lost half its bulk of water, and will thus be reduced to 5 centimetres (2 inches) in depth. The juice will then be transferred into a second boiler, the surface of which will be equal to 430 square feet. From thence it will be removed to a bed 4 inches deep, as in the first instance, and after evaporating half an hour this will also be reduced to 5 centimetres, losing in the above time 275 lbs. of water. There then remain 28 gallons of syrup, which will be taken to a third boiler, presenting a surface of 215 square feet. This last vessel will be capable of evaporating 14 gallons in half an hour, making a total of 437 litres (100 gallons) of water evaporated, whereas only 95 gallons were wanted. If the size of these vessels be objected to, it is very easy to provide against this evil; for instance, instead of one boiler of 860 superficial feet, one might employ four of 215 feet, and in place of No. 2, which is said to contain 430 square feet, two of 215, and so on.
§ 2. Of the Appendages to the Evaporating Vessels. The walls of the furnaces ought to be strongly built, and protected on their upper edges by sheet copper.
A skimmer is wanted for each boiler, proportioned to their respective sizes, and also some good areometers to indicate in a constant and uniform manner the point of concentration. Each evaporating boiler should have a wooden or earthen vessel to receive the skimmings, which are removed during the process of concentration.
$ 3. Process of Concentration. The apparatus for this purpose, it has already been stated,