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INDUSTRIAL A N D ENGINEERING CHEMISTRY
I n ordinary defecation practice, this low density, low purity juice is mixed with the high density, high purity, first mill juice, and it is quite evident that these suspended bodies cannot settle so well in this mixture as they could in a liquid of lower specific gravity. This thin second mill juice is therefore limed, heated, and clarified apart from the primary juice. The mixing of the rich primary mud with this thin juice seems to assist by a dragnet action in carrying down gummy and colloidal bodies and other solids held in extremely fine suspension in this thin juice. That the Petree mud as discharged by the pump of the secondary clarifier has physical characteristics entirely different from that settled out in the primary clarifier is made quite evident by the fact that the settling area of the secondary clarifier need not be more than about half that of the primary, and this in spite of the fact that it has to handle nearly double the quantity of settlings, those precipitated from the thin juice added to those coming from the primary. The mud is withdrawn from the clarifiers continuously by a diaphragm pump. Very little power is required for the operation of these clarifiers, the load varying between 1 and 2 horsepower. ADVANTAGES The advantages of this process over the old way of working are : 1-Low cost and compactness of equipment. 2-Elimination of the filter-press station, always a source of great expense and very often a breeding place for all kinds of molds and ferments and unpleasant smells resulting from their activities. That the sugar loss caused by the operation of filter presses is in excess of that shown by the figure “sucrose in presscake,” will be admitted pretty generally. The item “undetermined losses” covers a multitude of sins, and there does seem to be a’tendency for these losses to be highest when the sucrose in press cake is low-i. e., when the cake is sludged up with water and again pressed. A certain amount of deleterious impurities is unavoidably redissolved by this procedure. There are other drawbacks to the operation of filter presses. Cloths will break. A faucet here and there delivers muddy juice, with the result that some of the very fine mud, which we know impairs boiling-house work, finds its way to the evaporators. 3-A considerable saving in fuel, due in part to the actual addition to the fuel supply, since the solids, which previously formed the filter press cake, are now burned with the bagasse, and in part to the restricted and more efficiently insulated radiating surfaces. Together, these heat savings are equivalent to an increase of from 8 to 10 per cent in the amount of bagasse. 4-0ne man per shift easily replaces ten to fifteen men usually employed on the defecators and mud tanks and a t the filterpress station. 5-The money spent on filter-press cloths and plate and frame renewals can be put to other uses. 6-Greater ease in cleaning evaporators due to the practical absence of organic, solids in suspension. 7-A great improvement in the working of low-grade sugar, only from half to two-thirds the centrifugal equipment being necessary. &Better exhaustion of the molasses due to lower viscosity, and consequently less sugar losses. 9-Better keeping sugars; the practical absence of bagacillo, which cannot be washed out of the sugar in the centrifugals, means a lower moisture content and less danger of fermentation. 10-Absence of clinker in furnaces; and, as a result of all this, 11-An actual increase of 1t o 2 per cent in the sugar recovered.
There are many more points in favor of this process, such as greater comfort for the workmen, greater cleanliness, no useless dilution of juices by washing tanks, etc.l No innovation in manufacturing processes can be brought about without pretty severe scrutiny, and rightly so. Perhaps the most plausible and the most frequently voiced objection to the Petree process is the loss of the press cake as fertilizer. At most sugar mills the press cake is considered in the light of a liability rather than that of an asset; on the other hand, there are those who ascribe almost supernatural pokers of raising cane to this evil-smelling refuse. 4
Louisiana Planter, 73, 307 (1924).
Vol. 16, No. 11
On the basis of a table of analyses shown in Noel1 Deerr’s book, the fertilizer value of the press cake is so low (less than 93 per ton) that the cost of distribution a t most places is far in excess of its value. But even this value is more than offset by the effect the Petree mud has on the bagasse ash. This ash contains in most cases so much clinker that the amount of available potash in it is practically negligible. The lime content of the mud returned to the bagasse raises the fusion point of the ash sufficiently to leave it in a friabIe condition with the bulk of the potash in available form. Thus the bagasse ash, which has in most cases been a liability, becomes an asset and the press cake is replaced by a material of higher fertilizing value, which can be quite easily distributed. Another criticism deals with the fact that the percentage of sucrose in cane under the Petree process is based on the weight of the clarified juice instead of the weight of the raw mixed juice. There was really no reason to assume that there would be any difference between the two methods. The proof that the sucrose in cane figure is not affected by this modification is furnished by the factor sucrose per cent cane to sucrose percent first mill juice, which was found to he the same in every instance where data for comparisons were available whether on weight and analysis of cold or hot juice.
Determination of Phosphoric Acid in Fertilizersiz By 3. E. Breckenridge AMERICAN AGRICULTURAL CHEXICAL Co., CARTBRBT, N . J.
C O O P E R A T I V E work on determination of phosphoric acid in phosphate rock shows very good checks with the volumetric method as compared with the gravimetric method. In phosphate rock, however, there are no sulfates, which seem to be a disturbing factor in the volumetric method when applied to mixed fertilizers and- acid phosphate. Many laboratories recognizing this standardize their alkali against a known solution of acid phosphate and do not use the standard given in the A. 0.A. C. Methods. As a result of work done in the writer’s Iaboratories it has been found that precipitating the sulfates with 5 per cent barium nitrate solution, the method as given can be used, and gives results agreeing closely with the gravimetric method.
METHOD Boil a 2-gram sample for 30 minutes in a 200-cc. flask with 30 cc. of nitric acid plus a few cubic centimeters of hydrochloric acid. Add 50 cc. water and boil. Add while hot 5 per cent barium nitrate solution (50 cc. for acid phosphate and 25 cc. for mixed goods). Allow to cool and proceed with volumetric method.
RESULTS Gravimetric 19 31 Maximum Minimum 9 Ii7 16 52 Average Number of determinations, 9.
--VOLUMETRIC-Regular Ba(N0s)z 19 47 19.37 9 78 9.5s 16 90 16 52
Although the addition of ammonium nitrate is supposed to overcome the disturbing feature of the sulfates, in general work erratic results are obtained when the volumetric method as given in Association of Official Agricultural Chemists, Methods, 1920, p. 3, is used on acid phosphates and mixed fertilizers. 1 Presented before the Diwsion of Fertilizer Chemistry at the 68th Meeting of the American Chemlcal Society, Ithaca, N . Y., September 8 t o 13, 1924. A. H. McDowell, 1 Work done by M. H. Plngree, Baltimore, Md.; Charleston, S. C.
