I N D U S T R I A L A N D ENGINEERING CHEMISTRY
March, 1924
CONCLUSION
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ACKNOWLEDGMENT
As a result of the uniformly successful use of alum for pretreatment of the activated sludges produced a t Des Plaines, Calumet, and Argo, the writer believes it to be preferable to acid as a practical aid in filtration. It has the advantages of being safe to handle, there is no possibility of increasing time of filtration, it is as cheap as acid, it gives a very clear filtrate, and it is not necessary to control the amount used within narrow limits. The only disadvantage is that it may very slightly dilute the nitrogenous material of the sludge.
The operation of the plants and testing stations of The Sanitary District of Chicago is under the supervision of E. J. Kelly, chief engineer, and Langdon Pearse, sanitary engineer. Edward Bartow represented the Corn Products Refining Company and supervised tests made a t the Corn Products Testing Station. Credit is due E. H. Morgan, principal assistant chemist, and S. L. Tolman and A. H. Goodman, assistant engineers, for progress in solving the problems encountered in the filtration of activated sludges produced in the plants and testing stations.
A Sectional System of Laboratory Desks’ By P. Borgstrom TULANE UNIVERSITY
I
T is an interesting fact that chemical laboratory desks have changed but little in construction since the time of Liebig and Bunsen. The idea of sectional furniture, now uriiversally adopted in modern office equipment, has apparently found no place in the workshop of the chemist. It frequently happens that in chemical laboratories rearrangement of desks becomes desirable, particularly in small rooms or instructors’ laboratories, and with the classical style of furniture such changes are impossible without considerable expense. With this idea in mind, what may be termed a sectional type of chemical laboratory desk has been designed, which has been installed in the new laboratory of physiological chemistry a t Tulane University. Two sizes of sections, 18 and 30 inches, were chosen because they suited the conditions here-that is, a major and a minor course. The method of setting up, as well as type of section used, is shown in the drawing. At the end of the desk, A is a “finished end,” stained and finished to match the desk fronts. This end is fastened to the desk by the same method as used to hold the section together-namely, three screws a t D. B is a device to lock the drawers. C shows the section removed to receive a lead-lined trough that runs through the student, desks. E is a shelf, a small one being used in the 18-inch and a larger one in the 30-inch section. The tops are 1.25 inches thick, built up of strips, glued and doweled. On the under side of the top are cleats to hold the sections in place, as well as to prevent warping of the top. Where a sink 1
LA.
OA LOUISIANA, NEWORLEANS,
was to be installed the section was made without bottom or back and with a drawer front only. As the water, gas, pressure, and vacuum lines all run above the desk, the sink can be installed independent of the desk and the desk can be removed without the aid of a plumber. In the instructors’ laboratories a few 60-inch sections were made (combining two 30-inch sections) with a removable wall so that long apparatus which would not go into the 30-inch section could be stored. The main advantage consists in its flexibility. When time of installation came it was found that some of the rooms had been altered in size due to changes in construction, and these changes caused no inconvenience or loss in installation. Moreover, ideas of equipment of the different rooms had changed in the two years that had elapsed since the plans for the building had been drawn. If the laboratory should be moved at any time in the future, the sections could be adjusted to the new building a t relatively small expense. The one objection advanced against this system is the cost. ActualIy, 629 linear feet of desks were installed and the expense would have been 5.00 per cent less if longer sections (8 and 12 foot) had been used. This is calculated on desk frontage only, independent of the tops, hoods, and plumbing. If these factors had been included in the calculation, the cost would have been 2.73 per cent less in the longer sections. It may also be said that these desks were made a t a local cabinet works, whose specialty is office and store fixtures.
Received November 28, 1923.
SECTIONAL LABORATORY DESK
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228
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
Vol. 16, No. 3
T h e Preparation and Chemical Nature of Calcined Phosphate' By E. W. Guernsey and J. Y. Yee FIXEDNITROGEN RESEARCH LABORATORY, WASHINGTON, D. c.
HE interest of this one over the other. It is Calcined phosphate is made by heating to a comparatively high laboratory in phosprobable that the chief diftemperature a mixture of phosphate rock, an alkali salt, and carbon phate fertilizers arises ference may be a somewhat or a carbonaceous material. I f is a dry, powdery material which may chiefly from the necessity for more prompt response of be stored indefinitely without change. I t contains 25 to 30 per.cent finding a material which can plants t o acid phosphate PzO5, of which practically none is water-soluble but the greater part is be mixed directly with caldue to its water-soluble soluble in ammonium citrate solution. I f is weakly alkaline, and cium cyanamide in the eeent phosphorus. hence has the advantage over acid phosphate that it can be used in of that substance being used While the patent literamixed fertilizer with calcium cyanamide without reaction. as a fertilizer. Acid phosture on calcined phosphate This paper describes a series of experiments with a small rotary phate, the usual phosphorus is extensive, no thorough kiln made to determine the optimum conditions for the preparation carrier, cannot be mixed in study of the conditions best of the material. It is found that with a charge of phosphate rock the desired proportions with suited for the conversion of 100, sodium sulfate (as NaZS04) 15. powdered coal 15, 90 per cent calcium cyanamide, since rethe phosphorus of phosof the total P2O6 of the phosphate rock may be made citrate-soluble by actions occur which dephate rock to a citrateheating at 1300" C . for 25 to 30 minutes. W i t h a charge of phoscrease the agricultural value soluble form has apparently phate rock 100, sodium sulfate (as NaHSOJ 10, carbon 15, a conof both phosphorus and been reported. The work version of 85 per cent can be obtained under the same conditions. nitrogen, described in this paper is inThe conversion of the P2O6 to a citrate-soluble form is shown to be A considerable number of tended to give more definite due in large part to a breaking down of the physical structure of the patents dealing with calinformation on the optimum rock. A theory is offered to account for this action. conditions for conversioncined phosphate have apI t appears probable that the manufacture of calcined phosphate is which conditions determine peared during the past commercially feasible. the cost of manufacturetwenty-five or thirty years. and affords a somewhat A list of the United States patents on this subject is given at the end of this paper. They clearer insight into the mechanism of the conversion and into are for the most part quite similar in their claims, the chief the chemical nature of the material. variations being in the exact proportions of materials specified, Some of the more important results of a systematic investithe manner of manipulation of the charge, and other details of gation of the relation between conversion (the portion of total procedure. A material of this nature is said to have been put phosphorus which is citrate-soluble) ?nd certain factors, such on the market in small quantity about fifteen years ago. Its as temperature, composition of the charge, and time of heatmanufacture on a large scale, however, did not prove successful ing, will first be described. a t that time. Recent large-scale experiments have been conAPPARATUS ducted by a t least two concerns. One of these concerns reI n the later and more satisfactory experiments of the inports difficulty in getting a uniform product, while the other claims t o have obtained an entirely satisfactory material. vestigation, heating of the charge was carried out in an interWith the impetus which would be given to the development nally fired rotary kiln the internal dimensions of which were of a nonacid phosphate fertilizer in the event of the extended 9.5 cm. (3.75 inches) by 81.3 cm. (32 inches). The tilt and use of lime nitrogen as a fertilizer, it is believed that a techni- speed of rotation of the kiln could be varied to give any decally feasible process could be worked out on a commercial sired time of passage and degree of agitation of the charge. The kiln was heated in the earlier experiments by a gasoline scale. While only a small portion of the phosphorus of calcined burner and later by a simple type of gas burner. Temperaphosphate is water-soluble, a large part-at least 85 or 90 ture was measured a t the hottest part of the interior of the per cent in a properly prepared material-is available, ac- kiln by a platinum, platinum-rhodium thermocouple protected cording to the generally accepted test of solubility in 24 per by a porcelain tube. It was usually possible to maintain cent ammonium citrate, under the conditions prescribed by the temperature to within 10 or 20 degrees of the desired the Association of Official Agricultural Chemistsa2 Calcined value. There was a zone in the kiln extending from near the phosphate is very weakly alkaline. It is a dry, flourlike fire end about one-third the length of the kiln throughout powder, which may be stored indefinitely without deteriora- which a fairly uniform high temperature prevailed. MATERIALS tion of the bags, without caking, and without loss in availability of the phosphorus. From the standpoint of transportaThe phosphate rock used in these experiments contained tion it offers an advantage over acid phosphate in that it 30.58 per cent Pz06, 44.24 per cent CaO, and 9.94 per cent contains 25 to 30 per cent available phosphorus pentoxide as SiOz. The mechanical analysis of this sample was as follows: against 15 to 16 per cent in ordinary acid phosphate. FiSIZEMESW PERCENT SIZEMESH P E R CENT nally, present indications are that it probably can be made a t Over 40 0.3 120 t o 150 0.5 16.8 150 to 200 32.4 40 t o 80 a cost considerably lower than that of acid phosphate. Through 200 16.5 80 t o 120 33.5 Unfortunately, agricultural tests have not been made in sufficient number to demonstrate conclusively the parity of calI n all experiments except one the alkaline salts used were cined phosphate with acid phosphate. Preliminary tests by pure materials. One confirmatory experiment was made with the Missouri Agricultural Experiment Station and by the the commercial by-product, niter cake. Bureau of Plant Industry indicate no great superiority of Wood charcoal was used to supply carbon in the earlier experiments, but was later replaced by powdered coal without 1 Received September 26, 1923. affecting the results. * Assoc. Official Agr. Chern., Methods, 1920, p. 5.
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