INDUSTRIAL A N D &VC ZNEERING CHEMISTRY
788
nations of the turbine with either of the two preceding types have been built and operate very satisfactorily. The principle on which they operate is that the stream of liquid is passed through the slow-speed meters until their limit is nearly reached, and when velocities are met which are beyond the limit they can conveniently handle, the stream is by-passed through the turbine. The arrangement has been found
Val. 16, No. 8
in keeping it there. The advantages of this method of measurement are that readings may be made at a distance from the tank, the mercury column may be measured fully as accurately in most cases as the rough measurement of gage glasses, and there is no liability to breakage and consequently no loss of liquid or danger to employees. Having determined the depth of liquid in a given tank, it is not difficult t.o determine its cont.ents, except in the case of horizontal cylindrical tanks with bumped heads. These present 5 very nice problem in calculation, and in order to avoid this it ir: the usual custom to resort to calibration with weighed amounts of water rather than to risk t,heinaccuracy and difficulty of calculations. However, it is not always possible to do this, in which case the methods of calculation of Ogden3 and Howell4 may be valuable. For inclined eylindrical tanks Wrigleys gives a method of calculation. SPECIFIC GRavITY RECORDS Ko less important than the measurement of volume of liquid is very often the nieasurement of its specific gravity. Various mctliods of accomplishing this have been used, btit i t is
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sacriuh, or
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quite satisfactory where wide fluctuations in stream velocity are to bc handled, and it gives more accurate readings under these conditioiis than can he expected from the flowmeters under similar circumstan(!es. The types of integrating volume recorders just discussed are particularly applicable to liquids. A somewhat similar device for measuring the volume of gases is used extensively by public service gas companie. It consists of a box divided into two equal compartments. Each of these compartments is provided with a gas-tight bellows containing gas under a comtant pressure. As gas is admitted to one compartment, the bellows in it is compressed, thus actuating a vdve system for permitting the gas to flow out again and opening the inlet to the other compartment. The movement of the valves actuates a counting device which records the amount of flow. The operation continues as long as the pressure on the outlet side of the meter is lower than that on the inlet side, altlioulyh the drop in pressure necessary to operate the meter is very small. MEASUREMENT OP S T m c VOLUME
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only recently that a meclianical device has been placed a t the disposal of the plant engineer for determining and recording specific gravity continuously. The mechanism is extremely simple yet very efficient. It consists of a float corresponding to a hydrometer arranged in a well in which the liquid is kept at constant level. The float actuates a pen for recording its motion on a dial. The d i d is operated by clockwork and shows continuously and permariently the specific gravity of the liquid passing through the line at any time. This device can be connected by a by-pass to a closed pipe line and can be made of materials that will withstand practically :my corrosive liquid. ACKXOWLEDGMEKT
The writer's thanks are hereby extended to the manufacSo far we have discussed turers of the devices described for their invaluable assistance measurement of liquid flow, in getting together the material for this article. while neglecting the very important point of measuring the volume of liquid standing in a tank. Ordinarily, the depth of Use of Glue for Paper Coating-As a result of further c o m p m liquid in a tank may be meas- tive expmimenis with different glues and with casein for paper ured by onc of three methods-a measured rod, a gage glass, coatinp. the Bureau of Standards has establishpd the fact that the amounts of glue and casein required vary almost directly or a pressure gage. The first two are understood too well to relative with the grade oi glue. The statement quoted almost universally require comment. The method of measuring the depth of that 5 parts of glue are required as compared with 4 parts of liquid in a tank by the pressure i t exerts is accomplished by casein is certainly incorrect, as it holds only for the lower grade sinking into the tank a tube connected to a supply of com- bone glues. The ratio ior u high-grade hide glue is 2 of glue to ai casein. This permits the use of much smaller amounts of pressed air sufficient to forceair out of i t against the pressure 3glue than were formerly thought necessary and leads to the of the liquid. The pressure of the air required gives a means possibility of producing a more flexible paper than can be obtained of determining the depth of the liquid. Usually the air s u p otherwise. The practical limit to which the decrease in amount of glue cau ply consists of a small hand pump and the pressure is measured pushed is set by the day-suspending property of the glue. by mercury in a U tube, although of conrse other modifications be In this respect a certain hide glue was found to be exceptional, may be used. It is necessary to use care in getting the open since it permitted working with as little as 8 per cent of glue based end of the tube to the bottom of the tank to be measured and on the --sight of the clay.
