788 INDUSTRIAL A N D &VC

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

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I,ONe,I"DIN*L sacriuh, or PISTON M E T E R , S,IOX."(i

VILVB AND P~SION AKEANCEMBNTS

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 de- vice 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

So far we have discussed measurement of liquid flow, while neglecting the very important point of measur- ing the volume of liquid standing in a tank.

Ordinarily, the depth of liquid in a tank may be meas-

ured by onc of three methods-a measured rod, a gage glass, or a pressure gage. The first two are understood too well to require comment. The method of measuring the depth of liquid in a tank by the pressure i t exerts is accomplished by sinking into the tank a tube connected to a supply of com- pressed air sufficient to forceair out of i t against the pressure of the liquid. The pressure of the air required gives a means of determining the depth of the liquid. Usually the air s u p ply consists of a small hand pump and the pressure is measured by mercury in a U tube, although of conrse other modifications may be used. It is necessary to use care in getting the open end of the tube to the bottom of the tank to be measured and

ZNEERING CHEMISTRY Val. 16, No. 8

in keeping it there. The advantages of this method of meas- urement are that readings may be made at a distance from the tank, the mercury column may be measured fully as accu- rately 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,he inaccuracy 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 eylin- drical 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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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 id 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 con- nected 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 manufac- turers of the devices described for their invaluable assistance in getting together the material for this article.

Use of Glue for Paper Coating-As a result of further compm- tive expmimenis with different glues and with casein for paper coatinp. the Bureau of Standards has establishpd the fact that the relative amounts of glue and casein required vary almost directly with the grade oi glue. The statement quoted almost universally that 5 parts of glue are required as compared with 4 parts of casein is certainly incorrect, as it holds only for the lower grade bone glues. The ratio ior u high-grade hide glue is 2 of glue to 3 ai casein. This permits the use of much smaller amounts of glue than were formerly thought necessary and leads to the possibility of producing a more flexible paper than can be obtained otherwise.

The practical limit to which the decrease in amount of glue cau be pushed is set by the day-suspending property of the glue. In this respect a certain hide glue was found to be exceptional, since it permitted working with as little as 8 per cent of glue based on the --sight of the clay.