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T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y A SUGGESTED FORM OF VISCOSIMETER B y W. C. COPE Received July 21. 1917
T h e usual form of viscosimeter is based on t h e proposition of passing a given quantity of oil or other liquid contained in a cylindrical vessel a t a specified t e m perature through a n orifice of definite dimensions in a variable length of time. The viscosity of t h e liquid under examination, then, is obtained b y comparing t h e time taken for passing a like volume of liquid, such as rape seed oil, through t h e orifice under similar conditions. A criticism of instruments of this kind is: (I) t h e height of column of liquid is variable and t h e first half of t h e liquid collected comes through in less time t h a n t h e second half due t o less head of liquid in t h e viscosimeter; ( 2 ) a n oil of t h e nature and consistency of engine oil a t ordinary laboratory temperature will flow only a few cubic centimeters per minute (to get a n y d a t a on such a n oil t h e temperature must be raised and this will not indicate t h e viscosity at t h e lower temperature) ; (3) time may not be t h e proper medium for a basis of comparison.
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cone. A tachometer would indicate t h e speed a t a n y time. Temperature of test could be controlled b y carrying out t h e operation in a constant temperature room or enclosing t h e centrifuge in a case in which t h e temperature could be regulated, I t seems t o be impossible t o arrive a t any definite agreement as t o a standard instrument for viscosity while using t h e present system of time variation. It is believed t h a t a n agreement could be h a d on some modification of t h e principle suggested. The suggested form of apparatus is offered with t h e hope t h a t i t will raise discussion a n d accelerate investigation leading t o t h e adoption of a standard viscosimeter. E. I. DU FONT DE NEMOURS & COMPANY EASTERN LABORATORY. CHESTER, PA.
A CONVENlENT AUTOMATIC DEVICE FOR RAPIDLY WASHING PIPETTES B y AUBREY.VAIL FULLER Received September 11. 1917
A suggested form of viscosimeter which is shown in t h e accompanying drawing is based on a different principle and is therefore not subject t o t h e above criticism. It is described as follows: a n a r m of a centrifuge holds a cylindrical or other shaped cup having a n orifice of definite dimensions which is closed by means of a cone needle valve actuated b y a spring. A receiver is a t tached t o t h e cup t o retain any liquid passing through t h e orifice. The receiver is easily detached from t h e cup a n d b y reason of its flat bottom will be perfectly stable when placed on a balance pan. A definite quantity of oil or other liquid under examination is placed in t h e cup a n d t h e centrifuge is whizzed a t t h e desired speed when t h e valve is raised b y passing electric current through a solenoid which excites t h e soft iron core attached t o t h e valve. After a given time t h e current is shut off, whereupon t h e valve is closed b y t h e spring. A definite quantity of liquid will pass through t h e orifice in a definite period of time by varying t h e speed. Hence i t is seen t h a t temperature, time, and volume are constant and force variable. Knowing t h e length of t h e centrifuge a r m and t h e speed of rotation, t h e force required t o pass t h e liquid may be easily calculated b y t h e well-known formula. Viscosity, then, would be measured in terms of acceleration due t o gravity ( g ) , which is a rational system. The centrifuge could be driven b y a motor a n d t h e speed varied by means of a variable speed countershaft
Without doubt t h e piece of glass apparatus in daily use in quantitative analytical work most difficult t o cleanse thoroughly is t h e ordinary transfer pipette. I n order t o surmount these difficulties a n d t o render t h e ppocedure simpler and less time-consuming t h e writer has devised t h e automatic washing apparatus pictured. A is t h e inlet tube, which is connected with t h e water supply either by means of rubber tubing or by being B , B are t h e pipette permanently piped thereto. carriers, provided a t their enlarged ends with short These stoprubber stoppers bored with 3 / ~ - i n holes. . pers are fitted on their lower faces with gate valves C,C, made by cementing small squares of sheet rubber t o t h e m so as t o form a flap over t h e holes, t h e function of these valves being t o prevent t h e escape of water from t h e carrier not in actual use. D is a syphon a n d E a breather pipe, permitting t h e escape of air which would otherwise be compressed as t h e water rises in t h e carriers. The entire pipe system is supported in a copper-lined wooden t a n k , F , provided with a n outlet, G. The operation of t h e device is as follows: The supply t a p is opened until water flows from t h e syphon intermittently as in t h e familiar Soxhlet apparatus. The pipette t o be washed is then placed tip-up in one of t h e carriers. Water rises in both pipette and syphon, b u t on encountering t h e constriction a t t h e tip of t h e former, has its flow arrested, while i t freely rises t o t h e bend in t h e latter and syphonsout,emptying t h e pipette. T h e process repeats itself indefinitely, and one, or several pipettes of different sizes, may be washed simultaneously a n d without attention. I n a two-carrier apparatus as illustrated, a 5 cc. and a zoo CC. instrument may be washed side b y side. The cross-section of t h e syphon pipe is determined
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b y t h e speed of washing desired. Using 3/4-in. pipe, a 5 0 cc. pipette may be washed free from t h e ordinary K2Cr20T) on t h e third cleansing mixture (HzS04 emptying, t h e time consumed being about 20 seconds.
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in i t , a n d some asbestos-magnesia mixture, as'used for steam packing, was mixed with long-fibred asbestos and worked with water into a thick paste. This was tamped into t h e mold, as much water pressed out a s possible, and t h e whole dried upon t h e steam bath. T h e stopper held together perfectly a n d was just plastic enough, not being totally dry, t o be pressed down firmly in t h e flask. When heated, i t became hard, a n d was unaffected b y t h e fumes. On completion of t h e distillation, i t was removed with no difficulty, and on moistening became plastic enough t o be fitted into t h e flask for a second distillation. The author hopes this simple device may be useful t o others working a t a higher temperature or with chemicals which would affect a cork or rubber stopper. 2222 BANCROFT WAY BERKELEY, CALIFORNIA
A NEW FORM OF SAFETY PIPETTE B y A. S. BEHRMAN Received April 24, 1917
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It is t o be noted t h a t it is imperative in order t o obtain positive operation t h a t t h e internal diameter of the syphon bend must be t h e same as t h a t of t h e limbs. The use of t h e ordinary "return bend" is therefore excluded, and if a separate fitting is t o be employed, i t must be of t h e so-called recessed type. The detailed form of t h e apparatus may, of course, be varied t o suit conditions. I n many cases it might be found convenient t o mount t h e piping directly in t h e laboratory sink, in which event t h e overflow t a n k could be dispensed with. BIOCHEMIC DIVISION, BUREAUOF ANIMALINDUSTRY U. S. DEPARTMENT OF AGRICULTURE, WASHINGTON. D. C.
AN ASBESTOS STOPPER B y JOSEPHB. hTICHOLS
Received September 19, 1917
Having occasion t o perform a distillation involving t h e use of fuming sulfuric acid a t a temperature of about 350' C., and desiring t o use a Pyrex flaskso as t o observe t h e behavior of t h e substance, some difficulty was experienced in finding a suitable stopper. The following procedure was used with very satisfactory results: A cork of t h e proper size was obtained, a n d from i t a mold made of plaster of Paris. Two glass tubes of t h e size of t h e delivery tube and thermometer were placed
I n pipetting acids, alkalies, poisons, etc., t h e chemist is frequently confronted with t h e possibility of drawing u p some of t h e solution into his mouth. Not finding any of t h e several forms of safety pipettes on t h e market eminently satisfactory for many purposes, t h e writer finally devised t h e following simple a n d effective plan. Though t h e basic idea lends itself t o a number of modifications, t h e most compact a n d convenient one is illustrated in t h e accompanying two sketches. As will readily be seen, t h e essential feature of t h e device is a provision for permitting two inlets t o t h e pipette properone of these being connected with a source of suction, t h e other with t h e outside air. A very satisfactory arrangement is a 3-way stopcock used in conjunction with a stiff atomizer bulb, properly valved. Fig. I shows t h e device connected t o a n ordinary pipette by means of a short, stout piece of FIG. I FIG II rubber tubing. Fig. I1 shows i t made integral with a graduated pipette of t h e t y p e of Mohr's. T o operate, t h e 3-way cock is turned so as t o connect t h e pipette with t h e bulb. The pipette is then filled a little above t h e mark b y pressing a n d releasing t h e bulb one or more times, t h e bulb valves acting t o prevent t h e back flow of t h e liquid. With a stiff bulb, pipettes of even 2 j t o jo CC. capacity can usually be filled with one pressure and release of t h e bulb. The stopcock is then turned so as t o permit t h e ingress of t h e outside air, by which means t h e liquid is let down t o t h e mark, and subsequently delivered. BUREAUOF SCIENCE, MANILA, P. I.
