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
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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.
