A DEMONSTRATION ON LABORATORYTECHNIQUE IN HIGH SCHOOL

CHEMISTRY

BY ERWIN PFEFFERKORNWanfun High School, Waupun, Wisconsin

Most students have seen their instructors perform experi-ments and use such apparatus as is found in the average chem-istry students locker. When the student himself uses the ap-paratus he lacks the technique that was unobserved when hesaw the materials used. It is well that the students be madeacquainted with simple laboratory procedures before they aresent into the laboratory. It is to avoid costly mistakes in theuse of apparatus as well as loss of time due to personal injurythat the following demonstration may well precede initiationinto laboratory work.

Rather than write up the demonstration in the conventionalexperiment form, the following discourse takes up the subjectsas demonstrated by the instructor as well as related questionsand associated topics. Many of the topics follow each other asa natural sequence as a result of using previous apparatus.1. BUNSEN BURNER.

All students know that to light a Bunsen Burner we openthe gas jet and light the burner. Sometimes the gas pressure istoo high and the sudden release of gas blows out the match.It is best to draw the lighted match downward toward the topside of the burner.When a burner strikes back, it is burning at the base with a

hissing sound and the gas should then be turned off immedi-ately. Continued burning in the base of the burner results inthe base getting so hot that the rubber connection begins toburn. Readjust the gas and air intakes and relight the burnerso it burns with a quiet flame.2. CUTTING GLASS TUBING AND RODS.

Either glass tubing or rods can be conveniently cut by takinga three-cornered file and scratching the glass at the desiredplace. With the scratch up, lay the tubing on the file so that thescratch is directly above the file corner. Apply pressure to eitherside of the scratch and the glass will break at the scratch.Another convenient way of separating the glass at the de-

sired scratch is by placing the thumb nails just opposite thescratch and applying pressure to break the tubing. The broken

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CHEMISTRY DEMONSTRATIONS 477

ends of the tubing are very sharp. How can they be rounded?3. FIRE-POLISHING.Heat the end of a glass tube in the oxidizing part of a flame

until the flame begins to be distinctly colored yellow by thetube. Do not overheat, as continued heating will eventuallyclose up the hole and render the glass useless as a tube. Whydoes heating eliminate the sharp edges? (Look up in a physicsbook on the subject of surface tension.)A glass rod can be fire-polished in the same manner as the

glass tube. Why does it take much longer? The glass rod youhave now fire-polished can be used as a stirring rod. A piece ofglass tubing is unfit as a stirring rod because the inside of thetubing cannot be conveniently cleaned.4. INSERTING GLASS TUBING, RODS, AND THISTLE TUBES INTO

STOPPERS.Serious injury may result if dry glass tubing is pushed into a

dry rubber stopper. Wet the fire-polished tubing in water, andif possible, use the tubing as a pipette and let the water runinto the stopper hole. This will lubricate the stopper and pre-vent the tubing from being broken. Apply the turning pressurewith the hands as near as possible to the stopper.When tubing is to be inserted into a two-hole stopper, insert

the shortest one first. If a thistle tube is to fill the second hole,grasp the thistle tube by the wetted stem near the stopper androtate. It is sometimes advisable to take the thistle tube outof the stopper and rewet for a second time if the tube is to beinserted nearly full length in a stopper.5. REMOVING STOPPERS FROM TUBING, RODS, ETC.

Especially when stoppers become hot, they will tend to stickto the inserted rod or tubing. Always remove tubing from stop-pers at the close of an experiment. When it is necessary to re-move a ^stuck57 tube, do not try to twist it out�set the tubingat right angles to the table and push down by applying pressureparallel with the tubing and with the thumbs on the stuckstopper. If this method fails, discard the stopper to avoidinjury.6. PUTTING RUBBER TUBING ON GLASS RODS AND TUBING.

In general, the same procedure applies to rubber tubing asto rubber stoppers. The glass rod or tubing should be fire-polished and wet before it is inserted into rubber tubing. Whenrubber tubing is put on a glass tube somewhat larger than thetubing diameter, e.g., distilling tube connection, it is best to

478 SCHOOL SCIENCE AND MATHEMATICS

turn the tubing inside out for a quarter of an inch and then letthe ^snapping back^ of the rubber tubing aid in getting thetubing over the glass rod or tube.7. RUBBER AND CORK STOPPERS.A simple method by which hardened rubber stoppers can be

softened is by placing the stoppers on the floor and ^rolling’?them underfoot with considerable pressure. Commercial ap-paratus is available for this purpose, but for the average highschool laboratory the simple method will suffice.When cork borers are used, it is best from the standpoint of

stability to start boring on the small end of the cork.8. USING LIQUID REAGENTS.

(a) Removing Glass Stoppers.Granting that the stopper is not stuck, place the hand,

palm up, over the stopper so the stopper can be liftedup by placing it between the fingers. This method keepsthe stopper clean and off the table. A dirty stopper willthen not be put back into the bottle and neither will thetable or clothes be ruined by corrosive chemicals. Bythis method both hands are free to manipulate ap-paratus, though the stopper is held between the Angers.

(b) Pouring from Reagent Bottles.Grasp the bottle so that the label is up when you pour.

What effect does improper technique in pouring have onpaper labels?Keep the graduate or receiving vessel at near eye

level for accuracy in measurement.Avoid resting on or touching the receiving vessel with

the container from which you are pouring as this maycontaminate the original liquid.

(c) Excess Liquids.Don^t have any! Be accurate in your first measure-

ment, but if you do, do not pour them back as you mightspoil the purity of the original liquid. Test tubes andgraduates too often are not clean.

(d) Diluting Acids.Remember the rule�Always pour acid into water.

Reversing this will cause the acid to spatter upon thesudden release of heat.

9. WEIGHING CHEMICALS.If two chemicals, e.g., MnOa and KClOs, are to be weighed,

zero your scale to the weight of the paper on which the chemicals

PROBLEM DEPARTMENT 479

are to be placed. Both chemicals can be weighed on the samepaper, if after weighing out of say 3 grams of Mn02, the scaleslider is pushed ahead 6 grams to accommodate the KClOs.This saves time when a limited number of scales is available.

PROBLEM DEPARTMENTCONDUCTED BY G. H. JAMISON

State Teachers College, Kirksville, Mo.

This department aims to provide problems of varying degrees of difficultywhich will interest anyone engaged in the study of mathematics.

All readers are invited to propose problems and to solve problems here pro-posed. Drawings to illustrate the problems should be well done in India ink.Problems and solutions will be credited to their authors. Each solution, orproposed problem, sent to the Editor should have the author’s name intro-ducing the problem or solution as on the following pages.The editor of the department desires to serve its readers by making it

interesting and helpful to them. Address suggestions and problems to G. H.Jamison, State Teachers College, Kirksville, Missouri.

SOLUTIONS AND PROBLEMSNote. Persons sending in solutions and submitting problems for

solutions should observe the following instructions.1. Drawings in India ink should be on a separate page from the

solution.2. Give the solution to the problem which you propose if you have

one and also the source and any known references to it.3. In general when several solutions are correct, the ones submitted

in the best form will be used.

LATE SOLUTIONS1475. Isadore Chertojf, Bayonne, N. Y.

1472, 3, 7. G. S. N. Ayyar, Tiruvilwamala, India.

1478. Proposed by Cecil B. Read, Wichita, Kansas.Which has the greater ratio, (x’2-{-y2’)/(x-{-y) or (x2�y2)/(x�y), if x and

y are positive numbers?

Solution by Harold Sogin, Student, Tilden Tech, H. S., Chicago, III.(x2-y2)/(x-y)>(x2+y2)/(x+y).

For if (x2-{-y2)/(x+y) >(x2-y2)/(x-y)Then (x2+y2) / {x-[-y) >(x+y) or

^2.^2;>^2_i_2^+y2and Q>2xywhich is impossible since x and y are positive.

Solutions were also offered by Charles W. Trigg, Los Angeles, IsadoreChertoff, Bayonne, N. J., A. R. Haynes, Tacoma, Wash., and the pro-poser.