Three laboratory experiments for students in beginning chemistry are here submitted in the hope that they may be found useful to other teachers of chemistry as they have been helpful in the author\u27s laboratory

Hendrixson, W. S.

English

University of Northern Iowa

Proceedings of the Iowa Academy of Science Volume 25 Annual Issue Article 45 1918 Some Improved Laboratory Methods W. S. Hendrixson Grinnell College Copyright ©1918 Iowa Academy of Science, Inc. Follow this and additional works at: https://scholarworks.uni.edu/pias Recommended Citation Hendrixson, W. S. (1918) "Some Improved Laboratory Methods," Proceedings of the Iowa Academy of Science, 25(1), 497-500. Available at: https://scholarworks.uni.edu/pias/vol25/iss1/45 This Research is brought to you for free and open access by the Iowa Academy of Science at UNI ScholarWorks. It has been accepted for inclusion in Proceedings of the Iowa Academy of Science by an authorized editor of UNI ScholarWorks. For more information, please contact scholarworks@uni.edu. SOME IMPROVED LABORATORY METHODS.W. S. HENDRIXSON.Three laboratory experiments for students in beginning chemistry are here submitted in the hope ihat they may be found useful to other teachers of chemistry as they have been helpful in.the author's lalboratory.1. Bleaching powder, potassium hypocMorite and potassiumchlorate may be prepared in one experiment by use of the apparatus illustrated in figure 167. In the flask u evolved chlorineFig. 167in the usual way by use of manganese dioxide and hydrochloricacid. The gas passes into the bottle which contains diluted sul-furic acid, in the proportion, 1 of water to 4 of acid by volume.Acid of this concentration will absorb most of the water andgaseous hydrochloric acid. The horizontal test tube containsabout three grams of lime spread evenly throughout the length.The excess of chlorine passes from this tube into the second testtube which contains a solution of five grams of potassium hydroxide in fifteen c.c. of water. This tube must be kept cool during the first part of the operation. After two to three liters ofchlorine have been passed through about one-third of the con32 1Hendrixson: Some Improved Laboratory MethodsPublished by UNI ScholarWorks, 19184!(8 IOWA ACADEMY OF SCIENCE VOL. XXV, 1918tents of tube two should be set aside as a solution of potassiumhypochlorite. The remainder is heated to boiling and the streamof chlorine passed through it for a few moments. One to twograms of potassium chlorate will crystallize out on cooling, andit should be purified 'by crystallization. The characteristic reactions of 'both salts should be.brought out by suitable tests.2. The preparation of Sulfwric Acid :—Probably most teachers who have used the usual cumbersome apparatus for laboratory illustration have found it disappointing and wanting in reality. The apparatus shown in figure 168 has been successfullyused in this laboratory.•oFig. 168The great European war has made difficult or impossible thesecuring of good combustion tu'bing. Ignition tubes of hardglass have always been expensive and hard to get ready made.For them, the writer has substituted tubes made of half inch gaspipe for general use in experiments requiring high temperatures,such as in the preparation of nitrogen dioxide by heating lead nitrate, methane, oxygen from potassium chlorate alone, ammonia.In all these cases is used a piece of pipe ten inches long cappedat one end while the other end is reamed to take smoothly a rulb-ber stopper.In the ignition tube, figure 168, is placed tea to twenty gramsof granulated iron pyrite. The test tube contains about three c.c.of concentrated nitric acid. The larger bottle may be used withonly its walls wet if it is desired to produce the "chamber crystals"; otherwise it should have its walls wet, and a few c.c. ofwater on the bottom. The second bottle has an alkaline solutionto absorb the excess of gases, but is really not necessary. Air isforced through from the pressure system. If no such system isavailable the exhaust system or filtering pumps may be used. Onelamp is sufficient. Once the conibustion is started little external2Proceedings of the Iowa Academy of Science, Vol. 25 [1918], No. 1, Art. 45https://scholarworks.uni.edu/pias/vol25/iss1/45SOME IMPROVED LABORATORY METHODS 499heat is required, and too high a temperature drives off unburnedsulfur.At the end of about twenty minutes the contents of the largerbottle and the test tube with rinsings should be evaporated tillthe fumes of sulfurie acid appear. A run of even ten minuteswill give three to four grams of concentrated sulfurie acid.3. Conductivity of Electrolytes.—It is very desirable to haveevery beginning student do some work on electrical conductivityand electrolysis. Probably every teacher whj has tried to havelarge numbers of beginners do work in this line has felt the needof a suitable conductivity cell. A cell with platinum electrodesFig. 169at the present price of platinum is practically out of the question, and we are limited to carbon for this purpose.A conductivity cell which the writer has used with greatsatisfaction is shown in figure 169. The only merit he claimsis the discovery that the spring binding post or connector of theFahnestock Electric Company, Long Island City, New York,has just the right bend to clamp firmly a three-eighth carbonrod. This connector and wire as shown makes a perfect unionof the rod and the source of electricity : The cell may be used inmany ways. Delivery tubes may be attached to the side urmsof the U tube and the cell used to illustrate the so-called electrolysis of water, test tubes of the same diameter serving tocollect the hydrogen and oxygen. Copper may be deposited onthe negative electrode.3Hendrixson: Some Improved Laboratory MethodsPublished by UNI ScholarWorks, 1918500 IOWA ACADEMY OF SCIENCE VOL. XXV, 1918In using the cell in comparative conductivity in this laboratory several taps are provided. At each is a lamp socket sothat the direct lighting current may be cut down with lampsof various resistances. The glow of the lamp itself gives a roughquantitative measurement of the strength of current transmittedby the cell, but in addition it is better to introduce ammetersreading as low as one one-hundredth of an ampere. In eachtest the cell is filled to the same height as indicated by somesuitable mark, such as gummed paper. Tenth normal solutionsare made up in quantity, for general use. The following havebeen found instructive : hydrochloric acid, sodium chloride, aceticacid, sodium acetate, ammonia, sodium hydroxide, distilled andordinary tap water.The experiment offers a good opportunity for the review ofelectrical terms and relations. Knowing the wattage of thelamp and the electromotive force of the current the resistance ofthe lamp may be calculated. The current transmitted by thelamp alone may ibe calculated and the result verified by the ammeter. From the current transmitted by both lamp and cell theresistance and conductivity of the solution in the cell may becalculated.DEPARTMENT OF CHEMISTRY,GRINNELL COLLEGE.4Proceedings of the Iowa Academy of Science, Vol. 25 [1918], No. 1, Art. 45https://scholarworks.uni.edu/pias/vol25/iss1/45

Some Improved Laboratory Methods

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Some Improved Laboratory Methods

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