THE EXHIBIT AS A SUPPLEMENTARY METHOD�II. FORMS OF CALCIUM CARBONATE

BY HAROLD J. ABRAHAMSSimon Gratz High School, Philadelphia, Pennsylvania

A previous article in SCHOOL SCIENCE AND MATHEMATICS1discussed the use of exhibits as a method of presenting instruc-tional material otherwise crowded out of the science curriculaof high schools. Not only to widen the applicability of thismethod, but also to maintain student interest, the suggestionwas made that exhibits be replaced frequently. In harmonywith this idea, we present the results of a second project alongthese lines.

Calcium carbonate occurs in great abundance in such a widevariety of forms as to be a source of never-ending wonder. Someof these forms have properties which are either unique, ^mys-terious,^ or intriguing. Teachers can easily recall the open-eyedamazement of young students when they first realize that dull,apparently shapeless chalk, glistening crystals of marble, trans-parent, doubly refracting calcite and various marine shells are,in the main, chemically identical. The ease with which its varie-ties can be used to emphasize the fact that different forms of thesame chemical compound may possess widely contrasting prop-erties therefore makes calcium carbonate an ideal subject fortreatment by the "exhibit77 method.The present exhibit was set up in two museum cases as

follows:Inverted specimen jars containing bright calcium shavings,

powdered charcoal and oxygen gas respectively were placed atthe rear of each of the two cases. From a card, bearing thewords "Calcium Carbonate,77 in front of each set of the threeelements, red ribbons led off to cards bearing the captions"Marble,77 "Calcite,77 "Limestone77 and "Coral77 in Case I and"Eggs,77 "Mollusks,77 "Crustacea,77 "Echinoderms77 and "Pro-tozoa77 in Case II. From each of these nine headings, a redthread ran to the front edge of the case and along these threadswere placed the appropriate specimens exemplifying the cap-tions. Thus location of a specimen either upon or near a threadclassified it at once for the observer as belonging to the maindivision indicated by the caption at the top of the thread. The

1 "The Exhibit As A Supplementary Method�Crystallography," December 1936.

1061

1062 SCHOOL SCIENCE AND MATHEMATICS

specimens in the two cases were thus divided in the main ac-cording to whether they had their immediate origin in theinanimate or animate world.

Small tags were prepared for those specimens having specificnames or unusual interest. In Case I, for example, a specimenof limestone taken from the Great Pyramid of Cheops, nearCairo, was so labelled, and its marine shell origin emphasizedby placing a magnifier above it to facilitate inspection. A pieceof newsprint was placed under the specimen of doubly-refract-

CASE I

ing calcite, to draw attention to its unique property. Near thisspecimen was a card bearing the words ^Everything appearsdouble.^ A card under the ^onyx^ read ^Real onyx is silicondioxide.^ Among the corals one specimen was unusual. It con-sisted of a coral growth upon a glass bottle found on the beachat a seaside resort.The specimens in Case II were intended to make association

in the students? minds between calcium carbonate and its useby living forms. To introduce a note of variety and thus over-come too evident repetition, the egg division was made up of aseries of eggs graduated in size, from the gigantic one of theostrich to the small one of the turtle. Specimens in the molluskdivision, which attracted much attention and elicited comment.

FORMS OF CALCIUM CARBONATE 1063

were a piece of ^mother of pearl" with perforations showingwhere buttons had been punched from it by a machine, a neck-lace made of marine snail shells and a long oyster shell to whichnumerous smaller shells were attached. Three small crab moltsunder the Crustacea caption stimulated much interest, as didthe exoskeletons of several small crayfish. The calcareous re-mains of a very tiny king crab amused many students. As anadditional attempt to implant some idea of the important roleplayed by minute living forms in building up vast inanimate

CASE II

things, a microscope focused upon Fusilina was placed underthe Protozoa caption, next to a specimen of ^limestone inprocess of formation.5’The beauty of form and color attainable by such a collection

of mineral and marine specimens must be left to the imagina-tion. The accompanying photographs2 will give merely an ideaof the arrangement of materials. Above the exhibit was placeda typewritten plaque reading as follows:

"A Various Language"Nothing in the wildest imaginative writings of man is more surprising

thanNature^s cunning. From the same substance she can fashionboth livingtissue, too small to be seen by the naked eye, and ridges of limestone, so

2 Grateful acknowledgment is herewith made to Mr. Mark H. Hagmann of our Mathematics de-partment for the accompanying photographs.

1064 SCHOOL SCIENCE AND MATHEMATICS

immense as to be visible at a distance of many miles. Her art enables herto build yesterday^s living matter into submerged mountains of coral,upon which large ocean liners often dash themselves into bits. Yet she canuse the same material to a more kindly purpose�in her concern for thepain of one of her creatures, the lowly pearl-oyster, she sends forth a fluidto relieve the irritations caused by a grain of sand. Thus is formed thehighly prized pearl.

Often she fashions tiny shells of the same chemical substance, and thenbuilds these into mounds so broad and high that they become vast landareas, when the ocean recedes. The white chalk cliffs of England, which,because of their color, caused the ancients to call that country Albion,were formed in this way.

Chalk and pearl, . . . coral and marble, . . . microscopic Foraminiferaand gigantic hills of travertine, . . . egg shell encasing life and limestonepyramids enclosing the dead remains of the "late" Pharoah Cheops, . . .reefs to destroy man and caves to shelter him . . . living, moving creaturesand inanimate, transparent calcite . . . behold the real Jekyll and Hyde!

Everything shown in these display cases is calcium carbonate, a com-pound consisting of one "part" calcium, one "part" carbon and three"parts" oxygen. Calcium carbonate is, next to quartz, the most widelydistributed of all minerals. When we consider the great variety of formswhich calcium carbonate can assume, we do not wonder that a great manhas written:

"To him, who in the love of nature holdsCommunion with her visible forms, she speaksA various language ..."

LIST or MATERIALS IN THE EXHIBIT

Case ISpecimens ofCalcium, Carbon and Oxygen

MarbleCalcite

BiancoAnticoS^?0 f ,�Giallo di SiennaDoubly^^SBandillioDog Tooth SParMisto di CarraraSa^rS1’ crystamne varieties

clyomno ,.. .AragoniteBroccatello di SpagmaLimestoneBlore di France-ni T � ..T^�,- j- T?BlueLimestoneRosso de France^^ ^ ^ ^Pora Venere TypeI)p^ f^om the Great Pyramid ofPorta Venere (Type II)Cheops(-fossil shells)^ntstalicite (P011^"Onyx" (true onyx is silicon diox- Coral^le) Tv/r 1-1Branching�several varietiesWhite MarbleBrainBlack MarbleMushroom�two varietiesYellow pink veinedPropellerMarble dishCarved Coral jewelry

FORMS OF CALCIUM CARBONATE 1065

Case IISpecimens of Calcium, Carbon and Oxygen

Eggs CrustaceaOstrich crab moltsPheasant Edible blue crabHen ^^y crabTurtle Fiddler crabWren Hermit crabCanary Crayfish

BarnaclesMollusks Spider crabAbalone shells (2) King CrabsOyster� shell Small and largeLand snailsClam shell EchinodermsMussel�shell See urchin (spines removed)Mother of Pearl (holes punched Sea urchin (with spines)

through) Sand dollarRazor clam StarfishConch shells Brittle starMarine snails ProtozoaScallop shell ^ ^ ^ formation ofCoquma ^^Baroque Pearls Limestone in process of forming

Fossil FusilinaSlide of Fusilina under microscope

The most pronounced reaction evoked in the majority of stu-dents by the exhibit was a gratifying appreciation of the beautyof form and color possessed by the biological portion of theexhibit. To those who may have failed to grasp the main ob-jective of the exhibit, the aesthetic appeal appeared sufficientlystrong to have justified the experiment for this indirect in-fluence upon them. The more thoughtful students expressedsurprise at discovering a relationship between the realms of theanimate and inanimate. Others were surprised to find that cer-tain familiar marine forms belonged to one phylum rather thanto another, leading to the thought that exhibits might aid inpresenting phyla in the study of zoology.

GLACIERGreat forests wiped out by glaciers only a few thousand years ago have

just been uncovered by a small recession of the Alaskan coastal glaciers,according to findings reported by William S. Cooper, University of Min-nesota glaciologist, in the Geographical Review. Shortly after the last greatice age, which ended only 20,000 years ago, the ice receded far up thevalleys on the Alaskan coast, and great forests grew up on the well-wateredvalley floors. A period of cooling only a score of centuries ago caused aglacial readvance, and the forests were buried under frozen gravels andice. Recently, the ice has melted, and the stumps of these ancient foresttrees are again exposed to the air. This recent retreat began only about 200years ago, according to evidence supplied by rings in frees growing on theglacial deposits.