THE 



AMERICAN JOURNAL OF SCIENCE 



[FOURTH SERIES.] 



Art. XXXVI. — Several Lecture Experiments in Elementary 

 Physics ; by D. Albert Kreider. 



Believing that it may prove of service to other teachers of 

 the subject, the author has been persuaded to put into print 

 the following description of some apparatus and experiments 

 which have been yielding gratifying results for a number of 

 years. It represents, in part, a development here which is the 

 result of continuous effort to simplify and to expedite experi- 

 mental demonstrations ; to enable the student, as well as the 

 demonstrator, to see distinctly all details of both the manipula- 

 tion and the result of experiments ; and primarily, wherever 

 possible, to provide for the student's personal observation of 

 all numerical readings. 



1. A Projection Cell. — With the projection cell and its 

 equipment, illustrated in figure 1, a few minutes suffice to 

 demonstrate the essential construction, the chemical action and 

 the voltage of several types of cells, and all of the methods of 

 depolarization. The cell shown was originally cut .from a 

 commercial four-ounce bottle of rectangular section and has 

 proved sufficiently satisfactory to be continued in service ever 

 since. A bottle, when free from conspicuous defects, avoids 

 the annoyance of leaky cells and, despite considerable irregu- 

 larities in the thickness of the glass, affords projections which 

 are perfectly distinct. The porous partition between the com- 

 partments A and B of the cell was cut from a chemist's 

 unglazed porcelain drying dish ; the flange on which the plate 

 normally rested serving to close off half of the neck of the 

 bottle. It was joined to the glass by a paraffin seal, with pre- 

 cautions against excessive clogging of the pores. A glass 

 tube, provided with a stopcock and long enough to clear the 

 side of the projection lantern, was attached to the neck of the 



Am. Jour. Sci. — Fourth Series, Vol. XXXII, No. 191.— November, 1911. 

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