A GLASS MANOMETER for LABORATORY USE by STUDENTS in PHYSICAL CHEMISTRY T. E. PHIPPS, M. L. SPEALMAN,
AND
T. G . COOKE
University of Illinois, Urbana, Illinois
Detailed instructions are offered for the construction of an all-glass manometer of the type referred to herein as the "sickle" type. Attalion is called to possible uses of suck a gage in ex@rimentnl work.
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HE NEED for an all-glass manometer relatively simple in construction and operation has doubtless been apparent to many teachers of laboratory courses in physical chemistry. The mauometer described herein is not original with the authors, having been used by several investigators. However, no detailed account of a method of construction bas appeared in the literature, so far as the authors q e aware. The success with which the device has beenused in a laboratory course in physical chemistry a t the University of Illinois has encouraged them to think that constructional details of the manometer would be of interest to others. A brief description of various all-glass gages is given by F. Daniels (1). The gage attributed to C. G. Jackson (2) and G. E. Gibson (3) is similar to the "sickle" gage used by the present authors. In modern published work it is found that gages of this type have been employed by several pbotochemists. For example, R. G. W. Norrish (4) used it in a photochemical study of the union of hydrogen and chlorine; E. Ponsaerts (5) in studying the radiochemical synthesis of ammonia; and H. P. Smith, W. A. Noyes, Jr., and E. J. Hart (6) in their photochemical studies. The latter refer to it as a "ovrex eaee of the Bodenstein type." It appears, however, that the sickle gage should be aedited to Gibson, since Bodenstein's original A,
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F I G U R E ~.-INITIAI.
STEPS I N FIIBRIcATISG THC GLASSGAGR
RGL'RE ~-INTERMED~FABRICATING ATE STEPSIN THE ASS GAGH
gage (7) was of a coil type. Bodenstein and also F. M. G. Johnson (8) have aedited the idea of the spiral gage to E. Ladenberg and E. Lehmanu (9). Details of the method of construction of the gages used in this laboratory follow. A pyrex tube about 6 to 8 mm. in outside diameter and of standard wall thickness is cleaned with wet plugs of cotton, rinsed, and dried. A piece about 30 cm. long is iire-polished a t one end and provided with a lightweight rubber blowine tube which is held in the mouth of tlhe operator during the next step. The free end is
Eleven students who made A in 111 made the same grade in 112. Nineteen students who received a grade of A in 111 made a B in 112, etc.
Grade in111
Toid
Gm&r in 112 B C D
A
P
Numb. of Sludrnlr in I l l
--
Total
32
112
182
64
29
409
825
TABLE 2 GRADES
Total
MADS IN Cnamsrsv 102 A N D 112
A
B
15
17
Grodts in 112 C D
P
Told
Numbr of SIrdtnls in 102
7
5
72
211
28
TABLE 3
G R A D BMADS ~ BY k c S W D B N IN ~CHBX~STRY ~ 112
A 79
B 204
'C 327
D 113
P
Told
60
783
From the above tables it may be seen that the failures among students in 112 who had passed 111 were 7.1 per cent., and the failures among students in 112 who had passed 102 were 6.9 per cent. Very few students, however, who had low grades in 102 continued with our more advanced chemistry course. Of all the students completing 102 who continued with 112 only 6.9 per
cent. were D students in our more elementary course. At the same time, of the students completing 111 who continued with 112, there were 17.8 per cent. who were D students in the elementary course. These considerations would cause one to expect a much higher percentage of failures among the students of the latter group. From the tables the following computations were made:
. .. . .. ..... . .. . . ... .. .. . .. ..
~ ~ e r a of g eall students in 111... . . . . . , . . . . Average in 111 of stndents who later took 112.. Average of all students in 102.. ... . ~ v e r a g ein 102 of students who later took 112.. 5. Average in 112 of all students, including transfers.. 0. Average in I12 of students who completed 111.. 7. ~ v e r a g ein 112 of students who completed 102.. 8. Coefficient of correlation, 111-112 group (Table 1) 9. Coefficient of correlation, 102.112 group (Table 2)
1. 2. 3. 4.
1.91 grade points* 2.21 " " " 2.17 " 2.65 " " 2.16 " " 2.15 " " 2.42 *' " 0.49 * 0.05 0.67 * 0.03
The average grade points as listed above seem to be significant from the following standpoints: (1) The difference between the average grade points in 111 and 112 is 2.21-2.16 for students who have had both courses, or a drop in average of 0.03 grade points. (2) The difference between the average grade points in 102 and 112 is 2.65-2.42 for the students who have had these courses, or a drop of 0.23 grade points. Although the coefficient of correlation for the 102-112 group is higher than that for the 111-llQroup, the difference is probably not significant. In view of the above information we feel justified in considering the preparation of students who have had high-school chemistry and our one-semester general chemistry course as equivalent to that of the students who have had a year of college chemistry with US. * Grade points are as follows:~, .. A, 4; B,3; C,2; D, 1; F, 0.
An EXPERIMENT on CHEMICAL
EQUILIBRIUM-for BEGINNERS LAWRENCE P. EBLIN The Ohio State University, Columbus, Ohio
Complete directions are g i m for an experiment on chemical equilibrium to be performed by students of general chemistry. An introduction includes a statement of why such an experiment has been designed, and a summary of the purposes which it serves. The experiment has been used for two years at Ohio State i n classes which have had high-school chemistry.
A
LL TEACHERS of chemistry will probably agree that a true appreciation of the nature of chemical equilibrium is necessary for the understanding of chemical phenomena. However, the begin-
ning student is often expected to gain this appreciation from a mere study of those portions of his text in which equilibrium is discussed. There seems to be a sad dearth of laboratory experiments designed for the express purpose of providing the student with a concrete basis on which to construct his concept of chemical equilibrium. Experience with freshmen a t this university has resulted in the belief that the exercise on equilibrium in the laboratory manual of McPherson, Henderson, and Evans' could be expanded and revised to meet the purposes which have evolved from our MCPRER~ON, HENDERSON, AND EVANS, "Laboratory manual
to accompany the fourth edition of 'A course in general chemistry,' " Ginn 81 Company, Boston, 1934, p. 87.
