U niversity
of
O regon M on th ly
33
T h e follow ing is a sam ple of th e re g u la r w ork in th e sec
ond year in th e P h y sical L a b o ra to ry , bein g ra th e r full notes
w ith som e ex p lanations, on one of th e sim pler exp erim en ts of
the course in P hysical M easurem ents. A high degree of
accuracy is expected.
Specific Gravity of Air.
A n o rd in a ry electric lig h t bulb contains so little air th a t
th e vacuum m ay be reg ard ed as v e ry n early com plete. O ne
of th ese bulbs w as w eighed carefully, th en th e point a t the
low er end w as snipped off, a d m ittin g air. T h e bulb, to g e th e r
w ith the. broken pieces of glass, w as again w eighed. T h e
difference betw een the tw o w eighings m u st be th e w eig h t of
th e contained air. A sm all piece of w ax w as now p u t on th e
scales and th e w eig h t of th e bulb and w ax w as determ ined.
T h e n by m eans of a ru b b er tu b e and a glass nozzle, th e bulb
w as filled w ith gas from th e gas m a in s ; th e piece of w ax
w as p u t over th e sm all o p en in g -to keep th e gas from fl6w ing
out. T h e bulb full of gas w as th en w ieghed, so th a t all the
d a ta w ere at h an d for co m p u tin g the w eig h t of the gas and of
th e air. I t rem ained to find th e volum e of the bulb. T h is
w as done by filling th e bulb w ith w a te r by m eans of th e g lass
nozzle and ru b b e r tu b e, and th en w eig h in g th e bulb w ith th e
contained w ater. T h e n u m b er of gram s of w a te r w ould give
th e n um ber of cubic cen tim eters in th e bulb, since by defini
tion th e gram is th e w eig h t of a cubic cen tim eter of w ater.
T h e w eighings to determ ine the am o u n t of w a te r contained in
the bulb, and hence th e volum e, w ere m ade on larg e r scales