J. P. Cooke, Jr., on Lecture Experiments. 189 
Art. XVIII.—On certain Lecture Experiments, and on a new i 
jorm of Kudiometer ; by Jos1aH P. Cooks, Jr. 
Tue laws of combination by volume fill such an important 
place in our modern chemical philosophy that simple methods 
of illustrating these fundamental principles in the lecture room 
are eagerly sought by every teacher of the science. The many 
hew and interesting experiments devised for this purpose by 
‘of. Hofmann, first described in the Journal of the Chemical 
Society of London (Ser. II, vol. iii, page 156), and subsequent 
made still more widely known through his admirable “ Intro- 
duction to Modern Chemistry,” leave little to be desired so far 
a8 regards accuracy of results or elegance of illustration. But 
these experiments require for the most part a delicacy of man- 
ipulation, which is incompatible with the hurry of the lecture 
Toom, and a skill in glass-blowing which can rarely be attained 
or commanded by our American teachers. Hence while seek- 
Ing the same end as Professor Hofmann, but with less ample 
’ppliances, the author has devised for his own lecture-room 
methods of illustrating the same principles, which require less — 
delicate apparatus and less careful attention, although as analyt- 
-Ical methods they may not always be as accurate as those of 
this eminent German chemist. Following also the recommend- 
ation of Prof. Hofmann in the article just referred to, the author 
publishes his methods with the hope that they may serve to bring 
illustrations of these fundamental laws of chemistry within 
the reach of the great body of teachers in this country 
‘any of the methods described in this paper are alone ren- 
dered possible by the application of vulcanized rubber stoppers 
1 the construction of the required apparatus. Hitherto these 
i rolls of the sizes named above have been — 
found to be orn bege arhes) ealeenec or to onderel any 
ost universall licable, but they can be made to order of 2 
