48 Prof. J. P. Cooke on Lecture Experiments. 



Wertheim finds 0*79 for carbonic acid and 3*81 for hydrogen. 



A tube filled with air through which ether had passed gave 

 35 waves instead of 32 ; that is, 0*91 for the velocity of sound 

 in air saturated with ether. 



The following experiment was made on the influence of tem- 

 perature on the velocity of sound. The apparatus with two glass 

 tubes gave as the mean of several measurements 35*743 millims. 

 for the length of half an air-wave at 14° C. When the outside 

 tube was heated to about 26° C, 36*576 millims. was found to 

 be the length. Anew determination at 14° gave again 35*797 

 millims. j while at 30° 37*357 millims. were found. 



Warming the sounding glass tube had thus scarcely any in- 

 fluence on the length of the air-wave, and thus left almost un- 

 altered the velocity of sound in glass. 



IV. On certain Lecture- experiments, and on a New Form of Eu- 

 diometer. By Josiah P. Cooke, Jun., of Harvard College*. 



THE 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 lec- 

 ture-room are eagerly sought by every teacher of the science. 

 The many new and interesting experiments devised for this pur- 

 pose by Professor Hofmann, first described in the Journal of the 

 Chemical Society of London (Ser 2. vol. iii. p. 156), and subse- 

 quently made still more widely known through his admirable 

 ' Introduction to Modern Chemistry/ leave little to be desired 

 so far as regards accuracy of results or elegance of illustration. 

 But these experiments require for the most part a delicacy of 

 manipulation which is incompatible with the hurry of the lec- 

 ture-room, and a skill in glass-blowing which can rarely be at- 

 tained. Hence, while seeking the same end as Professor Hof- 

 mann, but with less ample appliances, 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 analytical methods they may not always be as accu- 

 rate as those of that eminent chemist. 



Many of the methods described in this paper are alone ren- 

 dered possible by the application of vulcanized rubber stoppers 

 in the construction of the required apparatus. Hitherto these 

 have not been made of good quality in this country ; and those 

 imported from Europe were very costly, and could only be ob- 



* From a separate reprint from Silliman's American Journal, communi- 

 cated by the Author, to whose kindness we are also indebted for the 

 woodcuts. 



