On the Source of Sound in the Bell Telephone. 129 



sition of HI by H 2 2 , say*, " Comparing equivalent quanti- 

 ties, it had been observed that hydric chloride increases the 

 rate of change nearly twice as much as hydric sulphate." 

 Ostwald f , by a series of experiments on specific volumes 



2H CI 



arrives at the conclusion that n Qr ^ =1*93. 



±i 2 bU 4 



Subsequently Mills and Hogarth J, after a series of experi- 

 ments on the effect of hydric chloride and sulphate on lactin, 

 considered Ostwald's result not for from the truth. Taking 

 80 as being the correct number for H 2 S0 4 , the above experi- 



2H CI 

 ments give for the ratio TT „~ the value 1*63. 

 & H 2 S0 4 



In comparing the rates of two different experiments by the 

 equation y(a + t) = b I have in every case taken the ratio jj 

 as representing the true value ; but, seeing that a is the time 

 required to perform half the oxidation, — should be equal to 



p. But this is not the case (Tables I. and II.). The reason of 



the discrepancies is, that the value of y in each case is not the 

 same when t=Q. If in two experiments we calculate the 

 times required to reduce y, say, from 10 to 5 units, and com- 

 pare them, we get the same ratio as p. 



It will be noticed that the constant a is independent of the 

 strength of the permanganate used for determining the iron. 



My best thanks are due to Dr. Frankland, in whose labora- 

 tory I had the advantage of performing the above experiments, 



XVI. Notes from the Physical Laboratory of University College, 

 Bristol. By Prof. Silvanus P. Thompson, B.A., D.Sc.§ 



I. On the Source of Sound in the Bell Telephone. 



THE question has been at various times and in sundry 

 places discussed whether the sounds emitted by the Bell 

 telephone, when used as a receiver of currents, are caused by 

 molecular vibrations in the instrument, or are due to vibra- 

 tions executed by the thin iron disk as a whole. The former 



* Phil. Trans. 1867, p. 134. 

 t Journ. prakt. Chein. n. F. xvi. p. 419. 

 \ Proc. Roy. Soc. vol. xxviii. p. 272. 



§ Communicated bv the Physical Society, having been read at the 

 Meeting on April 20, 1879. 



