Energy and Apparent Intensity of Sounds of different Pitch. 381 



and partly because this matter has been looked upon by manu- 

 facturers as being of a merely secondary nature. But I was led 

 to inquire into it in a more serious manner from the fact of 

 having seen much acid returned to the manufacturers as being 

 unfit for use owing to the presence (supposed !) of iron, while all 

 the disturbance arose from the presence of this extremely diffi- 

 cult-to-be-got-rid-of substance, arsenic. In several instances 

 also which have come to my notice in the cases of manufacturers 

 of ammonium sulphate, many hundred pounds' worth of mate- 

 rial has been lost through the use of acid containing this im- 

 purity, while the unfortunate makers were vainly searching for 

 their old enemy, iron. 



The importance of examination for the presence of arsenic can 

 scarcely be too strongly urged upon the manufacturers of such 

 materials. In conclusion let me say that, as far as my own ex- 

 perience goes, the use of sodium sulphide answers the purpose 

 to a more perfect degree than any other process. Of course 

 many improvements can be made upon the method of application 

 given above ; yet, for a rough but satisfactory method, I have 

 found it sufficiently accurate. 



XLV. On an Experimental Determination of the Relation between 

 the Energy and Apparent Intensity of Sounds of different Pitch. 

 %R. H. M. BosANQUET, M.A., F.C.S., F.R.A.S., Fellow of 

 St. John^s College^ Oxford. 



To the Editors of the Philosophical Magazine and Journal, 

 Gentlemen, 



THE comparison of the intensities of sounds of different pitch 

 has always been considered to present considerable diffi- 

 culty ; and the theoretical suggestions which have been made 

 as to the measure of intensity have not been regarded as con- 

 clusive. The problem, however, is solved empirically every day; 

 and the comparison of the intensity of sounds not differing 

 widely in pitch presents no great difficulty. 



The tones of every keyed instrument are so proportioned in 

 power that in all parts of the range the effect may be as uniform 

 as possible ; and in the case of the organ, in which the power 

 of each pipe is fixed once for all by the voicer, we have in each 

 stop a graduated series of tones, the power of which has been 

 adjusted to the production of a uniform effect, by the exercise 

 of a skill more easy to admire than to imitate. 



Strictly speaking, the effort of an organ-voicer is to make the 

 more acute tones so far prominent above the lower ones, that 

 the higher may be clearly heard through the lower. That the 



