114 Mr. J. P. Joule on the Theoretical Velocity of Sound. 



No. 5. This watei'' was from a retting pit in Holland. 



100,000 grains, evaporated to dryness, gave a residue of 



42*4< grains, which consisted, per cent., of — 



Protoxide of iron . . . . 1*183 



Lime ... . . . . . 3-613 



Magnesia 7-601 



Soda 19-277 



Potash 8-205 



Sulphuric acid 5*607 



Muriatic acid ..... 9*439 



Carbonic acid, with organic! a ^ r^^r- 

 a\ f 45-075 



matter and loss. . . J 



100-000 

 With regard to the constitution of these several specimens 

 of water, it can only now be remarked, that in all there was 

 present a large quantity of mineral impurities ; and that in 

 Nos. 2 and 4, the very samples which are of the most remark- 

 able and celebrated steeping waters in Belgium, a large quan- 

 tity of iron is present, so that they might be in a degree termed 

 chalybeate waters. How this regards their excellence for 

 preparing flax 1 do not pretend to say, and indeed it will 

 require much more extended investigation before a satisfactory 

 solution of it can be given. 



All these waters are further remarkable for containing a 

 larger quantity of potash than ordinary waters are found usu- 

 ally to have. I shall not, however, enter minutely into the 

 discussion of their constitution, as I shall have to resume the 

 subject at another time; and I wish only to place on record 

 for the present the analytical results which the samples of 

 waters forwarded to me from Belgium by Mr. Marshall, had 

 afforded. 



XXI. On the Theoretical Velocity of Sound. By J. P. Joule *. 



THE celebrated French mathematician De Laplace has, 

 it is well known, pointed out that the heat evolved by 

 the compression of air is the cause of the velocity of sound, 

 according to the theory of Newton, being so much less than 

 that actually observed. He has also given a formula by which 

 the velocity may be determined when the ratio of the specific 

 heat of air at constant pressure to that at constant volume is 

 known. The determination of the elevation of temperature in 

 air by compression has however been hitherto attended with 

 difficulty, and hence the theorem of De Laplace has never yet 

 been fairly compared with experiment. I was therefore anxious 

 * Communicated by the Author. 



