Mr. W. J. M. Rankine on Laplace^s Theory of Sound. 225 



more probable, as apiine having its full amount of hygrometric 

 moisture, namely 4"2 per cent., and having this water saturated 

 M'ith hydrochloric acid. This latter ^dew accounts for the in- 

 crease of weight in a veiy satisfactory manner ; the hygrometric 

 moistui'e might be easily derived from the not absolutely anhy- 

 drous gas. Again, this substance cannot exist in contact Avith 

 water, even in the cold ; so that, on the whole, although the 

 formula C^^ H^^ 0^^ is probably as good as any other, yet these 

 experiments do not warrant this conclusion, and it is preferable 

 to employ the more simple one, C^* H^"* O^^, at first fixed upon. 



IX. Reactions. 



It only remains now to give the reactions of apiine with the 

 various reagents. These are few in number; indeed there is 

 only one which is highly characteristic, viz. that with a salt of 

 iron. 



^^Tien a solution of apiine in water or in alcohol is mixed with 

 a neutral solution of sulphate of iron, it becomes of a deep 

 brownish-red coloiu*; and this reaction is so delicate, that 1 grm. 

 of apiine dissolved in 10 litres of water, or 1 part in 10,000, can 

 be detected. The same efi'ect is produced with perchloride of 

 iron, provided the solution is not strongly acid. Apiine is also 

 a test for iron ; 1 drop of solution of perchloride in a test-tube 

 full of water is easily detected. Filtering paper, containing not 

 more than two or three-tenths per cent, of ash, which is scarcely 

 coloured by the iron it contains, becomes of a light reddish- 

 browai tint when a hot solution of apiine is passed through it. 



Apiine gives no precipitate mth solutions of chloride of barium, 

 acetate of lead, nitrate of silver and ammonio-nitrate of silver. 

 A flocculent yellow precipitate occurs with solution of basic ace- 

 tate of lead. Solution of chloride of barium, to which ammonia 

 has been added, also gives a yellow precipitate. 



Andersonian Universitj' Laboratory, 

 Glasgow, 19th Dec. 1850. 



XXX. On Laplace's Theory of Sound. By AVilliam John 

 Macquorn Rankine, C.E., F.R.S.E., F.R.S.S.A. ^r.* 



WITHOUT for the present attempting to criticise Professor 

 Potter's theory of the jn-opagation of sound in air (Phi- 

 losophical Magazine, February IH.'jI), I beg leave to offer a few 

 remarks on a passage in which it appears to me that he has (of 

 course unintentionally) done injustice to Laplace, and to those 

 who have adopted the views of that mathematician. 

 The passage to which I refer is the following : — 



" Laplace .... maintained that the sensible heat 



* Communicated by the Author. 

 Phil. Mag. S. 4. Vol. 1. No. 3. March 1851. Q 



