Intelligence and Miscellaneous Articles. 391 



vapours. It is simply necessary to melt sodium in the open air in a 

 flat iron dish over a small gas-flame, and, the spectrum apparatus 

 being placed on a somewhat inclined plane, the slit of the telescope 

 is directed obliquely on the ignited metallic surface. If the metal 

 becomes covered with a coating, it is heated by a Bunsen's flame 

 directed downwards upon it. The surface is thus kept clean. 



If the flame under the dish is very small, a continuous spectrum 

 only is seen. With stronger heating, white vapours are disengaged 

 and the black lines occur. Tf the flame is allowed to surround the 

 small dish, the line is observed to be yellow. It is easy also to 

 regulate the flame so that the line is black with yellow edges. — 

 Zeitschrift fur Chemie, vol. i. part 15. 



NOTE ON THE VELOCITY OF SOUND, AND ON THE MECHANICAL 

 ENERGY OF CHEMICAL ACTIONS. BY DR. SCHRODER VAN DER 

 KOLK. 



Dear Sir, Zutphen, August 17, 1865. 



I see from the July Number of the Philosophical Magazine that 

 you have done me the honour to translate into English my paper 

 on the Velocity of Sound, for which I beg to thank you. Since, 

 however, a few misprints occur in the German version, in the 

 formula? as well as in the text, page 3, I take the liberty of sending 

 you a corrected copy. In the case of the three mistakes which you 

 have yourself noticed, you are perfectly right : they were clerical 

 errors in the manuscript, but fortunately they do not affect the result. 

 I sent the calculation of the Mechanical Equivalent to Poggendorff as 

 early as February, but it has not yet appeared. The value found is 

 422*10, which agrees pretty well with Joule's number. 



I am also greatly indebted to you for your remarks upon my paper 

 " On the Mechanical Energy of Chemical Actions." Your remarks 

 on page 273 in regard to phosphorus, and on page 276 about the 

 oxide of copper, are correct. With regard to oil of turpentine, I 

 must, however, observe that I did not by any means assert that it 

 remains unaltered ; but, as I had read somewhere or other that such 

 was the case, I was wishful to anticipate the objection that in this 

 instance a body passed of itself into a higher state of energy, and 

 left it an open question whether it was so or not. If it is altered, 

 so much the better. On page 278 you ask why should silver impart 

 more heat to the water than porcelain would do ? I never said that 

 it would ; porcelain, however, would not fulfil the second condition, 

 namely, acting differently on the constituents of the water. On the 

 other hand, a body must satisfy both conditions in order to decom- 

 pose the water. Your remark on page 280 is quite correct ; I ought 

 to have added that I here used the expressions stronger and weaker 

 base, as well as greater and less affinity, in the sense which they 

 bear in common language ; for in what follows I point out the inad- 

 missible character of these distinctions, as well as the difficulty there 

 is in giving a correct definition of them. 



