C. ELECTRICITY, LIGHT, HEAT, AND SOUND. 49 



The gauze should be held steadily about two inches above 

 the burner, by means of a retort-stand. The flame is a slen- 

 der cone about four inches high, the upper portion giving a 

 bright yellow light, the base being a non-luminous blue flame. 

 At the least noise this flame roars, sinking down to the sur- 

 face of the gauze, becoming at the same time almost invis- 

 ible. It is very active in its responses, and being rather a 

 noisy flame, its sympathy is apparent to the ear as well as to 

 the eye. 



To the vowel sounds it does not seem to answer so dis- 

 criminately as the vowel flame of Professor Tyndall. It is 

 extremely sensitive to , very slightly to e, more so to i, en- 

 tirely insensitive to 0, but slightly sensitive to u. It dances 

 in the most perfect manner to a small musical snuff-box, and 

 is highly sensitive to most of the sonorous vibrations which 

 affect the vowel flame, though it possesses some points of dif- 

 ference. 12 A, November 9,1871,30. 



HEAT OP COMBUSTION OF STONE-COAL. 



In a careful inquiry upon the heat of combustion of stone- 

 coal by Scheurer-Kestner and Meunier, the conclusion was 

 reached that during the formation of coal a certain quantity 

 of heat must have been absorbed, since the theoretical heat 

 of combustion was always less than that actually observed. 

 In our entire ignorance of the constitution of coal, it is im- 

 possible, however, according to the authors, to determine the 

 nature of this absorption. It would furthermore appear that, 

 from our want of knowledge of the composition of coal, we 

 can not calculate the heat of combustion. Two coals of pre- 

 cisely the same chemical composition may and do afford very 

 different degrees of heat in combustion. 18 C, xxxiii., Aug- 

 ust 16,1871,523. 



ON HEAT EVOLVED IN THE FORMATION OF AQUEOUS SOLU- 

 TIONS. 



In a memoir by Mohr upon the heat evolved in the forma- 

 tion of aqueous solutions, it is stated that the fall of temper- 

 ature occasioned by the solution of salt in water, or by mix- 

 ing salt with snow, is to be ascribed to a change in the state 

 of aggregation. Referring, however, to the fact that a fall 

 of temperature is observed when an aqueous solution of com- 



C 



