506 MM. Bunsen and SchischkoflF^s Chemical 



to 

 flame has indeed a constant temperature - throughout the du- 

 ration of the experiment, but this temperature only extends to 

 the infinitely small layer which is in the act of exploding, and 

 from radiation and conduction diminishes in a fixed ratio from 

 this layer to the point of the flame. 



If therefore we wish to know the temperature of the flame as 

 produced by the process of combustion, and not afiiected by 

 foreign influences, we must calculate it from the values w and s. 



As w, the heat of combustion of powder, was unknown, we 

 determined it in the following manner : — A, fig. 4, is a brass 

 tube filled with a compressed mass of finely pulverized gun- 

 powder of known weight p. In the wider part of this tube a 

 glass piece b is cemented, in which the platinum wires cc are 

 fused. These wires are in connexion with a fine capillary pla- 

 tinum wire dipping in the powder. This small apparatus. A, is 

 placed in the glass tube B, which is closed at one end, and this, 

 together with the apparatus contained in it, is placed at the 

 bottom of the tube C. This is closed at the bottom, but still 

 open at the top, and is provided with two fine apertures at d d. 

 The two wires cc are passed through the apertures dd and 

 sealed at the blowpipe, and then the upper end of the tube c is 

 also hermetically closed. The tube C has a small projection at 

 its lower extremity, by which it is fitted in the cork K. By 

 means of this cork the whole arrangement is fixed in the wide 

 tube D, only half of which is seen in the figure. This consists 

 of the finest sheet brass, and contains a sieve-shaped stirring 

 arrangement, which can be moved up and down from without 

 by the fine wires ^^. The apparatus, the glass, platinum, and 

 brass parts of which have all been severally weighed, is filled 

 over the top with a weighed quantity of water, and, enclosed in 

 a wooden box, is left in a place inaccessible to change of tem- 

 perature until it has attained a uniform temperature. 



To determine with this apparatus the heat of combustion of 

 powder, the following time and temperature observations are 

 needed, the latter of which may be directly made on the ther- 

 mometer K, which is graduated to the j^,jth of a degree Centi- 

 grade, and is placed in the lateral enlargement of the brass 

 water-vessel. 



The temperature is first observed for the times / and ^, ; the 

 powder is then exploded by passing a galvanic current through 

 the wires cc, noting the time t^ — t^ which transpired from the 

 last observation to the commeneement of the explosion. The 

 time t^—t^ is then observed which elapses until the maximum 

 of the lieating from the explosion is reached. Finally, the times 

 ^4 and /g, counted from the maximum, and their corresponding 



