148 CALORIMETRIC APPARATUS. 



horizontal rings, B B', which hold the frame together at its ends, 

 and of four strong vertical rods, the whole being in platinum or 

 brass, as may be required. 



The blades, about O'OIO metre in width, and the rings of equal 

 breadth, are arranged so as to form a frame, concentric to an 

 internal cylindrical space, the whole being in its turn enveloped 

 and almost touched by the cylindrical vessel, V V, which con- 

 stitutes the calorimeter. 



Two of the vertical rods are prolonged about 0'15 metre above 

 the calorimeter, and joined at their upper end by a half ring of 

 wood, C C, of suitable width and thickness. The lower ring is 

 provided with four small feet or prolongations, a few millimetres 

 in length, and arranged so that the stirrer rests on their rounded 

 ends, at the bottom of the calorimeter. 



The whole may be seen, in the centre of the calorimeter 

 (Fig. 20). In the cylindrical space surrounded by the stirrer 

 are placed the thermometer and suitable apparatus. 



In order to employ this stirrer, the half ring is held in the 

 hand, or by some mechanical appliance (turn-spit, hydraulic, or 

 electro-magnetic motor, etc.), the stirrer is lifted a few millimetres, 

 and a horizontal and rotary movement around its vertical axis 

 is imparted to it. This movement is alternating, and comprises 

 an arc of from 30 to 35. In consequence the water in the 

 calorimeter is impelled towards the centre, and at all heights at 

 the same time, being sharply thrust forward by the heficoidal 

 blades, which strike the water at an angle of 45 with the 

 vertical. 



The degree of perfection which is hereby attained in the 

 mixture of the layers, and the promptitude with which this 

 result is obtained, even with a slight effort and slow movement, 

 are surprising. 



Besides, the stirrer not coming continually out of the liquid, 

 as happens with stirrers moved up and down, is not exposed to 

 the very sensible evaporation to which the latter give rise, nor 

 to the causes of error which result therefrom. 



4. The calorimeter just described may be employed under 

 extremely varied conditions. A full account will be found in 

 the "Essai de Me'canique Chimique" and in the author's 

 "Memoires." Some of the special instruments employed for 

 effecting chemical reactions in the interior of this calorimeter 

 will be described in the following chapters, in connection with 

 the experiments for which they have been constructed. 



3. DETONATOR OR CALORIMETRIC BOMB. 



1. A description will now be given of the apparatus used to 

 measure by detonation both the heat of combustion of hydro- 

 carbon gases, or by an inverse process the heat of formation of 



