246 



HYDROGENATKD COMPOUNDS OF NITROGEN. 



(3) The small tube is wound round with a thick and heavy 

 spiral of platinum, gg, intended later on to plunge the system 

 below the level of the potash, and thus to determine the contact 

 and the reaction between the alkaline solution and the solid salt. 



(4) The upper end of this spiral is hooked on to a platinum 

 wire 2^ mm*, in diameter, stretched between the two copper 

 wires of a small electric cable of gutta-percha, KK. This 

 cable is intended to convey the current, which is to heat to 

 redness and finally melt the little platinum wire, allowing the 

 small tube to fall into the solution of potash, where the salt 

 will react after its submersion. 



(5) The large glass tube, TT, is closed with a cork, through 

 which on one side passes the cable which winds in and out 

 until outside the apparatus, and through the other side is passed 

 a tube, dd, used for the liberation of gases. 



(6) This large glass tube, TT^ and the tube dd, including the 



curved extremity of this latter, 

 through which the gases are to 

 escape, are contained together 

 in a small bell glass rather wide 

 and capable of containing 200 to 

 250 cms. of gas, a volume con- 

 siderably larger than that of the 

 gases given off in the reaction. 



(7) This bell glass is in its 

 turn placed upside down with 

 its tubes and appurtenances, 

 in an ordinary platinum calori- 

 meter, CC, of a capacity of 

 1050 cms., but containing only 

 850 grms. of distilled water. 



Thick copper wires, uu, ar- 



Fig. 42. 



ranged beforehand in the form- of a star round a central point 

 on the upper surface and on the axis of the bell glass, support 

 it and keep it in a fixed position under the water. These 

 wires are connected with a centra! rod, S, which rises verti- 

 cally above the apparatus, and enables it to be attended to 

 without any special instrument being introduced into the 

 calorimeter. " 



It need not be said that the weight of .each portion of this 

 complicated apparatus was determined beforehand, so as to 

 enable us to reduce the submerged masses to units of water. 

 Moreover, special measurements of the specific heat of the cable 

 and that of the cork were taken ; these measurements may be 

 made somewhat roughly, since the weight of the cable sub- 

 merged does not exceed a few grammes ; that of the cork is 

 still less. As to the' glass, copper, and platinum, their specific 

 heat is known. 



