ATMOSPHERIC PRESSURE BETWEEN 104 C. AND 115 C. 409 



the inner surface of the cork. A water manometer, Q, was also attached to the 

 brass tube so that an approximate estimate of the pressure in the space surrounding 

 the calorimeter could be made. 



The, Heating Coil. 



This consisted of about 130 cm. of '004-inch platinum wire, bent double, the 

 two strands being wound, in parallel, on a serrated mica frame. The loop end was 

 gold-soldered to a piece of 0'008-inch platinum wire which was fixed centrally along 

 the mica framework. A length of 12 cm. of No. 22 silver wire, bent double, was 

 joined at its loop to the free end of this thicker platinum wire, and the two other 

 free ends of the 0'004-inch platinum wire were likewise soldered to the loop end of 

 a similar piece of silver wire. These silver wires were bound to the mica frame, 

 which was always immersed to a depth of 4 or 5 cm. in that part of the current 

 of steam which was actually heated ; thus any error due to conduction of heat from 

 the heating coil was prevented. The four free ends of these silver wires were then 

 soldered to the main current and potential leads. Each of these leads was a length 

 of No. 20 copper wire, to the upper end of which was hard soldered about 1 cm. of 

 No. 27 platinum wire. A thin lead glass tube enclosed each conductor and was fused 

 round the platinum wire. The leads thus enclosed were brought down symmetrically 

 around the glass jacket, S, surrounding the flow-tube, Y, and were carried by the 

 split cork. The general arrangement is indicated in figs. 7 and 8, P P being the 

 potential and 1 1 the current leads. 



The Thermometer. 



This consisted of about 120 cm. of 0'004 inch platinum wire, wound in a screw 

 thread of 40 turns per cm., cut on an ivory cylinder. This was carried on a long 

 lead of No. 24 copper wire, the latter passing axially through to the far end of 

 the cylinder. The cylinder was fixed in its position on the wire between two 

 small lumps of solder. The ends of the platinum wire were soldered, one to the 

 lower end of this lead, the other to the end of a length of No. 28 copper wire 

 which only reached as far as the near end of the ivory cylinder. Another pair of 

 leads, consisting of equal lengths of Nos. 24 and 28 copper wire, which again 

 only reached as far as the near end of the cylinder, where their ends were 

 soldered, formed the compensating leads of the thermometer. All these leads 

 were enclosed in fine glass capillary tubes firmly bound together with silk. Before 

 winding the platinum wire, the ivory was baked for some time at a temperature 

 of about 120 C. in order to shrink the cylinder. The over-all length of the 

 thermometer was 35 cm., the platinum wire being wound over a length of 

 3'6 cm. of ivory. The thermometer and leads were enclosed in a glass sheath, N 

 (fig. 7), 2 '5 mm. in diameter, which was carried by a rubber cork fixed tightly 



3 I 2 



