M. E. Wiedemann on the Specific Heats of Gases. 85 



of a caoutchouc stopper. Two glass tubes, a wider (yjr) and a 

 narrower (g), pass through this stopper. A balloon of thick 

 black caoutchouc, Q, holding about 20 litres of gas, is con- 

 nected with the wider tube ^, which is closed by means of a 

 caoutchouc stopper carrying two tubes — i leading to the heat- 

 ing-apparatus, and the other, leading to the manometer, k. 

 The manometer consists of a glass, r, into which the graduated 

 tube k is fastened air-tight. By means of the stopcock h } 

 communication can be made or broken between Q and the 

 manometer. Very wide stopcocks, T and V, are placed on 

 the tubes g and i. 



The second balloon, B, besides communicating with Q, is 

 fitted with two holes — one leading to the manometer, e, the 

 other passing to the bottom of the vessel, and capable of being- 

 brought into connexion by means of the stopcock S with the 

 water-cistern A. The tubes establishing communication be- 

 tween B and C are so wide that the pressure in each will not 

 alter during the escape of gas from Q. 



The manometers e and k contain water ; the smallest varia- 

 tions in pressure can therefore be easily read off without the 

 use of a cathetometer. Inasmuch as communication between 

 Q and r is made by means of a tube 40 centims. in length and 

 bent many times, and also inasmuch as each experiment only 

 lasts for a short time, the wetting of the gas in the balloon Q 

 is not to be feared. 



B stands upon a bridge-balance, by means of which the 

 weight of this balloon can be ascertained to within 5 grins, 

 with certainty. The gas escaping from Q is sent through an 

 apparatus F, consisting of two tubes so connected together 

 that the gas passes through the inner, then gives up its heat 

 to a thermometer, and finally passes on through the outer 

 tube. These tubes are placed in a wooden case. The tem- 

 perature possessed by the gas issuing from Q is thus ascer- 

 tained. By causing the gas to bubble through a cylinder 

 filled with sulphuric acid or with mercury, #, the rate at which 

 it is flowing is noticed. The apparatus y is filled with little 

 glass beads, and serves to retain any sulphuric acid which 

 may have been mechanically carried over from x. 



Before carrying out determinations of the specific heats of 

 gases with the apparatus just described, it was necessary to 

 ascertain with certainty whether or not the temperature of the 

 gas as it issued from the heating-vessel was really the same 

 as that of the liquid in the vessel. For this purpose an ap- 

 paratus similar to that employed for determining the tempe- 

 rature of the gas before it entered the heating-vessel was 

 placed in connexion with the German-silver tube leading 



