168 Prof. E. Bunsen on the Condensation of 



only a few tenths of a degree during a whole day. The obser- 

 vations on the apparatus filled with carbonic acid were com- 

 menced on the 20th of April, 1880. By the 8th of August of 

 the same year the condensation of gas had so far advanced 

 that the 600 millimetres of the measuring-tube threatened to 

 be insufficient for further readings. To allow of a continuance 

 of the readings it was necessary to add fresh carbonic acid to 

 that still present. This may be carried out without interrupting 

 the series of observations already commenced in the following 

 way : — After the volume of gas v x condensed on the threads 

 in the time T has been estimated, the stopcock b (fig. 1) 

 is closed. In the closed vessel A, the known pressure P 

 and temperature t a , at which the estimation of Vi was made, 

 still holds. Let, then, the requisite volume of dry gas be added 

 to that already present by passing it directly into the mea- 

 suring-tube dipping under mercury, and, after the equilibrium 

 of temperature and pressure has been established, let the 

 volume of carbonic-acid gas Y m now present in the measuring- 

 tube and its pressure P m and temperature t m be noted. 



From these observed values, which were as follows, a new 

 constant A 1 can be obtained by means of equation (5) : — 



V a =112-397 cub. cent,, t a =18°'2 C, P a =0-3091; 



Y h = 0-0478 „ t h =18°-2 C, P A = 0'3091 ; 



Y m = 83-265 „ * m =17°-3C., P m =0-7278. 



Vl = 33-009; A 1 = 117-863. 



The observations taken after the 8th of August, 1880, were 

 calculated according to the equation 



„ s =117-863- , 76(1 + l mm) (il*4AS + Yj 



This gives the volume in cubic centimetres of carbonic acid at 

 0° C. and 0*76 metre pressure, which was condensed from the 

 time of closing the stopcock b when the additional volume of 

 carbonic acid was passed in. If we add now to the constant 

 117*863 the volume ^ = 33-009 of carbonic acid already con- 

 densed up to the time of closing the stopcock, the equation 

 then gives the volume v which has been condensed from the 

 commencement of the experiments. 



In Table IV. are summed up the results attained with dry 

 carbonic acid. The first numbers are the means of many ob- 

 servations taken hourly, then daily ; the numbers represented 



