258 Dr. C. R. A. Wright on the Determination of 



value of a " mean calory ") is 1*005. On the other hand, 

 Bosscha has revised the data on which Regnault founded his 

 formula (Pogg. Ann. Jubelbd. p. 549), and gives the two 

 following expressions for the quantities Q and S: — 



q=* +o*ooom 2 , 



S = l + 0-00022*; 



whence the mean specific heat between 0° and 100° is 1*011, 

 a value largely exceeding Regnault's. Employing Regnault's 

 value, the heat-evolution observed by Schuller and Wartha 

 becomes 34126*1 x 1*005 = 34,297 gramme-degrees ; whilst if 

 Bosscha's formula be employed (as was done by Schuller 

 and Wartha in comparing their results with those of other 

 observers), the heat evolution becomes 34126*1x1*011 = 

 34,501 gramme-degrees. 



26. Shortly before these experiments were published, von 

 Than found, by nearly the same mode of operating, that 1 

 gramme of hydrogen and 7*98 of oxygen, at 0° and 760 

 millims., liberate, in forming water, 33,928 gramme-degrees 

 (Deut. diem. Ges. Ber. 1877, vol. x. p. 947). The chief dif- 

 ference between his experiments and those of Schuller and 

 Wartha was that, whilst the latter weighed the mercury 

 sucked into the calorimeter through the melting of the ice, 

 von Than measured it in a capillary tube according to Bun- 

 sen's plan, using Bunsen's value for a gramme-degree as above 

 defined in terms of mercury sucked in. Schuller and Wartha 

 calculate, from Bunsen's data, that the quantity of mercury 

 corresponding to a " mean calory " is 0*01541 gramme, 

 whilst their own determinations give 0*015442; von Than 

 used values corresponding to the former number, whilst 

 Schuller and Wartha employed the latter. The differences 

 between each of the values used and the true value are 

 included in the experimental errors of determination in 

 the two heat- evolutions — viz. 34,297 (Regnault) or 34,501 

 (Bosscha), found by Schuller and Wartha, and 33,928 ob- 

 served by von Than. 



27. A few years previously Julius Thomsen found (Pogg. 

 Ann. 1873, vol. cxlviii. p. 368), from three accordant obser- 

 vations, that the formation of 17*96 grammes of water from 

 dry oxygen and hydrogen, all materials and products being 

 at near to 18°, produces an evolution of heat sufficient to raise 

 the temperature of 68,207 grammes of water 1°, the water 

 being to start with at close to 18°; the heat required to raise 

 the temperature of the water produced being allowed for in 

 the determination. From Regnault's formula (§ 25) the 

 specific heat of water at 18° is 1*00101, and from Bosscha's 



