T II E 

 LONDON, EDINBURGH and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[THIRD SERIES.] 



JANUARY 1842. 



I. Abstract of Thermometrical Researches. £ij/ Professor Hess 

 of St. Petersburgli^ . 

 [Continued from vol. xix. p. 183, and concluded.] 

 IVT HESS having determined, as already described, the 

 ^^* quantitiesof heat evolved by the combination of muriatic 

 acid with potash, soda, and ammonia, proceeded to examine 

 its relations to lime. The quantity of heat evolved by the 

 combination of the acid H CI + 12 Aq with slaked lime, he 

 found to be represented in four experiments with the calori- 

 meter by the numbers 435*2, 437"6, 436*3, 449'6, in mean re- 

 sult 439'7 units of heat for an atom of the acid. In order to 

 control this number he made a series of experiments with un- 

 slaked lime, which were found, however, very difficult of 

 accurate performance, as the lime became hard, and did not 

 at all easily or rapidly combine with the acid. The numbers 

 which he obtained were 580-7, 606-1, and 612. In deter- 

 mining previously the quantity of heat evolved by lime in 

 slaking, he had deduced the number 167"2, but he repeated 

 the experiment twice, and found 161*4 and 160-5, the mean 

 of the three numbers being 163-03. Subtracting this from 

 the mean of the numbers obtained with unslaked lime (599-6), 

 the remainder, 436*57, fully confirms the number 439*7 ob- 

 tained as the mean result of the trials with slaked lime. 



M. Hess found that dry chloride of calcium gives out, when 

 dissolving in water, 236*4 units of heat : this, however, is not all 

 due to the fixation of the six atoms of water of crystallization, 

 as the hydrated salt Ca CI + 6 Aq, when dissolved, gave out 

 33*65 units of heat. 



• Krom PoggendorH's Annakn, vol. Hi. p. !)7- 

 Phil. Mas. S. 3. Vol. 20. No. 128. Jan. 1842. B 



