M. Hittorf on Phosphorus. 311 



(that is, the heat which becomes free solely from combination) 

 can be determined ; and it is only chemical equivalents thus cor- 

 rected which are comparable one with another. In calculating 

 B, the author assumes that elements in their compounds assume 

 equal values. We have then 



B = 



-2, c+ V^ i . Cp 



2v.d 



2v.d l 



in which V, v, v^ are the atomic volumes, d and d v the coefficients 

 of expansion, and C and C x the specific heats of the elements. 

 In this way the following Table has been calculated : — 





v. 



Atomic Tolume. 



T. 



B. 



T-B. 



d and d^. 





Atomic 

 volume 

 of com- 

 pound. 



Of the 



metal, 



v. 



Of the 

 haloid, 



Favre and 

 Silber- 

 mann. 







Coefficient of 

 cubical expansion. 



KCl 

 AgCl 

 AgBr 

 Agl 



37-4 

 26 

 29-6 

 42-7 



45 4 

 10-35 

 10-35 

 10-35 



26-7 

 26-7 



26-7 

 25-5 



+100960 

 + 34800 

 -f 25618 

 + 18651 



+ 17183 



- 30651 



- 41861 

 -107757 



83777 



65451 



77479 



126408 



Ag = 0-00005973 

 Br =0001264 

 I =0000856 

 K =0-000243 



By comparing the coefficient of expansion of the metals with 

 their chemical nature, the author comes to the conclusion that 

 within certain groups of metals (Pb, Fe, Ag, and Sn or Zn, Cd, 

 Cu) the coefficient of expansion is inversely proportional to the 



number of atoms in the unit of volume, that is = -, or, what is 



the same thing, directly proportional to the cube of their dis- 

 tances, i. e. =r 3 . 



Hittorf has published* a series of experiments on phosphorus, 

 the principal results of which are as follows. In order to study 

 the circumstances under which red phosphorus passes into the 

 condition of ordinary phosphorus, purified red phosphorus was 

 hermetically sealed in glass tubes from which the air had been 

 completely exhausted, and then exposed to various temperatures. 

 This was effected by suspending such tubes in test-tubes in 

 which the vapours of various substances were formed, the tempe- 

 rature of which varied from 255° C. to 530° C. The substances, 

 with the corresponding temperature of their vapours, were ben- 

 zoic acid, 255° C; chloride of mercury, 307° C; bromide of 

 mercury, 324° C. ; iodide of mercury, 358° C; sulphur, 447° C. ; 

 and sulphide of phosphorus, 530° C. In some cases the arrange- 

 ment was so modified that the tubes could be heated in the 

 * Poggendorff's Annalen, October 1865. 



Y2 



