Chemistry and Physics. 325 



crystallized variety by treating it several times with hydrochloric 

 acid, washing and drying it, and heating it to redness in the open 

 air for a short time. The diamonds used were those known as 

 Cape diamonds aud contained 0*12 per cent of ash ; though 

 essentially the same results were obtained with bort. The char- 

 coal was burned with oxygen in a calorimetrical bomb under a 

 pressure of 25 atmospheres. The graphite was mixed with from 

 one-third to one-fifth its weight of naphthalene, the heat of 

 combustion of which is accurately known, in order to burn it in 

 the bomb. The diamonds finely pulverized were mixed with 11 

 to 16 per cent of naphthalene. Six determinations were made 

 with charcoal, five with graphite, four with Cape diamonds and 

 two with bort. The heat of combustion of one gram was found 

 to be for charcoal 8137*4 water-gram-degrees, for graphite 7901*2 

 water-gram-degrees and for diamonds 7859-0 water-gram-degrees. 

 Thus 



C (diamond) + 2 = C0 2 develops +94-31 cal. 

 C (graphite) +O s =C0 9 " +94-81" 

 C (charcoal) +O a = CO, " +97-63" 

 — C. H., cviii, 1144-1148. G. f. b. 



2. On the Molecular Mass of Dissolved Substances. — Will and 

 Bredig have devised a modification of the methods of Tamman 

 and Walker for estimating the vapor-pressure of a solution in 

 order to measure the influence of the substance in solution on the 

 vapor-pressure of the solvent, and so, from the results obtained, 

 to determine the molecular mass of the dissolved substance. The 

 solution is contained in a specially constructed Liebig apparatus 

 having a number of bulbs, and the pure solvent itself is contained 

 in a second and similar bulb. These two bulbs are weighed, 

 joined in series, and air is passed through them for twenty four 

 hours at the rate of about a liter per hour, both bulbs being im- 

 mersed in a bath of constant temperature. At the end of the 

 operation the bulbs are again weighed. The loss in weight of 

 the first is proportional to the vapor-pressure of the solution, that 

 of the second to the difference of the vapor-pressures of the pure 

 solvent and of the solution. From these figures the molecular 

 mass of the dissolved substance may be calculated by Raoult's 



formula M = m . — . / „ ., 



100 /-/" 



in which M is the molecular mass of the dissolved substance, m 



is the molecular mass of the solvent (for alcohol 46), p is the 



number of grams of substance dissolved in 100 grams of the 



solvent,/" is the vapor-pressure of the solvent and/'' that of the 



solution both at the same temperature. If s be the loss in weight 



of the bulbs containing the solution, and s" that of the bulbs 



f s' 



containing the solvent, then -^- — -, = —rr and the above formula 



becomes M = m . - — . — r .. 



100 s" 



