of Substances in the Liquid and Solid Condition. 515 



it was found possible to determine its heat of dissolution both 

 in the solid and liquid condition at the same temperature, 

 and from these the heat of fusion may be deduced. The sub- 

 stance in these determinations was enclosed in a glass bulb, 

 which was broken under the surface of the water. The 

 results, as will be seen, are not very concordant. This may 

 be due to the fact that the samples used were different pre- 

 parations, and may have been of different degrees of purity. 

 The same preparation, however, was used in the first-quoted 

 determination with the solid and in the first with the liquid, 

 and similarly with the two second determinations, and these 

 two pairs are concordant in the values which they give for 

 the heat of fusion, 10,230 cal. according to the first deter- 

 minations, 10,176 cal. according to the second. 



The anhydrous tetrabromide used was not satisfactorily 

 pure. The commercial sample obtained was found, in spite 

 of special care having been taken in its preparation, to con- 

 tain a considerable amount of dibromide, for, on melting it, 

 globules of the latter separated. After twelve fractionations 

 by crystallizing, a sample was obtained with 8 per cent, of 

 the dibromide, but further fractionation did not appear to 

 reduce the amount of this impurity : indeed the formation of 

 the dibromide seems to occur spontaneously in the tetra- 

 bromide, for it was often noticed that a specimen which was 

 perfectly clear and free from any visible globules of the 

 dibromide, would, on being melted again, leave particles of the 

 latter adhering to the glass ; yet in no case was the presence 

 of bromine indicated either by colour or smell. When water 

 is added to the tetrabromide, visible traces of bromine are 

 liberated. 



The values obtained for the heat of dissolution of the 

 anhydrous salt are not very concordant, but this may be 

 due to the different proportions of water used in the two 

 determinations. 



Hemiheptahydrate of Sodium Hydroxide (NaOH,3JH 2 0). — 

 The heat of formation of this hydrate (for a description of which 

 see Trans. Chem. Soc. 1893, p. 893) from the monohydrate and 

 water was determined. This does not constitute an unexcepr 

 tionable instance ; for one of the constituents itself being a 

 hydrate, and not a simple compound, the results are com' 

 plicated by the fact that the heat of fusion of this constituent 

 may not represent its true heat of fusion, but may include 

 some heat absorption due to partial dissociation on melting. 



In dealing with the monohydrate it was found that after 

 it had solidified in the platinum bottle containing the ther- 

 mometer, it was necessary to heat it very slowly indeed to 

 remelt it, so as to avoid breaking the bulb of the thermometer 



