180 MR J. Y. BUCHANAN ON THE 



rise of temperature. On adding further fractions of salt this ceased, the thermal effect 

 was reversed, and when saturation had been effected the temperature of the solution 

 had fallen below the initial temperature of the water used. 



No experiments have been made on solutions of beryllium chloride of greater con- 

 centration than 1/2 gram-molecule per thousand grams of water. 



The preceding table contains all the experimental results and the deductions there- 

 from. The form and the symbols used have been already explained. 



§ 100. Before discussing the data of the tables, attention must be directed to the 

 distinctive characters of the three salts. While the bases BeO, MgO, and CaO give an 

 alkaline reaction with litmus paper, the chlorides of magnesium and of calcium are 

 neutral, while that of beryllium is acid. In order to obtain, if possible, a neutral 

 solution of BeClg, the method adopted was to proceed by way of the sulphate and 

 double decomposition with chloride of barium. A solution of pure crystallised sulphate 

 of beryllium, containing exactly 1 gram-molecule of BeSO^ in 1000 grams of water, 

 was made, and with it was mixed a quantity of a solution of barium chloride containing 

 exactly 1 gram-molecule of BaClg in 1000 grams of water. The barium sulphate was 

 precipitated completely, and the supernatant liquid contained exactly 1 gram-molecule 

 of BeClg in 2000 grams of water, or, at the rate of 1/2 BeCla in 1000 grams of water. 

 This solution, which still had an acid reaction, was used for the preparation of the less 

 concentrated ones by exact dilution. It is impossible to produce solutions in this 

 way for which m>l/2, on account of the bulk of the barium sulphate produced. 

 Solutions of the highest attainable degree of concentration were prepared in the case of 

 magnesium chloride and calcium chloride, the concentration being determined by the 

 usual chemical methods, and the solutions of a lesser degree of concentration were 

 prepared from these. 



In all cases the solutions were prepared by diluting the more concentrated solution 

 immediately preceding it, a method capable of a high degree of precision, which is 

 shown by the fact that, after the experiments on strong solutions of MgCl.2 were com- 

 pleted, a single determination of the concentration of the 1 gram-molecule solution of 

 MgClz gave a result of 0'9991 gram-molecule of salt in 1000 grams of water. The 

 result was obtained by a determination of the chlorine content. 



Chlorine found ....... 662 per cent. 



,, calculated ...... 6"63 „ 



Diff. 0-01 



The specific gravity experiments were carried out by the use of the open hydro- 

 meters A and B in the case of strong solutions of the salts, magnesium chloride and 

 calcium chloride ; and by the use of the closed hydrometers Nos. 3 and 17 in the case 

 of the solutions of each of the three salts where the concentrations were less than I'O 

 gram-molecule of salt in 1000 grams of water. 



The constant experimental temperature was 19 "50° C. 



