422 (iUKJKSILVER DEPOSITS OF THE PACIFIC SLOPE. 



soluble in barium sulphide and Professor Roth' thinks it i)robable that cal- 

 cium sulphide possesses a similar power. 



Solubility of Hgs in mixtures of Na^s and NaOH. — A series of experlnieuts was made 

 in my laboratory with a view of testing the relative effect of the quantity 

 of sodium sulphide and sodium hydrate on the quantity of mercuric sulphide 

 which a given mixture of the solvents would take up. It is almost impos- 

 sible to make experiments of this kind with tlie same accurac}- which can 

 easily be attained in precipitations, because, if one or more drops of either 

 fluid reagent be added to a mass consisting of mercuric sulphide partially 

 dissolved in the menstruum, it is not practicable to say how long a time will 

 elapse before the additional drop will have become saturated. Approximate 

 results are, however, readily obtained, and these appear in the present case 

 to be sufficient. 



It was found that, provided a small quantity of free hydrate exists in 

 the mixture, the solubility of mercuric sulphide depends upon the quantity 

 of sodium sulphide in the solution, or, in other words, that, if to a mixture of 

 Na^S and NaOH more sodic hydrate be added, the solvent power of the mixt- 

 ure is neither increased nor diminished thereby. For example, three solu- 

 tions, containing, respectively, 0.95, 1.38, and 2.29 grams of sodic hydrate, 

 and each containing almost the same quantity of sodic sulphide (about 0.7 

 gram), each dissolved the same quantity of mercuric sulphide. A very 

 small quantity only of the hydrate is sufficient to secure to the alkaline 

 sulphide its maximum solvent power over mercuric sulphide. The greater 

 part of the experiments made to test the maximum solubility of IlgS in 

 Na^S in the presence of NaHO shows that the relation of the weights of 

 the two substances is very nearly in the proportion of one molecule of HgS 

 to two molecules of Na'S. The average of fourteen such experiments gives 

 iHgS to 2.03Na^S. From the nature of the experiments a slight excess in 

 the quantity of the solvents employed is to be expected. One experiment 

 was made by mixing mercuric and sodic sulphide in the proportion of two 

 molecules of the latter to one of the former and adding a few drops of caus- 

 tic soda. A mere trace of the metallic sulphide remained undissolved and 



I Alls- und cbeni. Geol., vol. 1, l«7;t, p. 2GJ. 



