160 CHEMISTRY OF NATURAL WATERS. [IX. 



recent water was feebly alkaline to litmus, but did not affect 

 the color of curcuma-paper. 



These characters showed the recent water to contain a solu- 

 ble monosulphide, whose presence was further indicated by the 

 addition of a solution of green vitriol, which gave an abun- 

 dant precipitate of sulphide of iron. Kitroprusside of sodium 

 gave a fine purple color with the water, which was rendered 

 more intense by the previous addition of a little caustic soda. 



When boiled, the recent water evolves an abundance of sul- 

 phuretted hydrogen, and after twenty minutes of ebullition 

 the reaction of sulphur disappears from the water ; which be- 

 comes turbid, from the separation of a hydrate of magnesia, 

 readily soluble in a cold solution of sal-ammoniac. Crystals of 

 gypsum are also deposited during the boiling. This volatiliza- 

 tion of the sulphur is evidently due to the well-known de- 

 composition of sulphide of magnesium, by boiling, into hydrated 

 oxide of magnesium and sulphuretted hydrogen gas. It was, 

 however, a question whether the whole of the sulphur in the 

 recent water existed as a sulphide of sodium or magnesium, or 

 whether a portion was present as sulphide of hydrogen, giving 

 with the former a double sulphide MgS,HS. This problem, 

 of considerable delicacy, can only be solved by indirect means. 

 For the determination of the whole amount of sulphide in the 

 recent water, having at the well no other suitable reagent, I 

 added to two bottles of the water a few grammes each of sul- 

 phate of copper ; the sulphide thus precipitated was afterwards 

 collected and analyzed. In that from one bottle the amount 

 of sulphur in the precipitate was directly determined, wliile in 

 the other it was deduced from that of the copper. These two 

 results gave, respectively, .460 and .464 grammes of sulphur to 

 the litre of water, the mean of which, .462, is equal to .491 

 grammes of sulphide of hydrogen. In addition to these, a de- 

 termination was made with the water brought to the labora- 

 tory. This, when mingled with an acid solution of terchloride 

 of arsenic, gave a quantity of tersulphide of arsenic equal to 

 .460 grammes of sulphuretted hydrogen, indicating a slight 

 loss of sulphur. 



