334 SULPHUR. 



Preparation. If a mixture be made over mercury of 2 volumes 

 of sulphurous acid, and 4 volumes of nitric oxide, which are 

 combining measures of these gases, no change occurs ; but on 

 throwing up a strong solution of caustic potash into the gases., 

 they disappear entirely after some hours, combining with a 

 single equivalent of potash, and forming together the nitrosul- 

 phate of potash. But it is better to prepare the nitrosulphate 

 of ammonia. A concentrated solution is made of sulphite of 

 ammonia, which is mixed with 5 or 6 times its volume of so- 

 lution of ammonia, and into this, nitric oxide is passed for 

 several hours. A number of beautiful crystals are gradually 

 deposited ; they are to be washed with a solution of ammonia 

 previously cooled, which besides the advantage of retarding 

 their decomposition, offers that of dissolving less of them than 

 pure water. When the crystals are desiccated, they should be 

 introduced into a well closed bottle ; in this state they undergo 

 no alteration. The same process is applicable to the corres- 

 ponding salts of potash and soda. When a strong acid is added 

 to a solution of these salts, for the purpose of isolating the 

 nitrosulphuric acid, the latter on being set free, decomposes 

 spontaneously into sulphuric acid and nitrous oxide, which 

 comes off with effervescence. 



Properties. The acid of the nitrosulphates is not precipitated 

 bybarytes. The nitrosulphate of potash, when heated, becomes 

 sulphite, and evolves nitric oxide ; but the salts of soda and 

 ammonia become sulphates, and evolve nitrous oxide. No 

 nitrosulphates of the metallic oxides which are insoluble in 

 water, have been formed, or appear capable of existing; for 

 when such salts as chloride of mercury, the sulphate of zinc or 

 of copper, the persulphate of iron and the nitrate of silver are 

 added to the nitrosulphate of ammonia, they produce a brisk 

 effervescence of nitrous oxide, with the formation of sulphate 

 of ammonia, or they decompose the nitrosulphate of ammonia 

 as free acids do. Indeed the only nitrosulphates which have 

 been formed are those of potash, soda and ammonia. These are 

 neutral, and have a sharp and slightly bitter taste, with nothing 

 of that of the sulphites. 



These salts vie with the peroxide of hydrogen in facility of 

 decomposition. The nitrosulphate of ammonia resists 230, but 

 is decomposed with explosion a few degrees above that tempe- 

 rature, caused by the rapid disengagement of nitrous oxide. 



