Sulphite of the Protoxide of Platinum and Soda. 275 



One of the most remarkable properties of this salt is, that 

 when dissolved in water, the presence of the platinum is not 

 indicated by the usual tests. The solution remains unchanged 

 upon the addition of hydrosulphuric acid and hydrosulphuret 

 of ammonia. Upon the addition of an acid however, the salt 

 seems to undergo decomposition, and the solution, even at the 

 common temperature, is slowly colored ; whereas by heating, it 

 immediately becomes brownish red, and at length the sulphuret 

 of platinum falls down. This precipitate is entirely soluble in 

 the hydrosulphurets of the alkalies. The salt does not however 

 seem to be decomposed by alkalies, as it is by acids. 



By acids, even when diluted, this salt is easily decomposed, 

 and, with the escape of sulphurous acid, dissolved. The solu- 

 tion in hydrochloric acid gives, when evaporated, crystals of 

 chloride of sodium; and upon the addition of ammonia, a green 

 somewhat crystalline precipitate, the platino-protochloride of the 

 hydrochlorate of ammonia. The solution in sulphuric acid gives, 

 by evaporating, crystals of the sulphate of soda, and exhibits then 

 the dark color of the sulphate of the protoxide of platinum. By 

 a certain concentration of the acid, metallic platinum falls down ; 

 a property which was found to belong to the sulphate of the 

 protoxide of platinum purposely prepared. The solution of the 

 salt in nitric acid assumes, upon evaporation, a brownish red 

 color; if sal-ammoniac is then added, no precipitate is formed; 

 if however the solution is evaporated almost to dryness, and 

 sal-ammoniac added, there is formed in abundance the platino- 

 bichloride of hydrochlorate of ammonia. The brownish red color 

 seems here to arise from the formation of the sulphate of the 



peroxide of platinum. 



In a solution of the cyanuret of potassium, this salt is very 

 soluble, and by evaporation, crystals of the platino-cyanuret of 



potassium are obtained. 



If this salt is exposed to the temperature of nearly 200°, (Centi- 

 grade,) it loses completely its water of composition. Heated to 

 240°, it undergoes no farther change, but when exposed to a 

 still greater heat it begins to suffer decomposition. This de- 

 composition is completely effected by long exposure to a red 

 heat, and a mixture of sulphate and sulphite of soda with me- 

 tallic platinum remains behind. 



In order to determine the quantity of the soda and the plati- 



num, 



ammoniac and then expose 



