CHEMISTRY. 359 



CHEMISTRY. 



ON THE PURIFICATION OF SULPHURIC ACID. 



Cameron found as much as one ounce of arsenious acid deposited from eight 

 pounds of oil of vitriol, and in his paper, published in the Chemical Gazette, 1856, 

 he expresses the opinion that such acid could not be rendered sufficiently pure for 

 accurate investigations. It is well known that the best method of freeing sul- 

 phuric acid from arsenic ia by passing a current of hydrochloric acid through the 

 oil of vitriol heated nearly to boiling. In order to test the practicability of thia 

 method in cases where large quantities of arsenic are present, an experiment was 

 made on quantities of sulphuric and arsenious acid in the above proportion, viz. 

 1 ounce to 8 pounds, A large portion of the arsenious acid remained undissolved, 

 and hence the experiment was performed under the most disadvantageous circum- 

 stances. After passing the gas through the heated acid for one hour, it still 

 exhibited traces of arsenic, but after continuing a strong current for half an hour 

 longer, the residual acid was so pure that no trace of arsenic could be detected by 

 Marsh's test. Hence we may conclude, as might have been presumed a priori, 

 that this process is available whatever may be the quantity of arsenic present. 



ON SOME COMPOUNDS OF PALLADIUM. 



Palladio-bichloride of potassium is usually prepared by gently heating proto- 

 chloride of palladium with aqua regia, and adding chloride of potassium ; or by 

 boiling the palladio-protochloride with aqua regia. A better method is to pass 

 chlorine through a concentrated hot solution of the palladio-protochloride. Almost 

 the whole of the- palladium is precipitated in the form of the bichloride compound, 

 and what remains in solution may advantageously be employed in preparing the 

 chloride of palladammonium. 



I am not aware of notice having been taken of the remarkable changes of 

 color of the palladio-bichloride of potassium, under the influence of heat. The 

 change is more striking than with red oxide of mercury, the salt becoming black 

 with a very slight increase of temperature, and resuming its scarlet color on 

 cooling. The conversion with the palladio-protochloride does not taka place 

 until the temperature has been very considerably raised and the salt fuses ; the 

 color then changes to brown. 



Cyanide of Palladammonium. — This salt was originally described as ammoni- 

 ated cyanide. It can be readily obtained by the addition of hydrocyanic acid to 

 an ammoniacal solution of chloride of palladammonium. It falls as a white 

 crystalline powder, which can be crystallised by resolution, &c. Analysis 

 showed it to be the salt described by Fehling. 



Sulphide of Palladammonium. — When dilute hydro-sulphuric acid, or very 

 dilute sulphide of ammonium, is added to a solution of chloride of palladammo- 

 nium, the precipitate formed is, in the first instant, of a bright red, or orange red 

 color, similar to the sulphide of antimony ; it changes very rapidly into brown or 

 brownish black sulphide of palladium. The red precipitate probably contains 

 palladammonium, but is not a permanent compound. 



Double Sulphocyanides of Palladimn, — Buchton has. described the double 

 sulphoeyanides of platinum, but I am not aware that the corresponding palladium 



