Dr. Turner on the Corn-position of Chloride of Barium. 183 



powder, boiled in successive portions of alcohol, and fused. 

 The fused chloride was redissolved in distilled water, and again 

 obtained in crystals. This salt dissolved without residue or 

 turbidity in water, and the solution was not affected by pure 

 ammonia ; it was not discoloured by sulphuretted hydrogen, 

 hydrosulphuret of ammonia, or chloride of lime; when preci- 

 pitated by an excess of sulphate of potash, the soluble parts 

 were not rendered turbid by an alkaline carbonate or oxalate 

 of potash ; and when thrown down by pure sulphuric acid, 

 evaporated, and ignited, the dry mass did not yield a trace of 

 any soluble sulphate to water. Both compounds were heated 

 to redness before being employed ; and the chloride of barium, 

 which if perfectly anhydrous, attracts moisture freely from the 

 atmosphere, was always placed while hot in a weighed bottle 

 secured by a tight cork, and its weight ascertained when cold. 

 This precaution is not necessary with sulphate of potash. 



I have thought it right to enter into these details, not only 

 that chemists may judge of the accuracy of my experiments by 

 the care with which they were conducted, but because the 

 error committed by Dr. Thomson appears referable to the 

 neglect of some of these precautions. This opinion seems the 

 more probable, since Dr. Thomson is uncertain whether in 

 his original experiments he did not employ the muriate of 

 baryta of commerce, and if so he doubtless must have operated 

 with an impure substance. But independently of any inac- 

 curacy arising from this source, I shall now endeavour to 

 prove that his method involves an error which precludes an 

 exact result even with the purest materials. When solutions 

 of muriate of baryta and sulphate of potash are mixed together, 

 a small portion of the latter invariably escapes decomposition, 

 and falls tenaciously adhering to the sulphate of baryta. I was 

 led to this fact by observing, that when a known quantity 

 of chloride of barium is precipitated by sulphate of potash, the 

 resulting sulphate of baryta always weighed more than when 

 the precipitation was made with pure sulphuric acid. The 

 appearance of the salts after exposure to a red heat, was like- 

 wise different; the impure sulphate being harder, more brittle, 

 and less opaque than the pure sulphate. The former reduced 

 to powder and boiled with water, yielded a solution which 

 precipitated barytic salts freely, and afforded certain evidence 

 of the presence of potash with muriate of platinum. 



The presence of sulphate of potash was at first naturally 

 ascribed to imperfect edulcoration ; but as it was still found, 

 even after the precipitate had been washed with unusual care, 

 I was led to examine the subject minutely. A solution of sul- 

 phate of potash was mixed with a large excess of muriate 



of 



