294 
DR. TURNER ON CHLORIDE OF BARIUM. 
rendered alkaline with pure baryta, in order to precipitate any oxide of iron 
or manganese which might be present ; and the crystals subsequently obtained 
by evaporation were reduced to 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 
precipitated 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 experi- 
ments 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 inaccuracy 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 decompo- 
sition, 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 likewise 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 so- 
