204 
DR. GLADSTONE ON CIRCUMSTANCES MODIFYING 
The numbers in the preceding table are deduced from the experimental data, but 
they must be considered as only rough approximations to the truth. The notes of 
interrogation indicate that the means of determination were themselves open to doubt. 
Effect of differences of temperature. — The experiments narrated in this paper were 
all performed at the ordinary temperature. The slight changes that may have taken 
place in that respect from one day to another were incapable of affecting visibly the 
coloured solutions. Much greater variations had a perceptible effect, but whether 
this ever arose from changes in the balance of affinities I am not prepared to say. 
I now pass on to consider the testimony borne by other coloured salts, not ferric 
compounds, in respect to the question at issue. 
Gold salts. 
The bromide of gold is of an intense scarlet, whilst the chloride is of a yellow colour. 
Dr. G. Wilson has made use of this difference in examining the question as to whether 
haloid salts exist as such in solution*; which suggested to me the employment of the 
same salts for my own purpose. In respect to the relative merits of the two hypo- 
theses about haloid salts, it may be as well to state that I desire to express at present 
no opinion. If I write bromide of gold or sesquichloride of iron for the dissolved salts, 
I do so because that is the ordinary nomenclature. 
Pure chloride of gold free from hydrochloric acid was prepared. To a portion of 
this three equivalents of bromide of potassium were added. The formation of the 
scarlet terbromide of gold was so complete, that the addition of either of the salts 
employed caused, singly, too small an increase of colour to be readily appreciated. 
Is it to be considered, then, that the decomposition in this case has been complete? 
may it be represented thus — 
Au Cl 3 -f 3K Br= All Br3+3K Cl ? 
This was more rigidly tested by adding chloride of potassium in large excess to 
bromide of gold. This latter salt was prepared by dissolving gold leaf in bromine 
water, evaporating to dryness, and redissolving in water. 
Strong chloride Water added to 
of potassium comparative 
added. solution. 
Strong chloride Water added to 
of potassium comparative 
added. solution. 
5 measures=30 measures. 
10 measures =48 measures. 
20 measures=70 measures. 
35 measures=105 measures. 
50 measures=135 measures. 
75 measures=180 measures. 
Some difficulty was felt in determining the last numbers of this experiment, from 
the fact that the chloride of potassium had by its great excess converted nearly the 
whole of the bromide of gold into the yellow chloride, or still paler double chloride. 
* Vide Athenaeum, 1839, and the Edinburgh Academic Annual for 1840, p. 187. 
