222 
Dr . Thomson on some of 
3. Bichromate of Silver. 
In the year 1820 I received a letter from Mr. Dowler, 
who was at that time in the laboratory at Guy's Hospital, 
informing me that “ if a few drops of dilute nitric or sulphuric 
acid be added to a solution of chromate or bichromate of 
potash, so as to disengage the chromic acid ; or, indeed, if a 
little of either of these acids be added to a solution of chromic 
acid, and, subsequently, a dilute solution of nitrate of silver 
be added, a precipitate will form, consisting of very small 
transparent scales, composed, I believe, of chromic acid and 
silver.” He then mentions that he had not analyzed this 
salt, and that the same salt may be formed by adding dilute 
muriatic acid to the pulverulent chromate of silver, but not in 
sufficient quantity to decompose the whole, and applying heat. 
He mentions also some other cases in which these crystalline 
scales appeared during his experiments. 
I have hitherto abstained from noticing this salt, from a 
notion that Mr. Dowler might perhaps have some intention 
of laying the analysis and properties of it before the public. 
But as six years have elapsed without any farther observa- 
tions from Mr. Dowler, I think it right to state here the 
result of my trials to determine its nature. 
If we dissolve bichromate of potash in water, and acidulate 
the solution with nitric acid, nitrate of silver cautiously added 
will occasion no precipitate ; but on setting the liquid aside 
for 24 hours, if it be sufficiently concentrated, a number of 
small crystals are deposited : they are sometimes feather- 
shaped, sometimes oblique, four-sided prisms, terminated by 
rhomboidal faces, placed obliquely. They are opaque, have 
