30 
These salts, as we may call them, are "beautiful bodies, 
crystallizing exceedingly well, and although some of them 
are decomposed by water, they are very stable in dry air. 
To their discovery we were led by the following observa- 
tions. 
On heating aurin with glacial acetic acid and acetyl 
chloride, tire crystals lose at once their steel-blue lustre and 
assume a pale red colour. To obtain the compound thus 
formed in a pure state, acetyl chloride was added to a satu- 
rated solution of aurin in acetic acid. The liquid assumed 
at once a much lighter colour, and soon pale red needle- 
shaped crystals having a diamond lustre separated out. On 
recrystallizing these repeatedly from alcohol, we obtained 
oblong six-sided plates, which as analysis showed were pure 
aurin. 
On treating the original crystals with water, they become 
dull and brownish red, the solution containing acetic and 
hydrochloric acids. It therefore seemed not improbable that 
an additive product of aurin and acetyl chloride had been 
formed, containing however also acetic acid, as a superficial 
examination showed, that the liquid contained, to one mole- 
cule of hydrochloric acid, much more than one molecule of 
acetic acid. We therefore tried to obtain an analogous 
benzoyl -compound and to determine in it, after decompo- 
sition with water the relative quantities of hydrochloric 
and benzoic acids. 
On adding benzoyl chloride to a hot solution of aurin in 
acetic acid, similar crystals as before were obtained, which, 
after being dried on filter paper in dry air, were decompo- 
sed by water, but only hydrochloric and acetic acid went 
into solution, and on heating the product with water or 
alkalies but a mere trace of benzoic acid could be detected. 
These facts, coupled with the observation that the bright 
red needles which, as we stated in our former paper, are 
formed by crystallising aurin from hot aqueous hydrochlo- 
