31 
ric acid, retain the latter obstinately, led us to the con- 
clusion that this acid forms a definite compound with aurin. 
Such a body could be formed under the above conditions, 
as our glacial acetic acid contained a little water. More- 
over, Mr. Charles Lowe had informed us that the splendid 
specimen of aurin which he exhibited at Paris was obtained 
in the following way. The crude but crystalline aurin, 
which is obtained by heating pure phenol with sulphuric 
and oxalic acids, was dissolved in alcohol and some strong 
hydrochloric acid added, by which a crystalline precipitate 
was formed, crystallising from hot acetic acid in beautiful 
red, glistening, flat needles. He was kind enough to give 
us a sample, and on examining it we found that water 
acted upon it in the same way as on our crystals. 
In order to prepare a pure compound for analysis, a hot 
solution of aurin in acetic acid was saturated with hydro- 
chloric acid gas ; the colour of the liquid changed into a 
light yellowish red, and soon the compound separated out 
in glistening needles, which, even when perfectly dry, smell 
strongly of acetic acid. When exposed to the air, they soon 
assume a steel-blue lustre and gradually crumble into a 
reddish brown crystalline powder. The same properties 
are shown by the crystals obtained from acetyl chloride 
and those obtained from Mr. Lowe. When heated to 
110° in a current of dry air they gradually lose all the acetic 
acid, which plays the part of water of crystallisation, and 
assumes a dull red colour. 
On passing hydrochloric acid gas into an alcoholic solu- 
tion of aurin, similar but smaller needles are formed, con- 
taining alcohol, which is given off at 100° ; the dull red 
residue can, like the preceding one, be heated to 190° in a 
current of dry air without losing hydrochloric acid, which 
only begins to escape at 200°. 
Analysis of these compounds showed that the dried sub- 
stance consists of C 19 H u 0 3 , HC1, while the crystals obtained 
