COMBINATIONS OF AURIN WITH MINERAL ACIDS. 21 



molecule of acetic acid. We therefore tried to obtain an 

 analogous benzoyl compound, and to determine in it, 

 after decomposition 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 decom- 

 posed by water; but only hydrochloric and acetic acids 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 formed (as we stated in our former paper) 

 by crystallizing aurin from hot aqueous hydrochloric acid 

 retain the latter obstinately, led us to the conclusion 

 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, crystallizing 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 



