440 Proceedings of the Royal Society 
containing a small asbestos filter, and the funnel was filled with 
strong commercial nitric acid. The acid was completely saturated, 
after passing two or three times through the wood. The solution 
had a dark-green colour by reflected, and a deep-purple red by 
transmitted, light. When poured into water, a copious but ex- 
tremely light flocculent precipitate, of a bright-green colour, was 
produced, which slowly subsided, leaving the supernatant liquid 
nearly colourless. As this precipitate was found to possess the 
same properties, whatever acid was used in its preparation, I had 
no hesitation in using nitric acid, which is by far the best solvent. 
On attempting to wash the precipitate with distilled water, either 
by decantation or on a filter, I found that, while nearly insoluble in 
moderately dilute acid, it dissolves to a considerable extent in 
water, even when the latter contains distinct traces of acid. I 
therefore had recourse to the method of dialysis to get rid of the 
acid. 
The acid liquid containing the green matter in suspension was 
placed on a dialysor, consisting of a sheet of parchment paper, 
stretched over a double ring of gutta-percha, and floating in a vessel 
containing distilled water. After two or three days (the water 
being frequently renewed) the nitric acid was found to be entirely 
removed, and the contents of the dialysor consisted of a green 
liquid, and a dark-green precipitate. The latter left a small white 
ash on ignition ; and as the quantity of ash bore no constant rela- 
tion to the quantity of green matter, it was obvious that the sub- 
stance was still impure. In order to purify it further, I took ad- 
vantage of its solubility in alkalies, and dissolved it in the smallest 
possible quantity of very dilute ammonia. The brown solution thus 
obtained was filtered, allowed to stand several days in the dialysor, 
and precipitated by means of hydrochloric acid. The acid was 
as removed by dialysis, and a green liquid and precipitate obtained 
before. This was dried in vacuo over sulphuric acid. 
The substance thus obtained is a very light powder, almost black 
when viewed in mass, dark bluish-green when finely divided, and 
is probably nearly pure. I have, however, not yet analysed it, as it 
still leaves a decided trace of ash ; and I am unwilling to expend 
the small quantity at my disposal until I have made further efforts 
to obtain it in a state of purity. 
