1826.] On pure Caoutchouc. 179 



a tube, it became charred, yielding much ammonia. It re- 

 sembles albumen more than any other substance, and is the 

 source of the nitrogen or ammonia obtained by the distillation 

 of common caoutchouc. 



The brown aqueous solution (a) became frothy on agitation ; 

 alkali rendered it of a deep yellow colour, and produced a 

 putrescent odour, similar to that evolved by alkali or quick -lime 

 from white of egg or blood. It was remarkably distinguished 

 by the deep-green colour it produced with persalts of iron, 

 especially when a little alkali was present, and the dense yellow 

 precipitates it formed with muriate of zinc and nitrate of lead ; 

 indeed, precipitates were produced in solutions of most of the 

 metals by it. The colour produced with iron does not seem to 

 be a precipitate. 



With the hope of obtaining something peculiar from this 

 solution, a quantity of it was precipitated by nitrite of lead ; a 

 colourless solution and a yellowish-green precipitate were ob- 

 tained. The latter, being well washed, was next diffused 

 through water, and sulphuretted hydrogen passed through it ; 

 by filtration a deep brown solid was obtained and a yellowish 

 solution. The precipitate when washed and dried was brittle 

 and hard ; on platina-foil it at first burnt with flame, swelling 

 much, and giving out odour of ammonia like animal matter ; 

 after that sulphurous acid burnt off, and ultimately lead and 

 oxide of lead remained ; hence it was a combination of sul- 

 phuret of lead, and a highly azoted substance. Heated in a 

 tube, it gave out much ammonia ; digested in alcohol, scarcely 

 a trace of matter was removed. 



The sulphuretted hydrogen solution, being boiled and eva- 

 porated, left a yellow varnish-like substance, not deliquescent, 

 soluble in water, acid to taste and to litmus, the acid not being 

 sulphuric : it rendered persulphate of iron green, precipitated 

 nitrate of lead, and gave no ammonia by heat. 



The concentrated solution (a) acted upon by alcohol, had an 

 insoluble matter thrown down, which being separated and well 

 washed with alcohol, was afterwards treated with water, a deep 

 brown aqueous solution (b) was obtained, and a small insoluble 

 portion left ; this was almost black when dried, tasteless, brittle, 

 burning with difficulty, and when heated in a tube giving much 

 ammonia. 



