270 Professor Gmelin's Analysis ofHelvine. 



at the same time, some lac sulphuris was precipitated, and, as it 

 seemed, sulphate of barytes, together with silica, not dissolved 

 by the acid. The solution was now evaporated to perfect 

 drvness in a water- bath, the residue treated with water and a 

 little muriatic acid, the substance left undissolved washed up- 

 on a nitre with boiling water and ignited, then boiled with 

 a solution of carbonate of potash, obtained by ignition of the 

 crystallized carbonate, and the solution filtered boiling. 

 There remained upon the filtre a white loose powder ; and 

 in the liquid, which had passed quite clear through the filtre, 

 a great quantity of a gelatinous semitransparent precipi- 

 tate of silica was formed, which was entirely dissolved again 

 by heating the liquor, and appeared anew by cooling.* The 

 powder that remained upon the filtre was carbonate of ba- 

 rytes, with traces of undecomposed sulphate of barytes. The 

 liquor separated from sulphate of barytes and silica by the 

 filtre was thrown down by carbonate of ammonia, filtered, 

 evaporated, and ignited. There was left a substance not so- 

 luble in water, which, because the absence of an alkaline sub- 

 stance had been proved, was not particularly examined.-f* 



(2.) The method of analysis followed in No. 1. not hav- 

 ing led to a satisfactory result, I inquired particularly whether 

 Helvine might not be decomposed by acids ; and then found, 

 that it is, in fact, decomposed by muriatic acid at a moderate 

 digestion heat, with the disengagement of sulphuretted hydro- 

 gen, and that it even forms a jelly with that acid. 



a. 1.927 grammes of the dried powder ofHelvine were poured 

 over in a porcelain dish with fuming nitric acid, free from sul- 

 phuric acid, and then a certain quantity of fuming muriatic 

 acid was added. By digestion a jelly was formed, the li- 

 quor heated to boiling, and evaporated at last at a moderate 

 heat to full dryness. Silica was separated perfectly white ; it 

 weighed after ignition 0.64088 gr. = 33.258 per cent. 



" Professor C. H. PfafF was the first, so far as I know, who observed, 

 that silica is perfectly and in abundance dissolved by the pure subcarbo- 

 nates of potash and soda, when heated with the solutions of these salts. 

 (Journ. of Schweigger, Vol. XXIX. p. 383.) 



t It appears from the following inquiry, that this substance was gly- 

 cine, which had been dissolved by the excess of carbonate of ammonia. 



