122 Dr. Brandes's Chemical Exammaiion 



metallic pellicle which was on the inside. This shows that the 

 cause of this tarnish was the same as that which acts upon 

 glass long exposed to the weather, — such as in old church win- 

 dows for instance ; and which has a similar appearance. How- 

 ever, to convince myself completely of the absence of gold, I 

 heated as many as possible of the shining glass leaves in nitric 

 acid, by which process the gold-coloured covering entirely dis- 

 appeared, and the leaves remained without colour. 



In order to find out the component parts of the glass, I sub- 

 mitted it to the following process : 



a) A portion of the glass was reduced to a powder and 

 boiled in nitric acid, the liquor filtered off and saturated with 

 ammonia, which threw down a precipitate that was again dis- 

 solved in nitric acid, and which gave no precipitate with sul- 

 phuretted hydrogen. Nor did sulphuric or muriatic acid pro- 

 duce any turbidity in it : but when that part of the solution 

 which had been treated with sulphuretted hydrogen was sa- 

 turated with ammonia, a blackish-green precipitate was pro- 

 duced, which, after being again boiled with nitric acid and 

 mixed with ammonia, gave a whitish precipitate, which became 

 browner by exposure to the air. This was again dissolved in 

 nitric acid, the product neutralized and mixed with benzoate 

 of potash, which gave a precipitate of a brownish-white : a 

 whitish cloud was produced in the liquid filtered from it, by 

 means of carbonate of potash. 



This precipitate, then, must have consisted of the oxides of 

 iron and manganese. After some re-actions, it seemed as if 

 some traces of arsenic were still left in the nitric solution : 

 however, the indications we^e too undecided to give this with 

 certainty. 



b) The ammoniacal liquor of(a) being evaporated to dryness, 

 the remaining substance was dissolved in dilute nitric acid. 

 In this solution, sulphuretted hydrogen gave a dark-brown 

 precipitate of sulphuret of lead. 



c) The precipitate not dissolved by nitric acid was ignited 

 with nitrate of barytes in a crucible of platinum, the remain- 

 ing mass dissolved in water acidulated with nitric acid, evapo- 

 rated to dryness, and the residuum extracted by acidulated 

 water. This consisted of pure silica. 



d) The acid solution (c) gave with ammonia a slight browai 

 flocculent precipitate, from which caustic potash extracted a 

 trace of alumina; and the rest was similar to the mixture of 

 iron and manganese in (a). 



e) The solutions treated with ammonia were freed from ba- 

 rytes by means of nitric acid, evaporated and ignited. The 

 small residuum that was left, was dissolved and crystallized 



