of Bohemian Glass. 423 



II. 2*1284 grms ot" glass gave 0-0177 gi'm- of pyrophos- 

 phate of magnesia. 



f. Determination of the Alkalies. 



To determine the amount of the alkaUes, a portion of the 

 glass was fused with hydrate of baryta ; the fused mass was 

 digested in hydrochloric acid, evaporated to dryness and 

 ignited, the residue again digested in hydrochloric acid, and 

 then filtered from the insoluble silicic acid. Carbonate of 

 ammonia was then added to the filtrate, to separate the alumina, 

 sesquioxide of iron, baryta and lime ; the solution filtered 

 from the precipitate was evaporated to dryness and ignited, 

 to drive off the ammoniacal salts, and the magnesia separated 

 by means of baryta ; the excess of baryta was separated by 

 means of carbonate of ammonia, and filtered. The filtrate, 

 evaporated to dryness and ignited, yielded the mixed chlo- 

 rides of the alkaline metals ; they were dissolved in water, 

 bichloride of platinum added, and the solution evaporated to 

 dryness on a water-bath : the residue was digested in strong 

 alcohol, when the potassio-chloride of platinum remained un- 

 dissolved ; it was collected on a weighed filter, washed with 

 alcohol, and dried in a water-bath until it ceased to lose 

 weight. The filtrate from the potassio-chloride of platinum 

 was evaporated to diyness, and, after the addition of some 

 oxalic acid to the residue, ignited till it was completely de- 

 composed ; the residue was digested in water, filtered, and the 

 filtrate evaporated to dryness in a weighed capsule; its in- 

 crease in weight gave the quantity of chloride of sodium. 



1-5645 grm. of glass gave 0-9330 grm. of potassio-chloride 

 of platinum, and 0-0905 grm. of chloride of sodium. 



From the results enumerated, the calculated per-centage is 

 as follows : — 



I. II. Mean. 



Silica 72-84 73*42 73*13 



Lime 10*75 10*11 10*43 



Alumina 0*30 ... 0*30 



Peroxide of iron ... 0*13 ... 0-13 



Magnesia 0*21 0*30 0*26 



Protoxide of manganese 0*37 0*54 0*46 



Soda 3-07 ... 3*07 



Potash 11*4^ ... n*49 



99*16 99*27 



The amount of oxygen in the bases stands to the amount 

 of oxygen in the silicic acid nearly as 1 : 6. 



From the preceding analysis, it results that the composition 

 of the glass for combustion-tubes does not differ very much 



