204 PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND, 
' This last, generally in grains nearly the size of those of sand, is usually re- 
' garded as undecomposed mineral; this it cannot possibly be, if the powdered 
mineral has been dusted through fine linen, and so thoroughly mixed with the 
flux that reagglutination has not taken place; it may, however, be some new 
- compound formed during the fusion, especially if the latter has been over- 
'. heated. 
Although white and hard grains are to es regarded with suspicion, crushed, 
and treated longer with acid, yet they frequently prove to be little else than silica. 
I have separated and examined by refusion and boiling in solution of sodium 
carbonate this variety several times, generally finding mere traces of alumina 
and lime, never having got over 3°7 per cent. of alumina. 
The desiccation and granulation of the mixed silica and saline mass, gene- 
rally converts the flocculent silica into the granular ; and the hard gritty, which 
‘should always be crushed up, in the fear of its not being pure, also into the 
same. Should there, after granulation, be any new appearance of a hard, white, 
gritty powder, there has been overheating; and recombination between the 
silica, alumina, and lime; a white powder, so appearing, contains much larger 
quantities of bases than the before-mentioned white “ silica.” 
4. Is the Amount of Contamination incident upon the employment of Vessels 
of Glass of signal importance 2 
Weighings of three German glass beakers used in the one operatjon, namely, 
the dissolving up and granulating the acid solution, showed losses in weight of 
‘01, °078, and -189 grains. | 
‘If the solutions be allowed to remain alkaline for any length of time, the 
amount of material dissolved from the glass in common use is very material. 
_5°646 grains of silica were, after fusion with six times their weight of 
FRESCENIUS’ flux, dissolved in water, without being acidified, and dried twice in 
a glass beaker, sold as Bohemian ; on re-solution there was got 6° 361 grains of 
insoluble matter—a gain of 12°68 per cent. on the small quantity. In another 
similar operation, in which 4°88 grains of silica were used, the beaker lost - 246 
of a grain. Two others gave respectively a loss of ‘64 and °111 grains. 
Though such circumstances, or modes of operating in glass vessels, do not — 
occur in an analysis properly conducted, yet so material is the corrosion of glass 
_ vessels during many parts of the course, that I look upon an excess of from *2 ~ 
' to *7 per cent., when about 20 grains are employed, as indicating a more cor- — 
rectly executed analysis than anything more nearly approaching the 100. It 
being, therefore, recognised that during any overheating in the desiccation of 
the acid solution of the fluxed mineral, the silica re-enters into union with 
small quantities of certain of the bases; and it being also recognised that 
