THE

ON THE

MANUFACTURE OF GLASS FOR VESSELS

EMPLOYED IN

CHEMICAL RESEARCHES.

By Professor J. S. STAS.

In my researches "on the Reciprocal Relations of Atomic Weights" I have stated that the ordinary glass of which retorts, flasks, &c., are made, gives up to nitric and hydrochloric acids at the ordinary temperature traces of the metals it contains. In such vessels it is impossible to evaporate the purest acid to dryness without leaving a saline residue. Hard Bohemian glass, known as refractory, and in general all glasses having no alumina, and containing an excess of silica, resist for an almost indefinite time the action of hot concentrated acids; but the manufacture of balloons, flasks, and retorts in refractory glass presents great difficulties, the most skilful workmen not being always able to work in it when articles are required of an extra large size. I have had this difficulty frequently brought before me.

Wishing to ascertain what should be the composition of glass which would be at the same time unaffected by acids and sufficiently fusible to be manipulated with no great difficulty, I decided to carry out some experiments on this manufacture in an actual glass house. These researches showed me that a glass having for bases sodium and calcium, if it contains a sufficient excess of silica, resists acids almost as well as refractory Bohemian glass, having for bases potassium and calcium. But it is known that a mixture of equal molecular weights of the carbonates of sodium and potassium is much more fusible than the most fusible of either carbonate by itself; starting from this fact, I have been led to the endeavour to replace, in the composition of refractory glass unattacked by acids, a portion of the potassium by an equivalent quantity of sodium. The result has completely verified my anticipations.

I started from this fact, that to obtain a glass very refractory and unattacked by acids, having for bases potassium and calcium, it should contain about

Silica

Oxide of potassium

Oxide of calcium

75'00

15:00

10'00

100'00

In this glass the bases are in the proportion of one atom of calcium (Ca" = 40) to one atom of potassium and one atom of sodium.

With these data I made some trials on a manufacturing scale; using for this purpose fine, pure sand employed in the manufacture of crystal glass, monocarbonate of potassium as pure as it comes from the English works, purified bicarbonate of sodium, and carbonate of calcium in the form of white marble, finely pulverised and passed through a silk sieve. These materials, in appropriate quantities, were intimately mixed with ten or twelve per cent of their weight of arsenious anhydride, and were then submitted in very refractory crucibles to a heat strong enough to bring them to a sufficient state of fusion to enable the glass to be worked. The addition of this enormous quantity of arsenious anhydride was made by the superintendent of the glass works, with the object of more readily determining the liquefaction of the mass. I confess I cannot understand the action of this; it produced, however, no other inconvenience than filling the air with torrents of poisonous matter, and analysis has satisfied me that no trace of the arsenic employed remains in the glass produced.

Operating with the proper proportions, two meltings were effected upon tolerably large quantities. With the glass obtained I had balloons with long necks, mat, rasses, small flasks, cylinders, &c., blown. The largest balloon which an excellent workman succeeded in making held about four litres; the capacity of the other balloons varied from one to three litres. The sides of the sphere were kept thick enough to be able to resist the traction to which the glass would be exposed by the shrinking experienced by nitrates when solidifying after fusion. This glass had a yellowish reflection; it was excessively hard, but little elastic, and as free from hygrometric properties the best refractory glass of Bohemia.

as

In these analyses I determined directly the silica, and the oxides of potassium and calcium. The oxide of sodium was estimated by difference. The glass also contained a little alumina derived from the crucible; I did not weigh it; the numbers for the sodium are therefore that much in excess.